Car Park Designers' Handbook

Car park designers’ handbook

Jim Hill With contributions from

Glynn Rhodes, Steve Vollar and Chris Whapples

Published by Thomas Telford Publishing, Thomas Telford Ltd, 1 Heron Quay, London E14 4JD. URL: http://www.thomastelford.com Distributors for Thomas Telford books are USA: ASCE Press, 1801 Alexander Bell Drive, Reston, VA 20191-4400, USA Japan: Maruzen Co. Ltd, Book Department, 3–10 Nihonbashi 2-chome, Chuo-ku, Tokyo 103 Australia: DA Books and Journals, 648 Whitehorse Road, Mitcham 3132, Victoria First published 2005 Also available from Thomas Telford Books The Motorway Achievement volume 1. The British motorway system: visualisation, policy and administration. Edited by Sir Peter and Robert Baldwin. ISBN 07277 3196 3 The Motorway Achievement volume 2. Frontiers of knowledge and practice. Edited by Professor Ron Bridle and John Porter

A catalogue record for this book is available from the British Library ISBN: 0 7277 3438 5 # Thomas Telford Limited 2005 All rights, including translation, reserved. Except as permitted by the Copyright, Designs and Patents Act 1988, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior written permission of the Publishing Director, Thomas Telford Publishing, Thomas Telford Ltd, 1 Heron Quay, London E14 4JD. This book is published on the understanding that the authors are solely responsible for the statements made and opinions expressed in it and that its publication does not necessarily imply that such statements and/or opinions are or reflect the views or opinions of the publishers. While every effort has been made to ensure that the statements made and the opinions expressed in this publication provide a safe and accurate guide, no liability or responsibility can be accepted in this respect by the authors or publishers. Typeset by Academic þ Technical, Bristol Printed and bound in Great Britain by MPG Books, Bodmin, Cornwall

This book is dedicated to the memory of John Charles Cannon MA (Cantab), CEng, MICE, FIStructE

1931–2005 An outstanding engineer who, for 50 years, fought the effects of poliomyelitis with courage and determination.

Contents

Foreword Preface Glossary of terms Acknowledgements

1 Introduction 1.1 1.2 1.3 1.4

Historical note Advice and guidance Scope Design flexibility

2 Design brief 2.1 2.2

The client The brief

3 Design elements 3.1

3.2

3.3

3.4

3.5

3.6

The standard design vehicle (SDV): discussion 3.1.1 Length and width 3.1.2 Height 3.1.3 Wheelbase 3.1.4 Ground clearance 3.1.5 Turning dimensions 3.1.6 Recommended minimum diameters for turns up to 1808 between obstructions 3.1.7 Left side, right side or in the middle? Parking categories 3.2.1 Discussion 3.2.2 Car park categories Parking stalls 3.3.1 Discussion 3.3.2 Recommended dimensions for differing parking categories 3.3.3 Obstructions between stalls 3.3.4 Angled parking Aisle widths 3.4.1 Discussion 3.4.2 One-way-flow with reduced aisle widths 3.4.3 Two-way-flow-with reduced aisle widths 3.4.4 Manoeuvring on aisles 3.4.5 Turning between aisles Bin dimensions 3.5.1 Discussion 3.5.2 Recommended minimum bin dimensions for parking with 2.400 m-wide stalls Ramps and access-ways 3.6.1 Discussion 3.6.2 Recommended maximum vehicle gradients 3.6.3 Transitional slopes 3.6.4 Ramp projections into aisles 3.6.5 Storey height ramps

xi xiii xiv xvi

1 1 2 2 2

4 4 4

6 6 6 6 7 7 8 8 8 8 8 9 9 9 9 9 10 10 10 11 12 13 13 13 13 13 13 13 16 17 17 17

3.6.6 3.6.7 3.6.8 3.6.9 3.6.10 3.6.11 3.6.12 3.6.13

Side clearance Manoeuvring envelope Stall access One-way-flow ramp widths: discussion Ramp widths and angled parking Two-way-flow ramps Turning circle templates Two-way-flow: recommended minimum clear ramp widths 3.6.14 Scissors-type ramps 3.6.15 Side-by-side ramps 3.6.16 Circular ramps 3.6.17 Recommended minimum diameters for full circle ramps between limiting wall faces 3.6.18 Recommended minimum widths for circular ramp lanes between wall faces 3.7 Interlocking ramps 3.7.1 Stadium type 3.7.2 Circular type 3.8 Kerbs 3.9 Super-elevation 3.10 Parking deck gradients 3.11 Headroom and storey heights 3.12 Height limitations

4 Dynamic considerations 4.1

Discussion 4.1.1 Impact speeds 4.1.2 Effects of rain 4.1.3 Exit and entry rates and internal movement 4.1.4 Dynamic capacities for different stall widths and categories 4.1.5 Stopping distance 4.1.6 Speed limits 4.1.7 Dynamic capacities of ramps and access-ways 4.1.8 Dynamic capacities of cross-ramps and access-ways, per hour 4.1.9 Dynamic capacities of parking decks; calculations 4.1.10 Dynamic efficiency

5 Static considerations 5.1

Static 5.1.1 5.1.2 5.1.3

efficiency, discussion Relative efficiencies Area per car space Recommended capacities

6 Circulation design 6.1 6.2 6.3 6.4

6.5

Discussion How many levels? Roof considerations Circulation efficiency 6.4.1 Discussion 6.4.2 Shortest travel distance 6.4.3 Examples of circulation efficiency Parking times 6.5.1 Discussion

17 18 20 20 21 21 22 22 22 22 22 24 24 24 24 24 24 25 25 25 25

26 26 26 26 26 27 27 27 27 28 28 29

30 30 30 31 31

33 33 33 33 34 34 34 35 35 35

7 Circulation layouts 7.1 7.2 7.3

7.4 7.5

7.6

7.7

7.8

Discussion Dimensions used User-friendly features 7.3.1 Discussion 7.3.2 Simplicity 7.3.3 Crossovers 7.3.4 Circulation direction 7.3.5 Dead ends (culs-de-sac) Angled and right-angled parking: a comparison Split-level decks (SLDs) SLD 1 One-way traffic flow with an included rapid outflow route SLD 2 One-way traffic flow with an excluded rapid outflow route SLD 3 One-way-flow with side-by-side ramps (scissors type) SLD 4 Combined one-way-flows, three bins or more wide SLD 5 Combined one- and two-way-flows, three bins or more wide SLD 6 Two-way-flow with ‘combined’ ramps SLD 7 One-way-flow with an included contra-flow rapid exit route Sloping parking decks (SDs) SD 1 Single helix with two-way-flow SD 2 Single helix with one-way-flow and a rapid outflow route SD 3 Double helix, end connected with one-way-flow on the central access-way SD 4 Double helix, end connected with two-way-flow on the central access-way SD 5 Interlocking double helix, with one-way-flows SD 6 Combined helix, side connected with one- and two-way-flows SD 7 and 8 Double helix, side connected, with one-way-flows Combined flat and sloping deck (FSD) layouts FSD 1 Single helix with two-way-flow FSD 2 Single helix with one-way-flow and a rapid outflow route FSD 3 Combined helix, side connected with one- and two-way-flows FSD 4 Combined helix, side connected with one-way-flow FSD 5 Double helix, side connected with one-way-flow FSD 6 and 7 Double helix, side connected with one-way traffic flows FSD 8 Single helix with one-way-flow and an internal ramp Combined flat and sloping deck layouts with internal cross-ramps (VCM and WPD) VCM 1 One-way-flow with two one-way-flow ramps VCM 2 One-way-flow with end ramps VCM 3 Two-way-flow with a single end ramp VCM 4 One- and two-way traffic flows with a single ramp

37 37 37 37 37 37 38 38 38 38 43 44 46 48 50 52 54 56 59 60 62 64 66 68 70 72 75 76 78 80 82 84 86 88 91 92 94 96 98

7.9

7.10

7.11 7.12

7.13

WPD 1 Warped parking decks with one-way-flow Flat decks with storey height internal ramps (flat with internal ramps – FIR) FIR 1 One-way-flow decks with combined two-way-flow ramps at right-angles to the aisles FIR 2 One-way-flow decks with side-by-side (scissors type) ramps at right-angles to the aisles FIR 3 One-way-flow decks with combined two-way-flow ramps parallel with the aisles FIR 4 One-way-flow decks with separated one-way-flow ramps Minimum dimension (MD) layouts MD 1 One-way-flow between circular end ramps MD 2 Two-way-flow with a circular ramp at one end MD 3, 4 and 5 One- and two-way-flows, ten stalls wide MD 6, 7 and 8 One- and two-way-flows eight stalls wide (VCM type) MD 9, 10 and 11 One- and two-way-flows eight stalls wide (split-level type) Circular sloping decks (CSDs) CSD 1 Circular parking deck with two-way-flow Half external ramps (HERs) HER 1 Half spiral with one-way-flow HER 2 and 3 Straight ramps with one-way-flow HER 4 Straight ramps with one-way-flow, end located HER 5 Straight ramps with one-way-flow, end located External ramps (ERs) ER 1 Full circular with a two-way traffic flow ER 2 Full circular ramps each with a one-way traffic flow ER 3 Straight ramps with a one-way traffic flow ER 4 Storey height, straight ramps ER 5 Stadium-shaped interlocking ramps ER 6 Circular interlocking ramps

8 Stairs and lifts 8.1 8.2

8.3 8.4

Discussion Vertical and horizontal escape 8.2.1 Stairs, widths of flights 8.2.2 Vertical escape 8.2.3 Horizontal escape Escape distances Lift sizing

9 Disabled drivers and carers 9.1 9.2 9.3 9.4

Discussion Stall locations Stall dimensions Access

100 103

104 106 108 110 113 114 116 118 120 122 125 126 129 130 132 134 136 139 140 142 144 146 148 150

153 153 153 153 155 155 155 156

161 161 161 162 163

10 Cycles and motorcycles

165

10.1 Discussion 10.2 Cycle parking

165 165

10.3 Motorcycle parking 10.4 Lockers 10.5 Fiscal control

165 166 167

11 Security

169

11.1 11.2 11.3 11.4

169 169 170 170

Discussion Lighting, music and CCTV See and be seen Women-only car parks

12 Underground parking 12.1 Discussion

13 Lighting 13.1 Discussion 13.2 Emergency lighting

173 173

175 175 175

14 Signage

177

14.1 14.2 14.3 14.4 14.5

177 177 178 178 179

Discussion Directional signs Information signs Variable message sign systems Emergency signs

15 Drainage 15.1 Discussion

16 Fire escapes, safety and fire fighting

181 181

183

Discussion Escape distances Fire safety Fire-fighting measures Sprinklers Fire escapes

183 183 183 183 184 184

17 Fiscal and barrier control

187

17.1 Discussion 17.2 Control systems 17.3 Barrier control

187 187 188

16.1 16.2 16.3 16.4 16.5 16.6

18 Ventilation 18.1 18.2 18.3 18.4

Discussion Natural ventilation requirements Mechanically assisted natural ventilation requirements Mechanical ventilation requirements

19 Structure 19.1 19.2 19.3 19.4 19.5 19.6 19.7 19.8

Discussion Construction materials Joints Perimeter protection Concrete finishes Protective coatings Waterproofing Cambers

20 Appearance

191 191 191 191 191

195 195 195 196 196 197 197 197 198

201

20.1 Discussion 20.2 Appearance requirements

201 201

Appendix A

203

References

204

Index

205

About the authors

James Hill CEng FIStructE (ret’d)

Glynn Rhodes BSc (Hons) CEng MICE MIHT FConsE

In 1967 Jim founded the Hill Cannon Partnership (HCP) with John Cannon and has been involved in car park design since 1969. In 1970, they developed the Tricon structural system and in 1993 Jim patented the Vertical Circulation Module system (VCM). He is a past President of the British Parking Association and a regional Chairman of the Concrete Society. He is now a consultant to the practice, having retired in 1992, since when he has concentrated on the further development of VCM, designing appropriate circulation layouts for many projects and researching this book. He is currently writing a similar handbook on ‘good practice’ parking in the USA. Glynn is a senior partner of the HCP and has been involved in the design of 30 multi-storey car parks since 1986, two of which have been voted Best New Build car parks at the annual British Parking Awards. He also received the Ernest Davies Award for the best article published in Parking News entitled ‘Current Trends in the Design of Car Parks’. He has provided design advice for large underground car parking facilities in Manila, Kuala Lumpur (Petronas Towers), Zagreb and Dubai. Recent projects include the Jubilee car park in Harrogate (precast with 450 spaces), Merryhill Shopping Centre, West Midlands (precast with 1600 spaces) and Manchester Royal Infirmary (precast with 1600 spaces). Steve is a senior partner of the HCP and has been actively involved with car park design and parking related subjects since 1996: these include structured car parks, both above and below ground, as well as large capacity single deck layouts. His particular interest is in the provision of suitably located parking for disabled drivers, two wheeled traffic and general ‘wayfinding’ for both motorists and pedestrians alike. Recent design projects include Birmingham Airport (precast with 1700 spaces), Ocean Terminal; Edinburgh (precast with 1000 spaces) and Clarence Dock; Leeds (precast with 1600 spaces).

Stephen Vollar Eur Ing BSc CEng FIStructE MICE FConsE

Christopher Whapples BSc (Hons) CEng FIStructE FICE MIHT FConsE

A senior partner of the HCP, Chris has been involved in the design of parking structures for more than twenty years. He is a contributor to the IStructE publication Design recommendations for multi-storey and underground car parks and the Institution of Civil Engineers’ publication Recommendations for inspection, maintenance and management of car park structures. He has served on European technical committees and has presented papers on parking related subjects. His particular interest is in the development of new structural forms. Recent design projects include St. Andrews; Norwich (steel frame with 1100 spaces), Sundials; Amersham (steel frame with 550 spaces) and Designer Outlet Village, Livingston (in situ with 1600 spaces).

Foreword

Jim Hill has spent the last 35 years in the development of car park design and this experience has given him a unique insight into the reasons why some buildings operate successfully and others, of a similar size and activity, do not. The choice of the correct circulation layout is a subject that he considers to be of prime importance in the creation of an efficient parking building. Both as a consumer of parking services and a former parking manager, it always intrigues me why some parking layouts are easily navigated and yet others test one’s patience? As an engineer, I think logically and admire the ‘art of parking’ created by my fellow colleagues; as a consumer I want to be able to park my car as quickly and as effectively as I can and get on with the business in hand, be it work or play; this is especially true if I have children with me. My experience has taught me that parking is a means to an end; it is the first and last impression of my ‘destination’; it needs to be good if I’m to contemplate returning there again and again. This is especially true in the retail and commercial world where (hopefully) my custom is valued. It is equally true when I visit an unfamiliar town or city, park at a rail station, or simply spend a day at leisure someplace. Equally important is the need to feel intuitively safe and welcome wherever I choose to park. Complex layouts, frustration with queues and conflict with others who are manoeuvring about in or out of parking spaces, or sometimes in what seems like a never-ending set of twists and turns to get in or out of the car park in the first place, only serve to increase my sense of ‘uncared for’ by the owner or operator. This book, describes and illustrates some 60þ variations on the many ‘layout themes’, no doubt there are others. Their advantages and disadvantages are discussed, recommendations made for their practical application and suggestions made for other layouts that should also be considered. More than just discussing layouts, the author has shown how ramps can be prevented from projecting excessively into traffic aisles, how to assess dynamic capacity and efficiency, and the many other considerations that go to make up the design process. The matters dealt with in Chapters 8 to 20 such as the current requirements for people with mobility impairments, pedestrian access, security, ventilation, etc. have been written with the help of his partners, all parking experts in their own right. In the author’s opinion, effective design is based upon common sense, a little crystal ball gazing and experience: it is not a precise art. He suggests that, provided drivers will want to frequent the car park and clients are willing to pay for it, little else matters. I wouldn’t want to disagree with him, but my comments about being ‘welcome’ at any parking facility are the key to its success. If the operator wants to do business, good customer service is vital; to do that needs good design. This book addresses the subject of car park design, especially the design of circulation layouts, in a practical manner and can be easily

understood by anyone with an interest in the subject. It will help to identify examples of best practice in making our parking facilities more accessible to all. The book is also a useful reference for those considering the Park Mark1 Safer Parking Scheme. Kelvin Reynolds Kelvin is Director of Technical Services at the British Parking Association and Head of the Safer Parking Scheme.

Preface

Information on the design of vehicle circulation systems in car parks is hard to find: had it not been so this book, probably, would not have been written. To my knowledge, special features and relative efficiencies of car parks have never before been discussed in any great detail. Many designers are unaware of the advantages of using a particular layout system over another and it is a major purpose of this book to redress that imbalance. In 1968, John Cannon and I first became involved in car park structures when we were retained to design the foundations and nonstandard elements for a proprietary precast concrete system. A local car park incorporating this system had become the subject of adverse comment by many who used it, convincing us that we could do better ourselves. Our first effort was to develop a clear-span structure that was efficient, economical, aesthetically pleasing and capable of being constructed using structural steel as well as precast and cast in situ concrete: this was a successful venture and after more than 35 years it is still being used in many car park designs. In time, however, it became clear that no matter how efficient the structural solution was and how attractive the architectural appearance, if it was wrapped around a poor choice of circulation layout the result was yet another unpopular car park. In many under-used car parks, the reason for their unpopularity is not that that they have been allowed to become dirty and/or dingy (conditions that by themselves would not normally put off most motorists), but rather that they suffered from a poor choice of internal layout. Of the many buildings inspected, the most unpopular have, invariably, incorporated inappropriate circulation designs. Rather than giving these car parks an expensive cosmetic ‘makeover’, the money would have been better spent on improving the layout, even at the cost of losing, possibly, a few parking stalls. Over the years, as we became more experienced, so our awareness of the number of different layouts available increased. Fifteen years ago I decided to list them and recommend when and where they could be put to best use. This endeavour was interrupted in 1992 by the development and promotion of the vertical circulation module (VCM) circulation system. It was just as well, as the number of different layouts has risen even further since then. Some have been rejected as being impractical or just plain whimsical, but those that are featured in this book are practical and have been constructed somewhere but not always in the UK. With more than 6000 car parks in the UK, 30 000 in the USA and many thousands more in the rest of the world, it is unlikely that all of the possible variations will have been covered, and if any reader is aware of a practical circulation layout substantially different from those featured and lets me know, if it is included in a future edition they will be acknowledged as the source. Finally, I would like to thank my wife Rosalie who not only accompanied me on my travels around the car parks of several countries without complaint, but was also of invaluable assistance in suggesting improvements to the text and correcting my grammatical errors: any that remain are entirely my own fault.

Glossary of terms

Access-way or crossway A traffic lane without adjoining stalls laid flat or to a slope not exceeding 5%, also capable of being used by pedestrians. Aisle A traffic lane with adjoining stalls on one or more sides. Bin Used to denote the dimension across an aisle and its adjacent stalls. (A half bin has stalls only on one side.) Circulation efficiency A method of comparing the travel distance required to search the stalls, in any particular car park, with the minimum travel distance. (Given as a percentage.) Congestion Applies to traffic that is unable to flow freely. Cross-ramp An inclined traffic lane connecting the aisles in adjacent bins, laid to a slope greater than 5%. Deck A single floor that extends over the plan area of a parking building. Des Recs A shortened form of words describing the Design Recommendations for Multi-storey and Underground Car Parks, 3rd edition, published in June 2002 by the Institution of Structural Engineers. Dynamic capacity A measure of the rate that traffic can pass a given location within a car park. (Given in vehicles per hour.) Dynamic efficiency A measure of the ability of a car park to process vehicles under normal operating conditions. Excluded Applies to an inflow route that is separated from an outflow route. Extended Applies to any traffic route that is not rapid. Included A flow route that is located within the circulation pattern of another. Inflow Applies to the search path for traffic within a car park.

Manoeuvring envelope (ME) The boundaries established by the minimum turning circle when entering a crossway or ramp, outside of which a vehicle is unable to manoeuvre without reversing. MPV The initials for a multi-purpose vehicle. MSCP The initials for a multi-storey car park. One-way-flow Traffic flowing in a single direction on an aisle. Outflow Applies to traffic exiting from a car park. Ramp Any traffic lane, without adjoining stalls, that provides access to or from parking at different levels. Rapid Applies to a short route for inflow or outflow traffic. Stall The parking area allotted to a single vehicle, exclusive of any other adjoining area. Stall pitch The spacing for stalls, normal to an aisle, for a particular angle of parking. Static capacity The total number of stalls contained within a designated area or complete car park. Static efficiency The area of the parking decks divided by the static capacity and given as an area per stall. SUV The initials for a sports utility vehicle. Swept path The width on plan established by a vehicle for any given radius of turn. Two-way-flow Traffic flowing in both directions on an aisle, ramp or crossway. Vph Vehicles per hour.

Acknowledgements

Figs 1.1, 3.1, 3.2, 3.3, 3.5(a) and (b), 3.7, 3.8, 3.9, 3.10, 3.11, 3.17, 3.19, 3.20, 6.1, 7.2, 7.3, 7.5, 7.7, 7.8, 7.9, 8.1, 9.1, 10.1(a), 11.1, 12.1, 13.1, 14.1, 15.1, 16.1, 17.1, 19.1 and 20.1 Hill-Cannon archives. Figs 7.4 and 7.6 courtesy of Dundec Ltd. Fig. 7.10 courtesy of Norwest Holst. Fig. 10.2(c) courtesy of Falco. Fig. 10.3(d) courtesy of Motoloc Ltd. Fig. 18.17 courtesy of PSB (UK) Ltd.

1

Introduction

Rules and regulations are but the paper bastions behind which the inexperienced fight their battles, but in the matter of car park design let common sense prevail.

1.1 Historical note

Eugene Freyssinet, 1879–1962, a French structural engineer and the inventor of prestressed concrete, is credited with designing the first European multi-storey car park (MSCP) in 1920: a split-level layout. In the British Isles, the first multi-storey car park was built c.1924 and it is conservatively estimated that there are now well over 6000 in existence, many of which were constructed in the post-war boom years between 1950 and 1975. In the early years little information was available concerning the design of this new type of building and was mainly to be found in technical literature distributed by specialist construction firms. The manoeuvring geometry of vehicles, however, imposed a strong practical discipline resulting in the general principles of layout and design rapidly becoming rationalised, with split-level decks and one-way traffic flows used in many of the earliest buildings designed specifically for parking cars. Independent information gradually became more available, especially after the publication in 1969 of the AJ Metric Handbook and in 1970 of the BPA Technical Note # 1. Metric Dimensions for Car Parks – 908 Parking and in 1973, at a Joint Conference on Multi-storey and Underground Car Parks organised by the Institution of Structural Engineers and the Institution of Highway Engineers, a paper, by B. R. Osbourne and W. P. Winston, was presented that contained most of the relevant information available at that time relating to parking geometry. Design Recommendations for Multi-storey and Underground Car Parks was published in 1976: the first time that an attempt had been made to create a national standard work on car park design. It contained much of the information presented at the Joint Conference, together with relevant parts of Report LR 221 by the Road Research Laboratory published in 1969 and titled, Parking: Dynamic Capacities of Car Parks. The report was omitted from subsequent editions. Historically, MSCPs in the UK have suffered an unenviable reputation for poor layout design and quality of parking. The problem has always been in balancing the motorist’s desire for ample room in which to park with the client’s desire to build as economically as possible but, in a highly competitive market, designers sometimes went too far in the direction of pure economy and cost conscious clients were insufficiently critical about poor design features. This resulted in car parks that were lacking in essential dimensions; many were poorly constructed, inadequately waterproofed, badly lit, awkward to park in and insecure but, mostly, they had the merit of being cheap to build. Modern social trends recognise that parking quality plays a major role in the choice of destination for motorists and their families. Car parks provide, quite often, the first and last impression that they experience when visiting an urban location or commercial enterprise and have a significant influence on any decision they may make to return. Over

1

Fig. 1.1 1910 Ford in a 1990 car park

the years, there has been little change in the manoeuvring envelope of cars licensed to drive on the public highway and Fig. 1.1 shows that, even in 1910, car manoeuvring envelopes were not dissimilar to that of today’s vehicles and a well designed modern car park can be used by vehicles of all ages.

1.2 Advice and guidance

Multi-storey car parks are, basically, utilitarian constructions. Their design is not a finite art; it is a compromise, a balancing act between motorists’ spatial desires and the practical need to achieve economy of construction and effective use of the site area. Stall dimensions, aisle, ramp and access-way widths, ramp slopes, headroom and circulation layouts can all vary, the only real criterion being that of general acceptance by the motorist. The purpose of this handbook is to provide advice and guidance on those aspects that will enable car parks to perform their function efficiently, economically and at the same time, be ‘user friendly’.

1.3 Scope

The contents cover the practical aspects of design for self-parking facilities. Block parking and valet parking, where attendants park cars, have been excluded. Also excluded are mechanically operated car parks and matters concerning architecture, except where they are affected by practical considerations.

1.4 Design flexibility

A multi-storey car park, whether above or below the ground, is costly to construct and consideration should be given to possible changes of parking function during its working life. Initially, it might seem sensible and economical to provide minimum dimensions and standards to suit a particular purpose. Within time, however, its parking category may change and, unless the interior layout is sufficiently flexible to cope with these changes, the facility could become redundant. Example 1: a multi-storey car park serving a town centre bus station that was then relocated. The site was sold for retail development and the car park was offered as part of the deal. The layout, although adequate for its original purpose, was not suitable for shoppers, so a 500-space building in good order had to be demolished. Example 2: a large factory that closed down and was sold for retail development. The car park for the workforce, designed to minimum standards, was unsuitable for use by the general public. It, too, had to be demolished. Thirty years ago it was rarely considered that car parks could be bought and sold, and that the role for which they were originally

2

Car park designers’ handbook

designed would alter. Nowadays, however, they are being bought and sold in increasing numbers, either individually or collectively. Market values depend not so much on their architectural merits but on their popularity with the parking public, and as such they should be designed, within reason, to be as flexible as possible.

Introduction

3

2 Design brief

2.1 The client

Not all clients have an expert knowledge about car parks. They are conscious of the need to provide a certain number of parking spaces at a given location, but they are not, necessarily, aware of the information that is required in order to produce the most efficient and cost effective building. Designers should present their clients with a questionnaire in order to obtain the maximum amount of relevant information as early as possible. It is unlikely that it will all be available at the preliminary stage, but it does no harm to ask the questions and, at least, it establishes the designer’s expertise in the subject.

2.2 The brief

Apart from items such as ground investigation reports and accurate site and level surveys, both of which may require an unacceptable financial outlay by the client at an early stage, briefs should include as much of the following information as possible: . .

. .

.

.

.

.

.

. .

.

.

. .

.

4

The maximum and minimum number of spaces required. A plan of the proposed site to a known scale, showing the building lines and the surrounding access roads. Site levels, even if they are only approximate. Proposals for future development that might have an effect upon the setting out, shape and function of the building. The presence and, if possible, the location of electric cables, gas pipes, drains and sewers that might occur under the site, especially those that must not be moved or built over without special precautions being taken. The maximum number of parking levels and height of building required by the client or allowed by the local planning authority. The proposed use, whether it is to be a long-, medium- or short-stay facility, together with the anticipated vehicle entry and exit traffic flow figures. The category of parking required, bearing in mind the possibility that it could be sold at some future date for another purpose category. The proposed method of payment to be adopted for financial control, whether it is to be a ‘payment on exit’, ‘payment on foot’, a ‘pay and display’ system, or even no payment at all. The client’s preference, if any, for a particular type of construction. The accommodation required for staff and the general public, (offices, rest rooms, toilets, etc.). The capacity and preferred location for lifts and/or escalators. This is an especially important item when in conjunction with retail shopping. The requirements for water-protection over the top parking deck, either with asphalt or an elastomeric membrane, or leaving the top deck untreated, or even roofing over the complete building. The need to provide heating to exposed ramps. Whether a mechanical means of ventilation is acceptable: an important issue when the building is close to adjacent site boundaries. The client’s preference, if any, for standards of finish in lift lobbies, escape stairs, parking floors and exposed parts of the internal structure.

.

.

.

.

Design brief

The levels of interior lighting to be adopted (if it varies from British Standards), and any other instructions regarding painting of the interior that could affect the lighting design. The requirements for security, closed-circuit television (CCTV), patrols on foot, or any special emphasis on ‘user friendly’ aspects. The standards required for external and internal signs (illuminated and painted). The provision of water and power supplies for cleaning purposes.

5

3 Design elements

3.1 The standard design vehicle (SDV): discussion

More than 50 different car manufacturers offer some 340 models for sale to the general public in the UK. Add to that the makes and models that have been discontinued over, say, the past 15 years but can still be seen in reasonable quantities and the number rises to well over 500. In size they range from the diminutive Smart car up to the American ‘stretched limousines’ (see Fig. 3.1), some of which have found their way to the UK. To build a car park that can cater for them all is unrealistic and uneconomic. Large, limousine-type vehicles occur in relatively small numbers and very few are ever likely to require parking within a structured public car park. It has, therefore, become established practice to design car parks to readily accept the smallest 95% of privately licensed vehicles registered to drive on the highway (see Appendix A). That does not mean to imply that some of the larger vehicles must not enter a parking building, but that they must do so with greater care than the 95-percentile vehicle. The introduction of the multi-purpose vehicle (MPV) and the proliferation of four-wheel drive (4WD) vehicles in private ownership has resulted in an increasing use of bulkier and taller vehicles by the motoring public. It is likely that the trend will be towards even greater numbers of this type being parked as leisure activities expand and become an increasingly important factor in the choice of personal transportation. Although not frequent visitors, it would be an advantage for larger-type vehicles to be able to circulate (see Figs 3.2 and 3.3), even if they have to overflow into adjacent stalls in order to park. The most testing time can sometimes occur when the building is officially opened and the mayors or chief executive officers (CEOs) in their official limousines are taken on a ceremonial drive through the car park. It has happened!

3.1.1 Length and width A rectangle 4.800 m by 2.000 m on plan will accommodate 95% of the privately owned vehicles in the UK. The width is measured overall including the wing mirrors. Without wing mirrors the width can be assumed as 1.800 m (see Fig. 3.4). 3.1.2 Height In height, most cars are less than 1.500 m, but there is a growing number of 4WD and sports utility vehicle (SUV) type vehicles using car parks that should not be ignored. Of these, among the tallest currently in use, without roof racks, are the Land-Rover Defender (2.035 m) and the Discovery (1.919 m). Although not sold in large numbers, they can be frequent visitors, especially to provincial and market-town car parks. Vehicles made for volume sales will, most probably, always be capable of being driven into a standard domestic garage and it is unlikely that they will ever exceed a height of 1.950 m. Camper-type vans, also, do not always fall within the standard design vehicle (SDV) envelope, but in some ‘resort’ car parks there may be a need to accommodate them, even if only at the ground parking level.

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Fig. 3.1 Even in the USA, stretched limos have to park outside

Fig. 3.2 This Cadillac was able to drive through a building designed to ‘recommended’ circulation standards, even though it was necessary to climb to an emptier upper level in order to park

Fig. 3.3 In some car parks Rolls-Royce- and Bentleysized cars are not uncommon visitors

3.1.3 Wheelbase A wheelbase of 2.900 m is used to provide the worst-case scenario for changes of level at steep ramps and inclines (see Fig. 3.2). 3.1.4 Ground clearance Although the normal ground clearance for the SDV is better than 150 mm, a well-laden vehicle could be less, especially at the rear end.

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A dimension of 100 mm, therefore, is considered to be a reasonable minimum for design purposes (see Fig. 3.4). 3.1.5 Turning dimensions Vehicles operating within the SDV envelope are capable of turning between wall faces 12 m apart (see Fig. 3.4). Many large vehicles can also turn within this diameter but a very few need as much as 15.000 m to complete a 1808, wall-to-wall turn on full lock. At a speed of 10 mph, it takes approximately 4.500 m (one second’s driving) to develop a 908 turn with a radius of 9.000 m and this has to be taken into account when considering the turning manoeuvre. It is unreasonable to expect motorists to drive around a car park to the extreme manoeuvring ability of their vehicle. Long before this condition is reached, they will have abandoned the building for less onerous places to park, but occasionally it will be necessary to use a full-lock turn when entering a stall, or to avoid a pedestrian or another vehicle. This is acceptable but, for good parking practice, motorists must be given the ability to manoeuvre readily in either direction. As a general rule, the minimum turning circle for manoeuvring between adjacent aisles should be in the order of 150% of the SDV turning circle where 908 turns into and out of cross aisles and ramps are the norm and 200% where 3608 turns are anticipated. 3.1.6 Recommended minimum diameters for turns up to 180o between obstructions For good practice 18.000 m Tight – mainly for ‘long stay’ with light usage 16.000 m Very tight – for private use only, on small awkward sites and with the client’s prior agreement 14.000 m Entering and leaving parking stalls 12.000 m 3.1.7 Left side, right side or in the middle? Vehicles of different dimensions occupy stalls: quite frequently a small car is sandwiched between two larger vehicles and it can appear that the stall is empty until the viewing angle improves. This is an especially frustrating situation when viewing down ‘dead end’ aisles. When vehicles are being driven along a one-way-flow aisle it has been observed that they tend to keep towards the centre and so, for right-hand-drive cars, drivers will be biased to the right-hand side of the aisle. This provides them with a better viewing angle to observe the status of stall openings and crossways on the left than those on the right. For twoway-flow aisles the situation is reversed. The shallower the parking angle becomes, the less significant this becomes and at angles less than, say, 608 the condition does not occur. It is not a major factor but it is useful to know that stalls and crossways on the left are more appreciated when in one-way-flow facilities and the opposite situation occurs when in two-way-flow facilities.

3.2 Parking categories

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3.2.1 Discussion The correct choice of circulation layout and stall dimensions to suit a particular building purpose can be an important factor in the success or failure of a parking facility. At main transportation terminals it is unlikely that the category will alter and car parks can be designed with confidence. For most other ‘town centre’ types, however, changes can and do occur, and this possibility should be considered at the design stage. Four categories of parking are described in the following section.

Car park designers’ handbook

3.2.2 Car park categories Cat. 1. Short stay. Intensive usage with high turnaround rates usually associated with busy supermarket-type shopping activities. Cat. 2. Medium stay. Urban-centre-type car parks for mixed business, visitors and town centre shopping. Cat. 3. Long stay. Located at major transport terminals where the flow is intermittent and mainly light but continuous. Short periods of intensive vehicle movement can also occur when a large people-transporter disgorges its passengers. Cat. 4. Tidal, such as occurs in staff car parks where the traffic flow is inwards in the mornings and outwards in the evenings.

3.3 Parking stalls

3.3.1 Discussion It has become normal practice in the UK for designers to adopt stall widths of between 2.300 m and 2.500 m, dependent upon the parking category. For specific purposes this can vary, but it must be appreciated that stall widths are an important factor, affecting both flexibility and market values. The prime consideration is not so much the overall width of a stall but the gap between parked vehicles. Altering the pitch by 100 mm only has a 4% effect on the stall width, but it can result in a 20% variation on the gap between cars and be the difference between getting out of the car with ease or with some difficulty. The minimum space that enables most drivers to access their vehicles is considered to be 600 mm. Most vehicles are narrower than the SDV, so for a stall width of 2.400 m the gap between cars will usually be greater than 600 mm. It is also the case that some drivers are not particularly mobile, while others can be rather large and need a greater door opening distance than 600 mm. In Fig. 3.4 it can be seen that the full door opening width is about 900 mm, resulting in an optimum stall width of 2.700 m. Averaging between large and small vehicles, a 2.600 m wide stall could also produce a gap of about 900 mm, but then economic factors come into play. The compromise answer is shown in Section 3.3.2 and has been generally recognised over many years as an acceptable balance between space and cost. 3.3.2 Recommended dimensions for differing parking categories All stall lengths 4.800 m Minimum stall widths Cat. 1 (less than 3 hrs per car) 2.500 m Cat. 2 (more than 3 hrs per car) 2.400 m Cat. 3 (more than 12 hrs per car) 2.300 m Cat. 4 (staff type) 2.300 m Disabled drivers 3.600 m Carers 3.200 m It should be appreciated that the market value of the building could well be affected by the choice of stall width. Stalls less than 2.300 m in width cannot be recommended for general public use. In specific locations, stall widths of 2.200 m and even 2.100 m have been used where there is a desperate need, such as hotel- or staff-type parking where smaller cars are the norm and the client is fully aware of the reduction in parking standards. 3.3.3 Obstructions between stalls The standard stall widths assume that there are no obstructions between adjacent stalls and that car doors can open freely into the spaces between

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Fig. 3.4 The standard design vehicle (SDV) (a composite of 95% of private vehicles registered to drive on the highways)

parked vehicles. It also assumes that drivers and passengers can pass between adjacent cars to gain access to the traffic aisle. If obstructions, such as structural columns, occur between stalls (see Fig. 3.5a and b), the recommended widths should be capable of being measured between the column faces, at the very least. Where long rows of stalls occur between wall faces, it is not usually necessary to increase the end stall widths as a high proportion of cars are smaller than the SDV and they can park without difficulty at these relatively few locations. 3.3.4 Angled parking Angled stalls ease the parking manoeuvre. The shallower the angle, the easier and simpler it is to park. It is generally restricted to one-way traffic flows and as the parking angle reduces so can the aisle width necessary to manoeuvre in and out of the stalls: in so doing, however, the people/vehicle separation distance is reduced and the floor area per stall requirement is increased (see also Fig. 3.6 and Sections 3.4.3 and 5.5).

3.4 Aisle widths 3.4.1 Discussion Aisle widths can vary dependent upon the traffic flow pattern and the parking angle. The dimensions shown in Section 3.4.4 are adequate for manoeuvring into and out of parking stalls but no allowance has

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Fig. 3.5 Columns located between adjacent stalls

been made for pedestrians mingling with car traffic on the aisles. With 908 parking a 6.000 m-wide aisle enables pedestrians to walk down a 2.000 m-wide lane on each side of a centrally located vehicle, alternatively pedestrians can walk down the central part of the aisle and cars can drive by on either side. When 458 parking is adopted, for vehicle manoeuvring, the aisle width can be reduced to 3.600 m, but in so doing the space available to pedestrians reduces to 800 mm on each side of a centrally located vehicle. In such cases, designers should consider whether some upward dimensional adjustment is desirable, especially in facilities subject to intensive use. Sixty-degree surface parking, incorporating widened, two-way flow aisles, has been noted in some of the south-western states of the USA. In such cases the stalls have been angled such that parking can only, realistically, be achieved on one side at a time. The stall search pattern is greatly extended and the only advantage appears to be in increasing the separation distance between vehicles and pedestrians on the aisles. 3.4.2 One-way-flow with reduced aisle widths Figures 3.14a and 3.14b (see page 19) show the entry envelope for 2.400 m-wide stalls. It can be seen that an aisle width of about 6.000 m is required for ‘straight in’ parking. Increasing the stall width enables drivers to manoeuvre in and out more easily and can result in a reduction in the width of the aisle without reducing parking standards. Figures 3.14c and 3.14d (see page 19) show the reduced aisle widths that can be used for 2.500 and 2.600 m-wide stalls.

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3.4.3 Two-way-flow with reduced aisle widths When the anticipated traffic flow is ‘tidal’, such as occurs in facilities dedicated to office staff, two-way-flow layouts have been used successfully with aisle widths little more than those recommended for oneway-flow circulation. Consideration, however, should be given to the possibility of future changes in parking use that could affect the continued effectiveness of the building.

Fig. 3.6 Comparison of the deck area per stall for three angles of parking (exc. ramps and access-ways)

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3.4.4 Manoeuvring on aisles Recommended minimum aisle widths (2.400 m-wide stalls): 908 with two-way-flow 908 with one-way-flow 808 708 608 508 458 908 with one-way-flow. 2.500 m wide stalls 2.600 m 2.700 m

7.000 m 6.000 m 5.250 m 4.700 m 4.200 m 3.800 m 3.600 m 5.800 m 5.650 m 5.500 m

It is not recommended that reduced aisle widths should be adopted as a general rule, but it shows that in extreme situations some dimensional flexibility is available to the designer. Where intensive use by pedestrians is anticipated (Cats 1 and 2), aisle widths of less than 5.000 m cannot be recommended, regardless of the parking angle. 3.4.5 Turning between aisles A factor to be considered is that as the parking angle decreases so, also, does the dimension available for turning between adjacent aisles. For 908 parking, the clear turning dimension overall two traffic aisles and the pair of stalls between them is 21.600 m, but at 458 it reduces to 15.684 m and is below the recommended minimum turning diameter (see Fig. 3.6).

3.5 Bin dimensions

3.5.1 Discussion Bin widths are the sum of the aisle width and the adjacent stalls measured normal to the aisle. With angled parking this dimension will vary, dependent upon the width of stall chosen. Where multi-span flat decks incorporate angled parking, bins on the external rows will differ in width from those on the internal rows due to the interlocking effect of the stalls. They will also differ from those bin widths generated by a single parking deck (see Fig. 3.6 and Section 3.13). 3.5.2 Recommended minimum bin dimensions for parking with 2.400 m-wide stalls (in metres) Angle Single External Internal o 90 15.600 15.600 15.600 80o 15.530 15.328 15.120 70o 15.362 14.952 14.540 14.914 14.314 13.714 60o o 50 14.240 13.469 12.697 13.782 12.939 12.085 45o For two-way-flow, the only logical angle is 908 and the recommended minimum bin width is 16.600 m.

3.6 Ramps and access-ways

Design elements

3.6.1 Discussion Cross-ramps and access-ways linking adjacent parking decks are one of the most important elements governing driver appreciation. If they are too narrow or too steep, motorists will shun the car park. The entrance should be of a width that will enable drivers of average ability to enter at 10 mph from the optimum position on an aisle without the need to make fine judgements on driving accuracy (see Figs 3.7–3.9). In the middle section, and where they exit into a wider traffic aisle, the ramp

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Fig. 3.7 The sidewall has been cut away in an attempt to improve the entry width into a 2.800 m-wide ramp

Fig. 3.8 Vehicle scrape marks on the outside wall of a 3.000 m-wide ramp

Fig. 3.9 Scrape marks occurring on the outside wall of a 3.600 m-wide ramp

Fig. 3.10 Shows a pair of 4.400 m-wide, open-aspect ramps

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can be reduced in width. After incorporation into a building, ramps are extremely difficult to move or alter. Under normal operational conditions it will, occasionally, be necessary for drivers to avoid other traffic and/or pedestrians and commence their turn from other than the optimum position on an aisle. In such cases, it should be possible to tighten the turning circle and still enter the ramp in one manoeuvre. The wider the ramp entry, the more flexible the aisle position can be (see Fig. 3.10). It is unrealistic and uneconomic to attempt to cater for the worst-case situation, but it is equally unrealistic to assume that the optimum location on an aisle will always be available. A clearance dimension of 300 mm should be incorporated on the outer side of aisles when establishing the turning dimension. It should be noted that, at the bottom exit from a ramp, the effect of a vehicle straddling the change of slope increases its vertical height above the deck. It is particularly important to check the headroom at this location. Modern vehicles should be able to negotiate inclines of up to 25% without difficulty and many such slopes occur on highways the world over. However, it is not just the incline that governs the limiting factors for car parks but the proximity of pedestrians and their safety, coupled with the daunting appearance that a steeply inclined ramp in an enclosed space presents to motorists. Recommended vehicle ramp gradients are not the result of precise calculation, but are generally considered to be those that most motorists will accept without undue resistance. Small variations to overcome local problems can be tolerated but, as a general rule, designers should be wary of increasing the recommended figures by any significant margin. The regulations for pedestrian ramps are based upon BS 8300, relating to places of work and residence wherein disabled persons can spend many hours per day. In such cases it is important that all consideration should be given to minimise the problems of getting around. In car parks, the only people remaining more than five minutes after parking their vehicle are employees and those with criminal intent. The others will have left to go about their legitimate business. Disabled pedestrians should be capable of negotiating slopes of 8% that raise half a storey, once, on their way to a lift and the building exit (see also Chapter 9). In many instances they must exit the building onto streets that slope far more than British Standards allow within buildings (see Fig. 3.11). It is to be hoped that, eventually, car parks will be recognised as a separate building type in this respect and treated accordingly.

Fig. 3.11 Hillside conditions occur in many car parks

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3.6.2 Recommended maximum vehicle gradients Straight and helical ramps Up to a maximum ramp rise of 1.500 m the steepest sloping element should not exceed 16%, reducing at the rate of 1% for each 250 mm increase in ramp height up to 3.000 m. (Above a ramp height of 3.000 m, the maximum sloping element should not exceed 10%.) Pedestrian ramps Less than 2 m going 2 m to 5 m going 5 m to 10 m going

8.5% 6.6% 5.0%

Fig. 3.12 Vehicle ramps with 1.500 m half-storey height

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3.6.3 Transitional slopes It can be demonstrated that a transitional length of 50% of the SDV wheelbase coupled with its ground clearance height of 100 mm can master a slope transition of up to 14% without ‘grounding’. Transition slopes smooth out the change from a ramp slope to a flat deck, but it can be argued that sudden slope changes help to deter speeding within a car park. 3.6.4 Ramp projections into aisles Figure 3.12a shows the shape for a ramp rising 1.500 m, that agrees with clause 4.3.7 of the Des Recs. Transitional slopes having a minimum length of 3.000 m result in a 1.200 m projection into the aisle. At the foot of the ramp, the resulting wedge will be 100 mm high and where scissors-type ramps occur, the step between adjacent ramps will be 200 mm. Figure 3.12b shows the ramp shape required when the aisle projection is restricted to 600 mm and the transitional slope reduces to a length of 1.800 m (still better than 50% of the wheelbase). Although this does not conform strictly to the Des Recs, it is a perfectly acceptable option that occurs in many existing car parks and is less intrusive that that shown in Fig. 3.12a. Figure 3.12c shows a ‘three-slope’ ramp where, at the bottom, a maximum slope change of 12% occurs. This option enables the ramp projection to be omitted altogether when the storey height is less than 2.900 m. Steps of more than 50 mm are awkward to ‘feather’ out without interfering with adjacent stall entries and they create obstructions to pedestrians pushing loaded shopping or luggage trolleys. For good practice, ramp projections into an aisle should not exceed 600 mm in length and 50 mm in height. 3.6.5 Storey height ramps Figure 3.13a shows the ramp shape for a straight 10% slope between storey heights of 3.000 m. The recommended ‘going’ is 30.000 m and if used in a flat with internal ramps (FIR) 1 type layout it will project 2.400 m into the aisle on each side. Buildings of the FIR 1 type have been successfully constructed for many years without obvious complaint from motorists. It is impractical to intrude 2.400 m into an aisle and so another solution must be found if FIR-type layouts are not to be deemed unacceptable. Figure 3.13b shows the ramp shape where the aisle projection is restricted to a maximum of 600 mm. The slope is 11.36% and this increase above 10% should not prevent the use of such a ramp. Figure 3.13c shows a ‘conforming’ ramp where the storey height has been halved and a 4.400 m-long landing has been introduced. It is, in effect, a pair of three-slope ramps end connected at the landing level where the maximum half rise does not exceed 1.500 m. The ramp intrusion into the aisle is eliminated. A three-slope ramp, however, is more awkward to construct than a mono-slope ramp and will be a little less popular with motorists. It is to be hoped that common sense will prevail and a Fig. 3.13b slope will become the accepted solution for this situation. 3.6.6 Side clearance Minimum clearance dimensions of 300 mm should be provided on each side at the entry location into a cross-ramp or access-way.

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Fig. 3.13 Vehicle ramps with 3.000 m storey height

3.6.7 Manoeuvring envelope Figures 3.14, 3.15 and 3.16 show the manoeuvring envelopes (ME) for differing widths of ramps and crossways. The hatched area of the ME shows additional manoeuvring ability based on a 6.000 m-radius turn and cannot be over-run without making a reverse manoeuvre. Between the boundaries, motorists are able to decide on the route they will take and choose an appropriate rate of turn. The ME shows the degree of flexibility that an SDV motorist has when turning into a particular width of stall, ramp or access-way. Designers fitting, say, a car park into a basement, where the disposition of the structure may not be compatible with parking layout requirements, may have to compromise

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Car park designers’ handbook

Fig. 3.14 Stall access manoeuvring envelopes based upon 6.000 m-radius turns (read in conjunction with Section 3.6.8)

Fig. 3.15 Ramp access manoeuvring envelopes based on 6.000 m-radius turns and one-way traffic flows (read in conjunction with Section 3.6.8)

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Fig. 3.16 Ramp access manoeuvring envelope (read in conjunction with Section 3.6.8)

on preferred parking dimensions. It is useful to know the limits of the manoeuvres that can be made. 3.6.8 Stall access Figure 3.14a shows the ‘envelope’ for access into a stall where the adjacent stalls are unoccupied. Drivers are able to overlap the upper stall and it shows that most vehicles can drive down the middle part of a traffic aisle, avoiding pedestrians and still gain direct access into stalls located on either side. Figure 3.14b shows a 6.000 m radius turn into a stall located between adjacent occupied stalls. Such a tight turn is acceptable for a single manoeuvre and, with most vehicles being smaller than the SDV, motorists can successfully keep within the limits of the ME without reaching their vehicles’ limitations. Figures 3.14c and 3.14d show that, without reducing parking standards, a reduction in the width of an aisle can be effected when wider stalls are used. It should be appreciated, however, that where clear span structures are involved and reducing stall widths is simply a matter of painting lines, future changes in the parking category could affect market values. When turning into a standard width stall, the aisle position is critical and an overshoot of more than, say, 200 mm will result in reversing manoeuvres being required. The wider the stall, the easier that this manoeuvre becomes. 3.6.9 One-way-flow ramp widths: discussion Figures 3.15a and 3.15b show the entry width into the ramps measured from the face of the aisle. Ramp projections can vary and, therefore, have not been shown. Designers should consider the effects that projections, steps and angled approaches will have upon the layout. Circulation efficiency is also dependent upon the appearance that ramps present to the oncoming motorist. If constructed between solid sidewalls, even ramps of an adequate width are less inviting to enter and drivers will tend to be more cautious when compared with those where lateral vision is unimpeded (see Figs. 3.17–3.20).

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Figure 3.15a shows the manoeuvring envelope (ME) required to negotiate one lane of a pair of scissors-type ramps located between three parking stalls, the clear width between wall faces is 3.300 m. The lower lane will be a repeat of the upper lane and has been omitted for clarity, but the potential conflict between adjacent vehicles at the exit with both turning in the same direction can be easily appreciated. A 6.000 m-radius turn is needed to access the crossway that can be improved to 7.500 m on the exit. The turns are totally inadequate for a ‘user-friendly’ car park, although they might be acceptable in some private facilities where small cars are the norm. Figure 3.15b shows the envelope required to negotiate a single ramp within a width of two parking stalls (4.800 m). The clear dimension between wall faces is 4.400 m and clearances of 300 mm have been incorporated on each side. A successful entry can be made with a 9.000 mradius turn on both the entry and exit. The dynamic efficiency is high with vehicle speeds of 10 mph capable of being maintained throughout the turn. The upper shaded area shows the amount of over-run available and yet still effect an entry/exit in a single manoeuvre. The lower shaded area indicates the aisle width available to drivers to achieve an entry or exit as a single manoeuvre. As ramp widths increase, the aisle entry width also improves and at 6.000 m drivers can enter from virtually the complete width of an aisle. This will be highly popular, but the width of the Fig. 3.15b ramp is an acceptable compromise and is space efficient. When ramp widths are excessively wide, drivers can angle their vehicles as they exit onto the traffic aisle, rendering it more difficult to observe converging traffic, especially when the passenger seat is occupied in a right-turning circulation system. Excessively wide ramps and crossways can have a detrimental effect upon dynamic efficiency. One-way-flow ramps with 908 parking. Recommended clear widths between faces of structure. Upper limit Minimum for good practice Absolute minimum Straight ahead ramps

5.000 m 4.200 m 3.600 m 3.000 m

3.6.10 Ramp widths and angled parking Where angled parking is adopted and the entry or exit does not involve a right-angled turn, some reduction may be accepted to the recommended figures, but the designer must consider the absolute necessity for such an action and the tolerance of the motorist who will use the facility. In any case, the minimum ramp width should never be less than 3.000 m. 3.6.11 Two-way-flow ramps Two-way-flow ramps are generally designed three stalls wide (7.200 m), resulting in a clear width of about 6.800 m. They are used when it is desirable to achieve maximum static efficiency, mainly when the traffic flows in either direction are ‘tidal’ or not intensive. They are not recommended for large Cat. 1 or 2 layouts but, when used in Cat. 4 layouts (staff parking type), they can be very effective with the traffic capable of using the full ramp width on entry (a.m.) and on exit (p.m.). For this reason, painted lines are preferable to dividing kerbs. Even for the tightest of turns and the most advantageous of positioning, when two vehicles approach each other on the ramp, they are in danger of

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Fig. 3.17 A two-way-flow ramp

colliding at the exit and entrances. It is difficult for turns to be made without straying into the opposing lane (see Fig. 3.16). 3.6.12 Turning circle templates Swept paths for the recommended minimum (9.000 m radius) 908 and 1808 SDV turns are shown in Fig. 3.18 to a scale of 1:200. They can be photocopied to an appropriate scale and used for checking purposes. 3.6.13 Two-way-flow: recommended minimum clear ramp widths Preferred 6.800 m Absolute 6.500 m 3.6.14 Scissors-type ramps These ramps are generally designed to fit, in pairs, between three stall spaces in a one-way-flow circulation system. Having an overall width the same as a two-way-flow ramp but with a central supporting structure, the resulting individual widths will be below the recommended absolute minimum of 3.600 m. Nevertheless, they have been, and are still being, used in a number of buildings, mainly of the smaller ‘private’ type where the majority of vehicles can turn more tightly than the SDV (see SLD 3 later in chapter 7, see page 48). 3.6.15 Side-by-side ramps A fundamental problem occurs where traffic on both ramps (one climbing and one descending) arrive at the same deck level side by side (similar in appearance to scissors ramps) and turn in the same direction resulting in conflict between drivers. If intended for the larger (300þ) public car parks, there should be a minimum of two stall spaces located between them. 3.6.16 Circular ramps These are less popular with the parking public than straight ramp circulation systems. One of the reasons for this may well be due to the fact that many have been constructed to a smaller diameter than the motoring public is willing to accept. There is a considerable difference between a vehicle’s minimum turning circle and the minimum turning diameter that the average motorist will tolerate when committed to driving through one or more complete spirals. A ‘wall of death’ type sensation can occur in drivers when exiting through several floor levels in a tight turn. The recommended minimum diameter, given in Section

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Fig. 3.18 9.000 m-diameter turning circles

Fig. 3.19 Scissors-type ramps

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3.2, of 18.000 m when turning on routes with straight aisles and crossramps, is not an appropriate dimension for circular ramps rotating through 3608 or more. The constant turning and the inability for drivers to see any reasonable distance ahead renders greater diameters desirable if they are to be readily accepted by the motoring public. It has been noted that in at least one car park of the SD 2 (sloping parking deck) type a small-diameter rapid exit ramp has been abandoned and the car park converted to an SD 1-type operation, even though the aisles were not designed originally for two-way traffic flows. 3.6.17 Recommended minimum diameters for full circle ramps between limiting wall faces One-way flow For good practice 24.000 m Absolute 20.000 m Two-way flow For good practice 31.000 m Absolute 27.000 m 3.6.18 Recommended minimum widths for circular ramp lanes between wall faces One-way flow For good practice 4.400 m Absolute 3.800 m Two-way flow For good practice 7.800 m Absolute 7.200 m

3.7 Interlocking ramps

3.7.1 Stadium type Where lengths of straight ramp connect semi-circular ramps, drivers can relax on the need for constant turning. Compared with continuous circular ramps they appear, visually, to be more spacious and hence less daunting. It has been noted that they remain acceptable to the driving public even when the diameters of the circular ends are somewhat below those recommended for full circular layouts. When the ‘going’ for a 3608 rotation is better than about 56.000 m, another ramp, flowing in the opposite direction, can be inserted within the same plan form and can be a space-saving way of achieving access to a parking level located above commercial or retail premises (see ER 5 in chapter 7, see page 148). 3.7.2 Circular type At a diameter of 24.000 m, a 9% gradient on the ramp centre-line produces a rise of about 5.600 m for each 3608 rotation. In the same manner as for a stadium-type ramp, another ramp can be introduced. When used in the ‘interlocking’ mode they take up less site area than a pair of circular ramps or a single, two-way-flow circular ramp (see ER6 in chapter 7, page 150).

3.8 Kerbs

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Kerbs, historically, separate pedestrians on footpaths from vehicles. Pedestrian ramps should not exceed a slope of 5% while vehicle ramps can slope up to 16%. Kerbs down the sides of vehicle ramps, therefore, are not intended for pedestrian use but provide a warning to motorists that the turning vehicle is getting close to a wall. The problem is that some pedestrians will see them as an invitation to access an adjacent parking level and use them accordingly. If kerbs are to be used, they should be of a width that does not encourage pedestrian use (not more than 600 mm wide).

Car park designers’ handbook

If the ‘preferred’ minimum dimensions for car parking are observed, then the provision of kerbs may well be unnecessary and pedestrians will not be tempted to use them. It must be left to each designer to make a decision in this matter. Many car parks have been constructed without kerbs and operate successfully. The provision of a kerb between lanes on a two-way-flow aisle is an option that is necessary only when cars are travelling on the right-hand side of the ramp. When cars are driven on the correct side of a two-way ramp, the situation is little different from that of a circular car park, where lane-dividing kerbs are not used because access to the stalls is required from either side.

3.9 Super-elevation

Super-elevation of circular ramps is not a necessary feature in car parks where the maximum recommended speed does not exceed 10 mph.

3.10 Parking deck gradients

Where cars are parked sideways on a sloping deck, the maximum gradient should not exceed 5%. For pedestrians who also use the deck further restrictions may apply (see page 203). Cars can be parked successfully on much steeper sideways slopes, but the effect of gravity on the opening and closing of their doors is a factor limiting the slope for use by the general public.

3.11 Headroom and storey heights

Headroom dimensions are often a compromise. They are frequently controlled by building height limitations for a particular site, coupled with the desire to incorporate as many parking levels as possible. Vertical circulation is a function of the storey height, the greater the dimension the longer and/or the steeper the ramp slopes become. In order to contend with the height of modern vehicles, the minimum clear headroom throughout a parking building, measured under all light fittings, hanging signs and structure, should not be less than 2.100 m. It should be checked, especially at the bottom of ramps, where the wheelbase spans the change in slope and increases the apparent height of the vehicle. It is important to predetermine the effect that down-standing light fittings and signs may have on headroom, particularly where flat soffits are involved, and also where ventilation ducts, fans and sprinklers occur in facilities constructed below ground level.

3.12 Height limitations

Height limitation gantries should be located at the entrance to every car park (see Fig. 3.20) to prevent oversized vehicles from entering. They should be brightly painted and indicate clearly the maximum height of the vehicle allowed to enter the facility.

Fig. 3.20 A height limiter

Design elements

25

4 Dynamic considerations

4.1 Discussion

Dynamic capacity and efficiency is a measure of the rate at which traffic can pass any designated location, traffic aisle or even a complete circulation layout within a car park, and enables potential bottlenecks to be identified. It can indicate the limitations of a particular layout and the need for change or improvement by the incorporation of by-pass routes or other special features. 4.1.1 Impact speeds Calculations for the impact resistance of structural elements within a parking facility are based on a vehicle speed of 10 mph, (BS 6180 and 6399) and should be assumed as the maximum permitted speed in any car park. 4.1.2 Effects of rain In surface-only car parks and on the open-top decks of multi-level facilities, wet and slippery conditions will occur from time to time. In such situations, drivers will be more cautious and dynamic capacities will be reduced. If a surface car park is operating at maximum dynamic efficiency when conditions are dry, it is likely that traffic congestion, queuing and delays will occur when it rains. For a structured car park, a covered roof may solve the problem. Designers should take these factors into consideration. On average, in the UK, rain occurs on one day in every three. 4.1.3 Exit and entry rates and internal movement Calculations for dynamic capacity should be checked against figures for the anticipated hourly vehicle movements but, in the absence of such information, it is generally accepted that 25% of a car park’s static capacity should be able to enter or leave within a 15-minute period. Short-term parking at busy supermarkets and major retail outlets builds up steadily from about 8 a.m., with peak activity occurring between 10 and 12 a.m. By that time, early customers are beginning to leave and others are slowing down to search (and sometimes wait) for spaces in a favoured location, e.g. adjacent to a lift or shopping access lane. The effect that pedestrians, some with prams and others with shopping trolleys, have upon traffic movements has not been thoroughly investigated, but it has been observed that, in facilities where this occurs, dynamic capacity can be affected adversely to varying degrees, dependent upon the parking standards encountered. Figures on dynamic capacity, proposed in RRL Report LR 221, are based on the assumption that an aisle fills in a logical manner, starting at the beginning and finishing at the end, with no cars leaving as it fills, no cars arriving as it empties and no pedestrians on the traffic aisles. This report formed part of the first edition of the 1976 Des Recs but was omitted from subsequent editions. Observations made in a number of car parks indicate that the RRL figures for dynamic capacity can be applied, within reason, to Cats. 3 and 4 car parks. For the others, however, there is evidence that a reduction may be justified. Where two-way-flow aisles are used, an additional problem can occur when vehicles, entering and leaving stalls, cross the oncoming lane and

26

interfere with traffic travelling in the opposite direction. When occurring in facilities with mainly tidal flow, dynamic capacity will be similar to the figures provided for one-way traffic flows, but for short stay, intensive-use facilities it is affected adversely. In large car parks, the build up of traffic from successive upper parking levels can be greater than the dynamic capacity of the lower levels of an exit ramp. It must also be appreciated that, if the exit control or external road system is unable to cope with the flow rates, traffic congestion will occur within the car park, regardless of any other factor. 4.1.4 Dynamic capacities for different stall widths and categories The figures given are averaged out from the result of observations made, over 15-minute periods at peak times, in a number of car parks. The variations between them were such that precision is not a factor. They are, however, considered to be a conservative but realistic assessment. The variations between different car parks are attributed mainly to the dynamic efficiency of the individual layouts. Staff parking tended to be more rapid than the other types and it proved impossible to obtain meaningful 15-minute figures from Cat. 3 long-stay car parks. The difference between the inflow and outflow figures can be explained by the fact that most motorists can turn and drive straight into a stall but, when exiting, a more hesitant reversing manoeuvre is involved. A small proportion of drivers, however, reverse into the stalls in order to drive straight out. Notional figures for all parking categories with 6.000 m-wide aisles 2.300 m 2.400 m 2.500 m

Inflow 820 860 910

Outflow 710 750 800

4.1.5 Stopping distance An extrapolation of the stopping distance, given in the Highway Code, for cars travelling at 10 mph on dry roads, is about 6.000 m. Designers must be aware, however, that wet, exposed decks can double the stopping distance. 4.1.6 Speed limits There are no national regulations governing vehicle speeds within a car park, but it has become established practice to adopt the same speed that the structure must be designed to withstand (10 mph). Some authorities, however, are now proposing speed limits of 5 mph. If adopted nationally, the traffic flow numbers used in dynamic design for aisles and ramps should be reduced accordingly: congestion will occur at a much lower figure than the recommended maximum search path of 500 stalls (Des Recs, 4.4.7) and should be adjusted downwards. Dynamic design has, historically, been based upon speeds of about 10 mph and the figures for inflow and outflow given in Section 4.1.4 are based upon observations made in car parks where traffic has not been restricted to 5 mph. It is unrealistic to impose lower vehicle speeds and yet still expect the original circulation efficiency to be achieved. 4.1.7 Dynamic capacities of ramps and access-ways At a maximum speed of 10 mph, keeping the correct stopping distance between vehicles and assuming that all vehicles are the same length as

Dynamic considerations

27

the SDV, it can be calculated that the unobstructed vehicle rate should not exceed about 1450 vehicles per hour (vph). Many cars, however, are shorter than the SDV and a more realistic figure can be based upon an average vehicle length of 4.300 m, in which case the allowable figure rises to about 1500 per hour. It would be imprudent to design a car park using flow figures that are greater than those developed from conforming data. Designers should be able to demonstrate that they did not use figures that relied upon motorists driving in excess of the maximum ‘recommended’ speed. The rate of entry into a cross-ramp or access-way depends upon its width and the appearance it presents to the motorist. Above a clear dimension of 4.200 m, the 1500 vph rate does not appear to be affected, but, as the entry width reduces, drivers become more cautious and tend to slow down as they turn. The situation is also exacerbated by sidewalls, or other visual obstructions (see Figs 3.5, 3.7–3.9). Observations of the effect that ramp widths have upon motorists, indicates that, when they are driving on ramps free of lateral obstructions to vision, the following dynamic capacities can be recommended. 4.1.8 Dynamic capacities of cross-ramps and access-ways, per hour >4.200 m wide 1500 3.600 m wide 1200 Straight entry ramps 3.000 m wide 1500 Under 3.000 m wide, no information is available, but it is reasonable to assume that a progressive reduction will occur down to about 2.700 m when most drivers will refuse to enter. In some large-capacity, short-stay facilities the exit rate could exceed the traffic capacity of the external road system. It is often prudent to check this condition before reaching a final decision on the design. 4.1.9 Dynamic capacities of parking decks; calculations From 4.1.4, the notional dynamic capacity of a 6.000 m-wide aisle can be seen to be 860 and 750 vehicles per hour, respectively, for inflowing and out-flowing traffic. The dynamic capacity of the ramps is constant at 1500 vehicles per hour. The calculations are based upon the premise that, without parking traffic, it would be possible for 1500 vehicles per hour to progress on the traffic aisles at 10 mph, regardless of the length of travel. The parking of cars, however, will reduce this speed and, hence, dynamic capacity, dependent upon the number of stalls involved. A very few stalls will have little effect, but a large number could slow down the flow rate to a figure approaching that given for the notional dynamic capacity. Regardless of aisle length and capacity the one-hour flow rate cannot be less than that given in 4.1.4 or greater than that given in 4.1.8. It can be expressed by the formula: Actual dynamic capacity (ADC) ¼ 1500
ða  b  c  1=dÞ where a is 1500 minus the notional dynamic capacity, b is the number of flanking stalls divided by a, c is the number of aisles, d is the stall turn-over rate. Example Calculations for a Fig. 4.1, Cat. 1-type layout with 2.400 m-wide stalls, four storeys (ten aisles) and a 1.5 hour stall turnover.

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Car park designers’ handbook

Fig. 4.1 A Cat. 1, SLD 2 car park

Inflow Aisle 1, Level 1 (36 stalls) ADC ¼ 1500
ð640  36=640  1  1=1:5Þ ¼ 1476 vph At the end of the inflow route, having passed through ten aisles, ADC will be reduced by 240 to 1260 vph. For outflow routes, the calculations need to be made from the top deck down. Outflow Aisle 10, Level 5 (12 stalls) ADC ¼ 1500  ð750  12=750  1  1=1:5Þ ¼ 1490 vph At the end of the exit route, having passed through ten aisles the ADC will have reduced to 1400 vph. Although this is a small example, it can be appreciated that when much larger facilities are involved, and aisles need to be driven through more than once, the calculation can be used to determine where congestion is likely to occur and where an alternative route can be used to advantage. 4.1.10 Dynamic efficiency Angled parking is more efficient, dynamically, than right-angled parking when both incorporate stalls having similar dimensions. As the angle reduces so the stalls become easier to enter and leave, and it becomes increasingly difficult for cars to turn against the traffic flow. This improvement results, generally, in a reduction in static efficiency, a narrowing of the aisles wherein traffic and pedestrians mingle and a reduction in the distance available for turning between the outside faces of adjacent aisles. There is a case for parking at angles down to 708 on the internal bins in a multi-bin configuration (Table 5.3) where the static and dynamic efficiency is slightly superior to that required for 908 parking. It must be remembered, however, that as the parking angle reduces the stall pitch increases and this could be detrimental to the static capacity of a facility with a fixed overall length.

Dynamic considerations

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5 Static considerations

5.1 Static efficiency, discussion

The static efficiency of a car park is a function of its static capacity and the area of the parking decks. It is used as a means of comparison between parking facilities and is couched in general terms such as good, average or poor. Large-capacity decks, where the ratio of parking spaces to total floor area is high, will produce better figures than smallcapacity facilities, where a higher percentage of the parking decks is given over to ramps and access-ways. However, the terms are relative to the most efficient layout that can be achieved for any particular deck capacity (see Fig. 3.6 and Section 3.4). For example, a 300 space per deck layout requiring 28 m2 for each car space can be described as Poor, since it is possible to achieve a figure of 20 m2 with an efficient layout. Conversely, a 30 space per deck layout requiring 28 m2 for each car space can be described as good, since it is about as efficient as it is possible for it to get.

5.1.1 Relative efficiencies A long, two-bin layout has a greater static efficiency than a shorter three- or four-bin layout of a similar floor area, due to the reduction in the number of access-ways required for access between adjacent stalls, each of which takes up the space of four stalls at the ends. It can be a useful consideration when deciding upon the layout for a new car park. Floor area requirements for different angles of parking, as a ratio compared with that for 908 parking, are provided in Tables 5.1, 5.2 and 5.3. They are based on stall widths of 2.400 m and one-way traffic flows (see also Fig. 3.6). Column A shows the pitch of the stalls in metres. Column B shows bin width dimensions. Column C shows the percentage area variation. Two-way-flow layouts can only be used sensibly with 908 parking. Table 5.1 Single bins Angle

A

B

C

908 808 708 608 508 458

2.400 2.437 2.554 2.771 3.132 3.394

15.600 15.530 15.362 14.914 14.240 13.782

100.0 101.0 105.0 111.0 119.0 125.0

Table 5.2 External bins

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Angle

A

B

C

908 808 708 608 508 458

2.400 2.437 2.554 2.771 3.132 3.394

15.600 15.328 14.952 14.314 13.469 12.939

100.0 100.0 102.0 106.0 112.0 117.0

Table 5.3 Internal bins Angle

A

B

C

908 808 708 608 508 458

2.400 2.437 2.554 2.771 3.132 3.394

15.600 15.120 14.541 13.714 12.697 12.085

100.0 100.0 99.0 101.0 106.0 110.0

Compared with the area for one-way-flow 908 parking, the (column C) figure for two-way flow is 106.4%. 5.1.2 Area per car space As a guide, the floor areas per car space that can be termed ‘good’, for five different deck capacities with 908 parking, including a reasonable allowance for stairs, lifts etc. are shown in the following table. 300 stalls per deck 200 stalls per deck 100 stalls per deck 60 stalls per deck 30 stalls per deck

20 m2 21 m2 22 m2 24 m2 28 m2

For angled parking, these can be multiplied by the column C figures shown in Tables 5.1, 5.2 and 5.3. Significant variations can occur, especially where awkward shaped sites are involved and the figures should be used as no more than a guide to the areas per vehicle space that can be achieved under suitable conditions. 5.1.3 Recommended capacities For good practice, the maximum static capacities of various car parks having circulation efficiencies better than 60% should be of the following numerical order. Parking categories 1 and 2 Combined one-way flow SLD 1 type 400 spaces Two-way flow SLD 3 type 600 spaces Extended one-way inflow route with a separated rapid outflow route VCM 1 type 800 spaces Extended and rapid inflow route with a separated rapid outflow route VCM 1 type 1100 spaces Flat decks with half external rapid outflow routes HER type 1200 spaces Flat decks with fully external ramps FER type 1400 spaces Parking category 3 Long-stay, non-tidal ‘main terminal’-type car parks, where the traffic flow is not anticipated to reach the dynamic capacity of the traffic flow routes, need not be restricted in static capacity. However, rapid flow routes that enable drivers to reach any part of the layout within five-minutes should be incorporated.

Static considerations

31

Parking category 4 Tidal flow layouts have at least two peak vehicle movements per day. If it can be anticipated that the peak rates will not exceed 25% of the car park’s capacity over a 15-minute period, the Cats 1 and 2 figures can be used. Where layouts with circulation efficiencies less than 60% are considered, they can be compared with the 60% recommendations and their capacities reduced proportionally.

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Car park designers’ handbook

6

Circulation design

6.1 Discussion

Parking layouts are either inhibited or uninhibited depending on the influence that other disciplines have upon them. An inhibited layout is where parking has to fit between a predetermined disposition of vertical services and structure, such as the basement car park of an office building. In such situations, designers have little opportunity to develop a fully effective layout and must do the best that they can. An ‘uninhibited’ layout is one where the designer has a ‘clean slate’ on which to work; where the only limiting factors are those of static capacity and the dimensional restrictions imposed by the site. The layouts described in Chapter 7 are of this type. Surface car parks requiring a high static capacity will generally follow the tenets contained in Chapter 3, modified as necessary to follow the contours of the site and other geographical features. Such layouts are invariably ‘one-off’ designs and it is impractical to provide examples other than as general recommendations.

6.2 How many levels?

There is no technical limit to the number of suspended levels a structured car park can have, but it is generally accepted that six is a reasonable maximum for it to be freely accepted by the motoring public. Factors, such as the intensity of demand, availability of a suitable site and, of course, requirements of the relevant planning authority will also influence this decision. In the USA car parks have been constructed with more than 12 parking levels (see Fig. 6.1), although, on average, the number of floors in most buildings is not dissimilar to UK practice; there are no fixed rules in this matter and much depends on public demand, the skill of the designer and the tolerance of the motorist.

6.3 Roof considerations

Most car parks in the UK are open to the elements. Roofing over the top parking deck occurs in only a relatively few cases. There are arguments for and against protecting the top deck with a lightweight roof. .

.

.

.

A waterproof membrane on an exposed top deck will require substantial renewal – at least three times during a projected life of 60 years. It will also require expenditure on maintenance from time to time. A lightweight roof over a top parking deck will cost about three times more than that for a single application of a waterproof membrane and, without attracting significant maintenance costs, should last the life of the building. An open deck building can be constructed, initially, at a lower cost than a roofed-over car park and if the difference was invested, over a projected life of some 60 years, the overall costs will not be dissimilar. Where the overall height is limited and the static capacity needs to be as high as possible, it makes sense to utilise all of the available building height for parking and construct an open top parking deck. If inclement winter weather eliminates roof parking for a time, it will still have the static capacity of a roofed-over car park in that particular location.

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Fig. 6.1 A 12-storey car park in New Orleans .

6.4 Circulation efficiency

Where it is reasonable to construct a lightweight roof without reducing static capacity, the advantages are that the building remains dry at all times; the top deck parking is not weather sensitive, protection from the summer sun is provided and long-term maintenance costs are reduced, if not eliminated altogether. The building is also less prone to structural deterioration and will have an enhanced market value.

6.4.1 Discussion In some car parks, the circulation design enables most or all of the stalls to be searched with just one circuit of the aisles and access-ways. In other car parks, however, aisles must be driven through more than once to achieve a similar result. It is a factor worthy of consideration and affects dynamic efficiency, as well as parking times, especially in large-capacity, multi-bin layouts. It is a complex problem to solve precisely since much depends upon whether the car park is ‘empty and filling’, ‘full and searching’ or ‘full and emptying’. The use of ‘variable message signs’ also affects circulation efficiency, since they enable drivers to by-pass aisles that are full and drive more effectively to an available stall. The object is not one of precise assessment but rather one of establishing the relative circulation efficiency for one layout and comparing it with that for another. Provided that both are assessed in the same way, comparisons can be made without undue complexity. 6.4.2 Shortest travel distance The shortest travel distance possible, to pass stalls located on each side of a traffic aisle, is 2.400/2 ¼ 1.200 m per stall and can be equated to a circulation efficiency of 100%. It can only be achieved in a single-bin facility where motorists enter at one end and exit at the other. Where cross-ramps and access-ways are used to complete the circulation in multi-bin layouts, the circulation efficiency will be reduced and will vary dependent upon the chosen layout design.

6.4.3 Examples of circulation efficiency Example 1 Reference to the SLD 1 layout on page 44 shows that all 96 of the stalls on each deck, plus getting to the next upper storey, can be achieved with a single circuit consisting of four right-angled turns. Measuring along the centre of the aisles and access-ways the travel distance is: 52
2.400 m ¼ 132.800 m 2
15.600 m ¼ 31.200 m Total distance ¼ 164.000 m Divided by the number of stalls the travel distance per stall is 1.700 m producing a circulation efficiency of 1.200/1.700 ¼ 70%. Example 2 Reference to the FIR 1 layout on page 104 shows that three circulation options are available. Option 1 A single circuit, with four right-angled turns and climbing to the upper deck level, passes 58 stalls out of the 108 on each deck. It produces a circulation efficiency of 53% for the stalls passed and is only really suitable for getting quickly to the upper parking levels. Even so, that route is not very rapid. Option 2 To include the stalls on the central aisle will increase the number to 82, but entails driving twice through one of the aisles and making eight right-angled turns. The ‘efficiency’ of this route is 43%. Option 3 To cover all of the stalls on each deck, before driving up to the next level, involves passing twice through one aisle, three times through another and making 12 right-angled turns. The ‘efficiency’ reduces to 33%. It can be seen that motorists can spend up to twice the time searching for an available stall in the FIR 1 type layout than in an SLD 1 layout. Poor circulation efficiency is a major factor in creating traffic congestion and one of the main reasons why some car parks are less popular than others.

6.5 Parking times

Circulation design

6.5.1 Discussion Five minutes is about the maximum time that an average driver is willing to spend searching for a stall in which to park, beyond which dissatisfaction and frustration with the building begin to develop. They can be a factor in deciding a motorist’s future parking destination. There are reports of car lights left on, boot lids left open, even drivers who have left their car doors open with the engine still running in their panic not to miss an appointment or catch a plane or a train. Poor circulation efficiency and the frustration it causes can be a contributory factor in creating such situations. The decision whether to alter the layout or incorporate rapid inflow routes can be influenced by an assessment of the time it takes to search all of the stalls. In the absence of more accurate information it is normal practice to assume that the peak flow rate in either direction will be 25% of the static capacity in any 15-minute period. This rate can be applied, within reason, to most single- and multi-level parking layouts.

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The notional inflow capacity of an aisle with 2.400 m-wide stalls is 860 vph. This produces an average speed just under 6 mph (10 kph) or 3.000 m per second. However, the time spent on access-ways and ramps connecting adjacent aisles slows the average stall searching time to about 2.400 m per second. It is not a precise figure and so does not justify recalculation for minor differences created by varying stall widths. It should be used simply to establish the approximate times it takes to reach various parts of a car park and to compare the relative efficiencies of different circulation layouts. Application of the five-minute recommendation limits simple ‘follow my leader’ layouts, with circulation efficiencies better than 60%, to a maximum of about 600 spaces and correspondingly smaller capacities for less efficient layouts. If, however, a speed limit of 5 mph is adopted for any particular building, the vph figure should be reduced to, about, 360 spaces. In many large capacity layouts, mainly of the SLD and VCM series, rapid exit routes form part of the basic design, but rapid inflow routes can also be incorporated. Passing as few as 24 stalls for each storey height, the introduction of such routes enables drivers to by-pass congested lower decks and reach the emptier upper parking levels without exceeding the preferred maximum search time.

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Car park designers’ handbook

7

Circulation layouts

7.1 Discussion

Of the more than 5000 structured car parks believed constructed in the UK alone, it can be readily appreciated that no single person can have knowledge of every circulation layout variation that has been proposed and built. Practical considerations, personal experience and the constant pressures for financial economy render it reasonable to assume that the examples shown, all of which have been featured or built during the past 35 years, provide the basis for most of the self-parking buildings that exist at the present time. The design of a satisfactory circulation layout is one of the most important factors governing user appreciation and yet many designers are unaware of the large variety of options from which they may choose and their suitability for the intended purpose. The following examples are all practical layouts and form the basis upon which most self-parking facilities have been designed. Some are more popular than others and some are significantly defective in circulation design, static and dynamic efficiency. If designers are to gain confidence in developing solutions to solve particular problems, then it is desirable that they should know the strengths and weaknesses of individual layouts in order to make an informed choice.

7.2 Dimensions used

There are few precise dimensions that must be adopted for the design of parking structures. Dimensions for the individual elements can vary and are also affected by the parking angle (that varies the bin width) in one direction and the stall pitch (that varies the overall length) in the other direction. The main concern is that motorists and clients are content. It is overly laborious and unnecessary to keep mentioning all of the variations that can occur in practice and so dimensions for the featured layouts will be based upon those recommended for 908 parking with stall dimensions of 2.400 m  4.800 m, aisle widths of 6.000 m (oneway flow), 7.000 m (two-way flow) and a storey height of 3.000 m. In the layouts shown in the following pages, the overall aisle lengths are sometimes shown less than those given for the width; nevertheless, the length of the aisle will determine the ‘length’ of a layout and the dimension over the bins will determine its ‘width’.

7.3 User-friendly 7.3.1 Discussion There are many existing car parks where, in retrospect, it can be seen features that the layout would have been much better if only the designer had recognised that a problem existed. In such cases, if improvements had been incorporated at the design stage, they need not have cost more to implement or reduced static capacity. They could even have enhanced the market value by being more ‘user friendly’ to the parking public. It is, also, a relatively simple matter to spoil a potentially acceptable circulation layout by over complication, or by the introduction of unnecessary and unfriendly features. 7.3.2 Simplicity The basic tenet of all circulation design is to ‘keep it simple’. What, at first, might look like a clever idea to a designer could well end up as a

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motorist’s nightmare. In a structured car park the layout should endeavour to replicate the openness of a surface car park. To this end, it is desirable to eliminate, as far as possible, vertical structure that interferes, both visually and physically, with the free movement of vehicles and pedestrians. Turning directly from one lock to the other is not a popular manoeuvre. If possible all turns should be in the same direction and not more than 908 at a time. When located under other types of building, it is not always possible to create the most desirable layout. Attempts should be made to minimise the visual impact of large vertical elements and locate them away from the circulation routes, if at all possible. 7.3.3 Crossovers Crossover conditions should be avoided. When on a traffic aisle and searching for the first available space, it is disconcerting and potentially dangerous to find a car suddenly appearing at right angles from behind a parked vehicle. The driver of this car may also be concentrating on finding a space in which to park, or intent only on leaving the facility as quickly as possible. A user-friendly circulation layout should not hold surprises for drivers who should be able to observe the movements of other vehicles well before there is a need to take avoiding action. 7.3.4 Circulation direction The direction of circulation has little effect upon circulation efficiency in one-way-flow systems. Provided that the route is of an adequate width it matters little in which direction the traffic is made to flow. It has been said that left-turning circuits are not as popular in one-way-flow systems as turning to the right. However, when vehicles are travelling down the middle of an aisle drivers are biased to the right thereby providing a much better view of openings on the left. When a two-way-flow ramp occurs in a one-way-flow layout it is preferable to have a left-turning circuit whereby traffic drives on the correct side of the ramp. When entering a traffic aisle from a right-turning ramp, a front-seat passenger could obscure traffic approaching from the left, but when traffic approaches from the right the driver’s lateral vision is relatively unimpaired. Turning right onto an exit barrier enables a ticket to be inserted more easily into the acceptor machine than when turning to the left. When the entry/exit lanes are located side-by-side, right turning circuits are preferable if a crossover situation is to be avoided. None of these points are important enough to dictate the direction of flow by themselves, but it is useful to appreciate that they occur when considering the flow direction. 7.3.5 Dead ends (culs-de-sac) When viewing down a ‘dead-end’ aisle, it is difficult to see the parking situation more than three or four stalls away. For good practice, and if unnecessary manoeuvring is to be avoided, it should be the limiting factor.

7.4 Angled and right-angled parking: a comparison

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Members of the public and some clients, ask why angled parking is not used more frequently in the UK. They point out that it is popular in the USA and, for those who have used it, it is a popular parking format but, in the UK, layouts with 908 parking occur more often in towncentre car parks than any of the other types. Figure 7.1 shows a basic UK town-centre-type split-level layout with 908 parking. It is 28 stall widths in length with 96 stalls on each deck.

Car park designers’ handbook

Fig. 7.1 Angled and right-angled parking: a comparison

The area of the deck is 2096.6 m2 producing an average of 21.840 m2 per stall. Figure 7.1 also shows the same basic layout with 708 parking. It is 28 stall widths in length with 92 stalls on each deck. The area of the deck is 2196.8 m2 producing an average of 23.620 m2 per stall. The difference of 1.780 m2 per stall represents an increase of 8% in area and a consequent increase in construction costs. The 708 layout, at 71.512 m, is 4.312 m longer than the 908 layout, representing an increase of 6.5% in length while containing 4% fewer vehicles. The width at 30.724 m is 484 mm narrower than the 908 layout representing a reduction of 1.5%. The traffic aisles for the 708 layout at 4.700 m wide are 1.300 m less than those for the 908 layout, reducing the separation distance between vehicles and pedestrians on the aisles. If the stall widths in a 908 car park were increased by 8%, to 2.550 m, both layouts would be rendered similar in area and cost. In this eventuality, it is reasonable to ask whether 908 parking with 2.550 mwide stalls and 6.000 m-wide aisles would be more popular than 708 parking with 2.400 m-wide stalls and 4.700 m wide aisles? It is a question that can only be answered by designers and clients, individually. Widening the traffic aisles in the 708 car park will increase construction costs by about 0.6% for every 100 mm increase in width. As the parking angle reduces, so the building length increases and the aisle widths narrow even further. At a parking angle of 458, a 96-space

per deck building will need to be 95.000 m in length, (41% longer) and even with aisle widths reduced to 3.600 m, the car space requirement will be some 25% greater than for the 908 car park (see Section 5.1.1). A two-bin, split-level car park with 908 parking could increase its stall widths to 3.000 m, and retain its 6.000 m-wide aisles without exceeding the area per car space for a two-bin 458 car park with 2.400 m-wide stalls and 3.600 m wide aisles. In the USA, many structured town-centre-type car parks incorporate 908 parking. Stalls with 608 angles, widened aisles and a two-way traffic flow are sometimes used for retail shopping at surface level and 708 to 808 angles for large Cats 3 and 4 buildings of the SD and FSD series, SD 2, 3 and 4 being particularly popular in the southern and western USA.

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Car park designers’ handbook

Fig. 7.2 An SLD-type 2 layout

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Car park designers’ handbook

7.5 Split-level decks (SLDs)

Circulation layouts

Split-level decks (SLDs) are the most popular circulation layouts in the UK for multi-level urban car parks. They can be simple to drive around, and generally have a good static and dynamic efficiency (see Fig. 7.2). The combination of half storey-height internal ramps and flat bins enables some types to be constructed down to ten stall widths in length for two-bin layouts and eight stall widths for multibin layouts while still retaining a complete vehicle circulation and recirculation capability. In large-capacity facilities, rapid inflow and outflow routes can occur. They must, however, be introduced at the design stage if expensive alteration costs are to be avoided. They can be used with any angle of parking, although only right-angled parking can, sensibly, be used in conjunction with a two-way-flow circulation pattern. Normally the decks are constructed level and only incorporate drainage falls, in which case storey heights are dictated by the slope and length of the cross-ramps. When part, or all, of a traffic aisle is made to slope along its length, storey heights can be increased and/or the gradient of the ramps can be reduced. In this manner, a split-level layout can be gradually modified to become another circulation type. The point at which the transition from one type to another occurs can be assumed to be where the slope of the cross-ramps reduces to 5% (1 in 20) enabling them to conform to the requirements of the Building Regulations for pedestrian use (K1 Chapter 2 clause 2.1). Historically, because of their construction simplicity, circulation efficiency and ability to be constructed on small sites, an inherent defect caused by poor access for pedestrians between split levels has tended to be ignored. If they needed to cross over to an adjacent bin, pedestrians were expected to mingle with traffic on the steep vehicle ramps. Sometimes pathways were introduced down the ramp sides but, mostly, pedestrian considerations were ignored in the search to produce the most economical building in a highly competitive market. Gradually, car park operators and designers began to rectify this defect by introducing dedicated pedestrian ramps and/or stairs between the split levels. This, however, reduced static efficiency and increased costs. It was not a statutory requirement, however, and in a competitive market many car parks continued to be constructed without the benefit of this improvement. Current regulations relating to the maximum allowable gradient for pedestrian access between adjacent bins, the desire for enhanced security, supervision across the decks and the development of other, superior, layout types has rendered the split-level layout a less attractive proposition than it has been in the past.

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SLD 1 One-way traffic flow with an included rapid outflow route

SLD 1 One-way flow with an included rapid outflow route

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Car park designers’ handbook

Advantages . All of the stalls are located on the main inflow route. . Rapid outflow route. . All turns are in the same direction with no single turn greater than 908. . Simple recirculation capability. Disadvantages Both traffic flows combine on the outflow route, a condition that can result in traffic congestion in busy car parks. . Seven stalls per storey will be lost if a 5% pedestrian access ramp with steps is constructed between the split levels (see Fig. 8.2). .

Comments The inflow circulation is highly efficient. All of the stalls can be passed with just four right-angled turns per storey. However, traffic waiting to exit the car park must not be allowed to block the inflow route; in that event the car park will be unable to continue operating. . Large-capacity layouts for Cats 1 and 2 use have been noted where stalls on the outer side of the outflow route, on the lower deck levels, have been omitted in order to create an uncongested route for the inflow traffic resulting in a reduction of at least 12 spaces on each split level. . Static efficiency is good with only 16 stall spaces being required to complete the circulation routes. . The proximity of the up-coming inflow ramp to the down-going outflow ramp should not be closer than two stall widths if conflict between drivers is to be avoided. . The layout should operate satisfactorily for all parking categories up to a maximum of, about, 400 stalls. Above that number designers should become more cautious about using it for Cats 1 and 2 buildings. . In large-capacity car parks, dynamic efficiency could be increased substantially if a rapid inflow route was incorporated that enabled motorists to bypass the outflow route, especially on the lower parking levels. . If the aisle lengths are not too long, locating the main stair/lift tower at one end could eliminate the need for an internal pedestrian ramp. This would render it more efficient, cheaper to construct and make a significant improvement to its market value. . If circumstances change, the future market value of a Cat. 3 or 4 car park could depend upon its ability to operate in a different parking category. .

Static efficiency As drawn, the number of stalls is 96 and the static efficiency, at 21.840 m2 per car space, can be deemed, Good.

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Other layouts . For large-capacity layouts, an SLD 2 layout is dynamically superior. It will also be statically superior if a by-pass outflow route has to be installed. . A VCM 1 is as dynamically efficient as the SLD 2 layout and in not requiring a pedestrian ramp it is statically superior. The reduction of the split-level condition, also, renders it more user friendly and economical to construct.

Circulation layouts

45

SLD 2 One-way traffic flow with an excluded rapid outflow route

SLD 2 One-way-flow with an excluded rapid outflow route (2 four stalls wide; 2A three stalls wide)

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Car park designers’ handbook

Advantages . Rapid outflow route. . All turns are in the same direction with no single turn greater than 908. . Simple recirculation capability. . The inflow and outflow routes are separated, reducing the possibility of traffic congestion in busy car parks. . The internal ramps can be of the combined type (SLD 2A) in smaller capacity or non-intensive-use car parks, thereby improving static efficiency. Disadvantages Seven stalls per deck will be lost if a pedestrian ramp access with steps is required between split levels.

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Comments As drawn, the inflow circuit enables 80% of the stalls to be searched efficiently, with just four right-angled turns. Many of the remaining stalls can be seen and judgements made on whether to search on the outflow circuit. In practice, there is little extra search distance driven when compared with a similar capacity SLD 1 layout. . The separation of the two flow routes more than justifies any slight reduction in circulation efficiency, especially when used in Cats 1 and 2 layouts of a greater capacity than 400 stalls. . As the static capacity increases, the separated outflow route reduces the possibility of traffic congestion on the lower levels and so its relative efficiency improves. . The introduction of a rapid inflow route in large-capacity Cats 1 or 2 layouts enables motorists to bypass full or congested lower floors and make their way, rapidly, to emptier upper parking levels. . The layout is suitable for all parking categories where the capacity of the lowest aisle on the outflow route is not exceeded. . For Cats 1 and 2 uses, the recommended maximum stall capacity, when incorporating a rapid inflow route, is in the order of 1100 spaces. . Static efficiency is good with only 16 stall spaces per deck used to complete the circulation route. . For car parks of less than, say, 500 spaces and without intensive utilisation, a combined ramp can be considered, as shown in SLD 2A. This will improve static efficiency by two stalls per storey. . Given the choice of layout, two-bin width layouts will always be more efficient than those with three or more bins. .

Static efficiency As drawn, the number of stalls is 96 and the static efficiency, at 21.840 m2 per car space, can be deemed, Good.

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Other layouts . An SLD1 layout has a similar efficiency when used in smaller capacity car parks. . A VCM 1 layout is dynamically similar and the need for a dedicated pedestrian ramp between the split levels is eliminated. The flat across deck areas also renders them more user friendly and economical to construct.

Circulation layouts

47

SLD 3 One-way-flow with side-by-side ramps (scissors type)

SLD 3 One-way-flow with side-by-side ramps (scissors type)

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Car park designers’ handbook

Advantages . Can be used in layouts down to 24.000 m in length. . All turns are in the same direction with no single turn greater than 908. . Simple recirculation and recirculation capability. Disadvantages The outflow route passes all of the stalls. . The use of narrow (3.300 m) width ramps reduces dynamic efficiency and they are not popular with motorists. . Potential conflict between drivers when they arrive, side by side, from different levels and turn in the same direction. . Pedestrian access requirements between split levels will reduce static capacity and, on the smaller layouts, may be difficult to incorporate (see SLD 1). .

Comments The circulation efficiency is high. All of the stalls on the inflow route can be passed with just four right-angled turns. Unfortunately, it is also the outflow route and at busy times traffic congestion can occur as the inflow and outflow traffic combines. . As shown, only 12 stall spaces per deck are needed to complete the circulation route. This is highly efficient and can only be bettered by an SD 5 layout. . When constructed in pairs, between three stall widths, side-by-side ramps are below 3.300 m in width between faces of structure. This is less than the minimum entry width recommended for crossramps (see Section 3.6.10). . Mainly suitable for private parking (staff and hotel type), where the available site area is small and the need to squeeze in as many spaces as possible is great. . Unless drivers use the full width of the traffic aisles to effect their turn into the narrow ramps they risk scraping their vehicles on the sidewalls (see Fig. 3.15 and Section 3.6.12). . Although many car parks in the 1960s and 1970s were constructed with these narrow ramp widths, they are unpopular, especially with drivers of larger-type vehicles, and cannot be recommended for use by the general public. . In small facilities they could be justified on the grounds of improving static capacity, but in such cases it is important not to obstruct lateral vision as drivers approach the ramp ends. .

Static efficiency Increasing the deck length to 28 stalls, for comparison purposes, produces an area per car space of 21.060 m2 . This can be deemed, Good. . As the length reduces so the area requirements increase. At its shortest length (24.000 m), the area per car space becomes 26.750 m2 . .

Other layouts An SLD 6 or a VCM 3 is to be preferred provided that the increased aisle width can be tolerated but there is no alternative layout incorporating a one-way traffic flow that can be constructed under an overall length of 36.000 m (15 stall widths).

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Circulation layouts

49

SLD 4 Combined one-way-flows, three bins or more wide

SLD 4 Combined one-way-flows, three bins or more wide

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Car park designers’ handbook

Advantages . Simple circulation and recirculation capability. . Good static efficiency using only 16 stall spaces to complete the circulation route. Disadvantages 66% of the stalls have to be passed on the outflow route (no rapid exit route). . Both flow routes combine on the central aisle, a condition that could result in traffic congestion at busy times. . At one end, when turning onto the central aisle, drivers confront each other. . A minimum of seven stalls will be lost at each of the two split levels if a pedestrian ramp access is required between adjacent bins. .

Comments Stall searching on the inflow circuit passes 66% of the stalls. To pass all of the spaces on each storey and reach the next deck above involves driving once through aisle 1, three times through aisle 2 and twice through aisle 3. . The circulation efficiency of this search pattern is quite poor. . The alternative of climbing all the way up on the inflow circuit and returning back down on the outflow circuit is more efficient but still involves driving through the central aisle twice per storey. It is not a search pattern that normally appeals to motorists. . The introduction of variable message signs, showing the availability of stalls on the outflow aisle, will reduce the search pattern to a simple rectangle with four turns to the right for each storey. . At the entry to the central aisle, where the inflow and outflow routes confront each other, the situation can be improved by introducing a peninsula, shaped to prevent motorists from driving straight across to the other ramp. .

Static efficiency A deck length of 28 stall widths produces an area per car space of 20.700 m2 . This can be deemed, Good.

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Other layouts . An SD 5 or an FSD 3 or 4 layout that is flat across the decks for pedestrians at each end has similar static efficiencies, provided that there is no need for internally located cross-deck pedestrian access. . A three-bin VCM 1 eliminates most of the split-level condition and the need for pedestrian ramps, thereby offsetting the greater number of stall spaces needed for circulation purposes. The flat deck areas are easier to supervise and more user friendly.

Circulation layouts

51

SLD 5 Combined one- and two-way-flows, three bins or more wide

SLD 5 Combined one- and two-way-flows, three bins or more wide

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Car park designers’ handbook

Advantages . Outflow and inflow routes circulate in the same direction. . Simple circulation and recirculation capability. Disadvantages 66% of stalls are passed on the outflow route. . The central aisle requires widening to accommodate two-way flow traffic. . Seven stalls will be lost at each split level if pedestrian ramp access between split levels is required. .

Comments Stall searching on the inflow circuit passes 66% of the stalls. To pass all of the spaces on each storey and reach the next deck above involves driving twice through aisle 1. . This is a superior circulation pattern to the SLD 4 layout although aisle 2, with two-way flow, is wider. . The alternative of climbing all the way up on the inflow circuit and returning back down on the outflow circuit is no more efficient since it still involves driving through the central aisle twice per storey. It is not a search pattern that normally appeals to motorists. . In similar fashion to the SLD 4 layout, circulation efficiency will be enhanced by the introduction of variable message signs. . The two-way traffic flow eliminates confrontation between drivers arriving on the central aisle and also reduces the possibility of traffic congestion. . Pedestrian access between the split levels is a problem and if required will reduce static capacity by 14 stalls per storey height. .

Static efficiency A deck length of 28 stall widths produces an area per car space of 20.700 m2 . This can be deemed, Good.

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Other layouts . An SD 5 or an FSD 2 or 3 layout embodying flat access at each end for pedestrians has similar static efficiencies and could eliminate the need for a pedestrian ramp. . Although a three-bin VCM 1 would eliminate the need for pedestrian ramps, fitting it onto a sloping site may cause problems of access and egress.

Circulation layouts

53

SLD 6 Two-way-flow with ‘combined’ ramps

SLD 6 Two-way-flow with ‘combined’ ramps

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Car park designers’ handbook

Advantages . Can be used in layouts down to 24.000 m in length (10 stall widths). . All stalls are located directly off the main inflow route. Disadvantages All stalls are located directly off the outflow route. . Two-way traffic-flow layouts are less efficient, statically and dynamically, when compared with one-way-flow layouts. . Recirculation is not a natural feature of two-way-flow layouts. . If pedestrian access is required between split levels, it will reduce static capacity. .

Comments This is a two-way-flow variation on an SLD 3 layout but without the potential driver conflict. The same number of stall spaces (12) is used to complete the circulation route. . It is more suitable for Cat. 3 or 4 uses, especially ‘tidal’, where the full width of the two-way-flow ramp can be used for one-way-flow traffic (a.m. and p.m.) and light two-way-flow traffic during the day. . For Cat. 4-type layouts, or where very light usage is anticipated, the recommended minimum width of 7.000 m can be reduced, provided that the client agrees with the reduction in standards. Consideration, however, should be given to possible future changes in the layout’s parking category. . It is desirable to eliminate obstructions to lateral vision at the top and bottom of the ramps if maximum dynamic efficiency is to be achieved. . In Cat. 4 layouts, especially where the traffic flows are mainly tidal, combined ramps are superior in dynamic efficiency when compared with scissors-type (SLD 3) ramp layouts. . Suitable for all parking categories up to, about, 300 spaces and somewhat larger car parks only with caution. The lack of a rapid outflow route and the two-way-flow preclude this layout from serious consideration for large-capacity Cats 1 and 2 car parks. .

Static efficiency Increasing the deck length to 28 stalls for comparison purposes produces an area per car space of 21.060 m2 . This can be deemed, Good. . As the length reduces so the area requirements increase. At its shortest length (24.000 m), the area per vehicle space becomes 26.750 m2 . .

Other layouts A VCM 3 layout is superior in dynamic efficiency and user-friendly features. . Above a length of 43.200 m, an SD 1 layout can also be considered. .

Circulation layouts

55

SLD 7 One-way-flow with an included contra-flow rapid exit route

SLD 7 One-way-flow with an included contra-flow rapid exit route

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Car park designers’ handbook

Advantages . All stalls are passed on the main inflow route. . Rapid outflow route. . Good recirculation capability. Disadvantages Right and left turns are required with some small reduction in dynamic efficiency when compared with one-way-flow layouts. . Seven stalls per deck will be lost if pedestrian ramp access is required between the split levels. . Confrontation between drivers can occur at the entrance to the internal outflow ramp. .

Comments This is, in effect, a minimum length SLD 6 layout with a one-wayflow split-level extension. . The inflow circuit passes all of the stalls with four right-angled turns per storey, but only the rapid contra-flow circuit has a combined traffic flow. This provides it with an improved dynamic and static efficiency when compared with a similar length SD 6 layout. . A penalty, however, is that an extra two stalls per storey are required to complete the circulation route and there will also be a driver conflict point where left and right turns occur at the entry into the rapid exit ramp. . The one-way-flow section can be constructed 2.000 m narrower than a two-way-flow deck, with a consequent reduction in construction costs. . It is not a layout that has been used often, but could help if the designer was presented with a restricted site width and the main entry/exit was located at the end of the access road. . ‘Give way’ signs, where traffic joins the rapid outflow route, reduce the problem of driver confrontation but cannot solve the problem altogether. . This layout is suited to all parking categories up to a maximum of, say, 400 spaces. Larger car parks should be of the Cat. 3 or 4 types, where intensive flow rates occur only in one direction at any particular time. .

Static efficiency A deck length of 28 stall widths produces an area per car space of 22.000 m2 . This can be deemed, Good. . At its shortest length it reverts to an SLD 6 layout. .

Other layouts A VCM 4 layout has a similar circulation pattern but without the split level, the central vehicle ramp and the need for a ‘dedicated’ pedestrian ramp. . Provided that the location of the main entry/exit is acceptable, above a length of 36.000 m an SLD 2 or a VCM 1 or 2 layout could be used to better effect. .

Circulation layouts

57

Fig. 7.3 An SD5 layout

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Car park designers’ handbook

7.6 Sloping parking decks (SDs)

Sloping parking decks (SDs) (see Fig. 7.3) have parking aisles that slope along their length, the cross-ramps between adjacent bins can be laid flat and become access-ways for both vehicles and pedestrians. The parking gradient must not exceed 5% (1 in 20). Vehicles can be parked on steeper sideways slopes but the requirements of BS 8300:8.2.2, for pedestrians must be observed in the UK. It should also be appreciated that a limiting criterion, especially for public car parks, is not the effect that sideways slopes have on parked cars, but the effect of gravity on the opening and closing of the doors. There are, however, drawbacks that render this type of layout less attractive than a split-level car park in other respects. They are: .

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Rapid inflow and outflow routes that enable motorists to bypass full or congested levels are not a practical proposition. Pedestrian access between adjacent decks, other than at the accessways, is not a practical proposition. Flat parking areas for disabled drivers must be provided that could extend the minimum length of the building.

Sloping parking decks are a popular format in the south and west of the USA, where they are used extensively for staff parking, invariably linked to an adjacent office block. Some examples of the SD 1-type layout occur in the UK, but very few compared with split-level layouts. It is, however, worthy of note that both SD 3 and WPD1 circulation patterns are the same. These layouts can be statically efficient and capable of floor areas per car space of 21 m2 , or even less in large-capacity facilities. An SD 7 layout has the best static efficiency of any car park type with two or more bins.

Circulation layouts

59

SD 1 Single helix with two-way-flow

SD 1 Single helix with two-way-flow

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Car park designers’ handbook

Advantages . All stalls are passed on the main inflow route. . Only 12 stall spaces per deck are required to complete the circulation route. . Flat access for pedestrians, between adjacent bins, at each end. . The sloping decks provide an unmistakable indication of the direction of traffic flow: inflow is upwards and outflow is downwards (reversed in underground facilities). . Storey heights can be varied almost infinitely by means of the deck length and slope. Disadvantages No rapid outflow route. . Two-way traffic flows are less efficient, both statically and dynamically, than one-way-flow layouts. . The maximum sideways parking slope of 5% results in a minimum length overall, of 43.200 m (18 stall widths) for a 2.900 m storey height. . There is no natural recirculation capability. Drivers must turn through 1808 on the aisles, or use a ‘turning head’ that is usually located at the end of the aisle furthest from the entrance. . Pedestrian access between adjacent bins can only be made at each end. .

Comments At busy times, the two-way-flow circulation route, with vehicles entering and leaving stalls from both sides of the aisle, can result in a traffic congested situation developing quite rapidly, especially at the lower levels of a large-capacity building. . Although vehicles can safely park on much steeper sideways slopes than 5%, it is the effect of opening car doors against gravity that must be considered for weaker members of the parking public. . BS 8300 stipulates that when the ‘going’ is in excess of 10.000 m, the maximum slope for pedestrians must not exceed 5%. . This is a sloping deck version of an SLD 6 layout, but has flat access for pedestrians between adjacent bins each end. . Suitable for all category facilities up to 300 spaces capacity approximately and somewhat larger Cats 3 and 4 car parks with caution. The lack of a rapid outflow route and the two-way-flow precludes this layout from serious consideration for large-capacity public facilities. .

Static efficiency For comparison purposes, a deck length of 28 stall widths produces an area per car space of 22.300 m2 . This can be deemed, Good. . At its shortest length (18 stall widths) the area per car space increases to 23.900 m2 . .

Other layouts An SLD 6 has a similar static efficiency but lacks the pedestrian access between adjacent bins at each end. . A VCM 3 layout has a superior dynamic efficiency and user-friendly features. . A VCM 4 layout is similar in dynamic efficiency and static capacity, but is superior in user-friendly features. .

Circulation layouts

61

SD 2 Single helix with one-way-flow and a rapid outflow route

SD 2 Single helix with one-way-flow and a rapid outflow route

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Car park designers’ handbook

Advantages . Twelve stalls per storey height are used to complete the circulation route. . Flat access for pedestrians across the deck at each end. . Rapid outflow route. . Full recirculation capability. Disadvantages Pedestrian access is limited to the ends of the parking decks. . Including the ramp, a minimum site length of 50.000 m, approximately, will be required. .

Comments The smaller dimensions required for one-way-flow parking ramps enables savings of 161 m2 per storey to be made when compared with the featured SD 1 layout. The rapid outflow ramp has an area of 184 m2 per storey height and when the layout is extended to a length of 52.8 m, the parking area savings will balance the increase in ramp area. It also has the added benefit of a separated rapid outflow route and an ability to re-circulate throughout all of the parking decks. . Although shown with a three-slope outflow circuit, any of the featured HER series ramps can be used. . ER series ramps can also be used although they will be more expensive to construct and will take up a larger site area. . Recommended for all parking categories up to about 600 spaces, above which the lack of a rapid inflow route restricts its efficient use to Cat. 3 and 4 layouts. The upper limit is dependent upon the maximum traffic-flow rate anticipated on the lowest level of the outflow ramp. .

Static efficiency A deck length of 28.5 stall widths (68.400 m) produces an area per car space of 22.070 m2 . This can be deemed, Good.

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Other layouts . Although dynamically superior to an SD 1 layout for all car park capacities, it is statically inferior in its utilisation of the site area. An SD 1 layout over the site length will contain more stalls. . Constructing the ramp as the outflow route for a VCM layout, with parking on each side, can offset the static inferiority. But then why not ‘go all of the way’ and construct an SLD- or VCM-type layout?

Circulation layouts

63

SD 3 Double helix, end connected with one-way-flow on the central access-way

SD 3 Double helix, end connected with one-way-flow on the central access-way

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Car park designers’ handbook

Advantages . Flat access-ways between adjacent bins for vehicles and pedestrians, in the middle and at each end. . Simple circulation and recirculation capability. The inflow route slopes upwards and the outflow route slopes downwards. . Storey heights can be varied almost infinitely by means of the deck slope and length. Disadvantages 50% of the stalls are located on the outflow route. . If intended for large-capacity Cat. 1 or 2 use, the possibility of confrontation between inflow and outflow traffic entering the central access-way will require careful consideration. . Separating the traffic by widening the central access-way reduces the possibility of confrontation on entry but can create vehicle conflict points at the exit. . No rapid inflow or outflow route capability. . Requires a minimum building length of 72.000 m (30 stall widths). .

Comments This is a popular layout in parts of the USA where it is often linked to an adjacent office block and used for staff parking. In such buildings the traffic flows are mainly ‘tidal’ and the use of the central accessway for both inflow and outflow traffic is not an important factor. . When proposed for Cat. 1 or 2 parking the circulation pattern is not good. Searching all of the spaces on the way up involves driving twice through the inflow route on each parking level in order to recommence the search on the floor above. . At busy times in Cats 1 and 2 layouts, the doubling of the driving distance on the inflow route will extend parking times and become a cause of traffic congestion. . The introduction of a variable message sign system on each deck level will eliminate the need for motorists to drive unnecessarily through the outflow route and also remove the need to double the driving distance on the inflow route. . Slopes for pedestrians and sideways parking vehicles should not exceed 5%. . Dependent upon parking capacity and category of use, 12 to 16 stall spaces per deck are used to complete the circulation route. . The layout has the inflow and outflow traffic combining on the central access-way and is best suited where the main vehicle entry and exit points are located on opposite sides of the central access-way. .

Static efficiency The minimum deck length of 31 stall widths produces an area per car space of 21.100 m2 . This can be deemed, Good.

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Other layouts . VCM 1 and 2, incorporating rapid outflow routes and good crossdeck pedestrian access are more acceptable layouts for Cats 1 and 2 use. . SLD 2 is also worth considering, provided that pedestrian access between adjacent bins is not a necessary design feature.

Circulation layouts

65

SD 4 Double helix, end connected with two-way-flow on the central access-way

SD 4 Double helix, end connected with two-way-flow on the central access-way

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Car park designers’ handbook

Advantages . Flat access-ways between adjacent bins for vehicles and pedestrians, in the middle and at each end. . Simple circulation and recirculation capability. . Storey heights can be varied almost infinitely by means of the sloping deck. Disadvantages Half of the stalls are located on the outflow route. . No rapid inflow or outflow route capability. . Requires a minimum building length of 76.800 m (32 stall widths). .

Comments A variation on the SD 2 layout, the traffic circulation incorporates 908 turns to the left with a two-way traffic flow on the central aisle. With this layout, the preferred main entry/exit location will be on one side of the central aisle. . The circulation route is somewhat simpler than SD 3. Figure-of-eight turns and confrontation are avoided but in other respects it remains the same, with only 50% of the stalls located on the inflow route. . The introduction of a variable message sign system on each deck level towards the end of the inflow ramp, just before the left turn onto the central access-way, will eliminate the need for motorists to, fruitlessly, drive around the outflow route and render the search for parking space much more efficient. . Sixteen stall spaces per deck are used to complete the circulation route. In suitable conditions this can be reduced to 14 by making the central access-way three stalls wide. .

Static efficiency The minimum deck length of 32 stall widths produces an area per car space of 21.400 m2 . This can be deemed, Good.

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Other layouts . VCM 1 and 2, with rapid inflow and outflow routes and good crossdeck pedestrian access are more acceptable for Cats 1 and 2 use. . SLD 2 is also worthy of consideration, provided that pedestrian access between adjacent bins is not a necessary design feature. . SD 3, 4 and 5 layouts have similar characteristics. They are all capable of being used for Cat. 4 purposes with flow reversal where both routes are used for inbound traffic in the mornings and outbound traffic in the afternoons. . SD 3 and 4 layouts incorporate superior recirculation capabilities and SD 5 has a superior static efficiency.

Circulation layouts

67

SD 5 Interlocking double helix, with one-way-flows

SD 5 Interlocking double helix, with one-way-flows

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Car park designers’ handbook

Advantages . Only eight stalls per storey height are used to complete the circulation route. . Flat access for pedestrians across the deck, at each end. Disadvantages No rapid inflow or outflow route capability. . No re-circulation capability within the car park. . Pedestrian access is limited to the ends of the parking decks. . Cannot be constructed less than 70.000 m in length. .

Comments Each complete circuit of 3608 raises two storeys, with the outflow route ‘sandwiched’ between the decks of the inflow route. . If motorists are not to drive against the traffic flow, then regardless of where they have parked on the inflow circuit, upon leaving they must carry on up to the top deck in order to join the outflow circuit and then drive back down. . It is, essentially, an SD 3 layout but without the central access-way on the intermediate deck levels and the ability to change from one flow route to another. . The main merit in adopting this layout is its good static efficiency that saves six stalls per deck when compared with an SD 3 layout and eight stalls per deck when compared with an SD 4 layout. . A pedestrian walkway between the adjacent decks can be introduced in the middle of the layout that uses two stalls. . Variable message sign systems are not appropriate for use with this layout. . It cannot be recommended for Cat. 1, 2 or 3 use but, if used as a Cat. 4 car park with ‘tidal’ flow, the outflow route can be reversed in the mornings and the inflow route in the afternoons to make twin entry and exit locations. If used in this manner, it will be dynamically and statically more efficient than an SD 1, 2, 3 or 4 layout. .

Static efficiency The minimum deck length of 30 stall widths produces an area per car space of 20.060 m2 . This can be deemed Very Good.

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Other layouts It cannot be matched by any other two-bin layout for static efficiency. However, for Cats 1, 2 and 3 use, SD 3 and 4 layouts are dynamically superior, more flexible and user friendly. . If used for Cat. 4 purposes with flow reversal, it will be statically superior to all other types of car park. .

Circulation layouts

69

SD 6 Combined helix, side connected with one- and two-way-flows

SD 6 Combined helix, side connected with one- and two-way-flows

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Car park designers’ handbook

Advantages . Simple circulation and recirculation capability. . Flat access for pedestrians between adjacent bins at each end. . The sloping decks provide an unmistakable indication of the direction of traffic flow; inflow is up and outflow is down. . Storey heights can be varied almost infinitely by means of the deck length and slope. Disadvantages No rapid outflow route. . Two-way traffic flows are less efficient, both statically and dynamically, than one-way-flow layouts. . Pedestrian access between adjacent bins is restricted to each end. . Access between adjacent decks occurs only at the ends of the aisles. .

Comments The inflow circulation route only passes 66% of the stalls, and the outflow route also passes 66% of the stalls. . This is a three-bin width version of an SD 1 layout. The central aisle needs to be widened to accept a two-way traffic flow and all turns are made in the same direction. . The mixing of traffic on the central aisle and the extended outflow circuit renders this layout unsuitable for large capacity Cats 1 and 2 uses. . Two-way traffic flows are dynamically less efficient than one-wayflow layouts. . Searching for stalls on each level involves driving twice through the external aisle on the inflow route: it is inefficient and can lead to unnecessary traffic congestion. . The introduction of a variable message sign system on each deck level, positioned just before the left turn onto the central accessway, will eliminate the need for motorists to, fruitlessly, drive around the outflow route and render the search for parking space more efficient. .

Static efficiency A deck length of 16 stall widths contains 80 stalls and produces an area per car space of 22.900 m2 . This can be deemed, Average.

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Other layouts . Good static efficiency is a strong feature of this layout, but, in most other respects, an SLD 2, VCM 1 or 2 layout, three bins wide, with superior dynamic efficiency and more user-friendly layout, could be used to advantage for all categories of use.

Circulation layouts

71

SD 7 and 8 Double helix, side connected, with one-way-flows

SD 7 Double helix, side connected, with one-way-flows

SD 8 Double helix, side connected, with one-way-flows (version of SD 7)

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Car park designers’ handbook

Advantages . Simple recirculation capability. . Flat access for pedestrians across the deck at each end. Disadvantages 50% of the stalls are located on the outflow route. . No rapid inflow or outflow route capability. . Pedestrian access is limited to the ends of the parking decks. .

Comments These are two variations on the same theme. SD 7 is the more popular layout with two of the four sloping decks side by side, all of the turns in the same direction, a superior circulation flow and no vehicle confrontation. SD 8 has been shown merely to emphasise this superiority. . The use of 24 stall spaces per deck to complete the circulation route is quite high when compared with an SD 1 layout that uses only 12. The orientation of the traffic aisles, however, can result in them being shorter, thereby reducing the travel distance for pedestrians to the flat access-ways at either end of the traffic aisles. The multiplicity of shorter aisles could be of benefit to pedestrians in a Cat. 1 or 2 car park. . Searching for stalls on each level involves driving twice through each of the external aisles before climbing to an upper level. This is not an efficient search pattern and can lead to early traffic congestion at busy times. . An alternative search pattern is to drive directly up to the top parking level, then transfer to the outflow route and continue searching on the way back down. This is more efficient dynamically, but not one that the parking public is likely to accept readily. . The introduction of a variable message sign system on each deck level will eliminate the need for motorists to needlessly drive around the outflow route, thereby improving the circulation efficiency. . SD 7 occurs occasionally, but SD 8 is not known to occur in the UK. .

Static efficiency A minimum deck length of 16 stall widths contains 88 stalls and produces an area per car space of 23.040 m2 . This can be deemed, Average.

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Other layouts Four-bin width versions of SLD 2, VCM 1 and VCM 2 provide superior layouts on suitably sized sites, especially if considered for Cat. 1 or 2 purposes. . If there is room on the site to accommodate HER- or ER-type ramps then flat parking decks will also provide a superior option for largecapacity car parks. .

Circulation layouts

73

Fig. 7.4 An FSD 5 layout

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Car park designers’ handbook

7.7 Combined flat and sloping deck (FSD) layouts

Circulation layouts

The practical advantage of these layouts (see, for example, Fig. 7.4) over those featured in the SD series is that the parking decks can be laid horizontally on three sides of the building in a two-bin configuration and on all four sides of buildings which are three or more bins wide. The flat elevation feature has possible benefits of an architectural nature in some circumstances. The flat deck elements can incorporate stalls for disabled drivers and carers. The length of the deck, raising a complete storey height, renders these layouts suitable only for buildings of a length greater than about 72.000 m (30 stall widths). The physical barrier to pedestrians progressing across the decks limits these layouts to sites where the main point of pedestrian access occurs at the ends of a traffic aisle. Rapid inflow or outflow routes are not a practical proposition. End-connected flow routes require a minimum building length of 128.800 m to operate successfully. They are not considered to be a viable construction form for UK use and for this reason they have not been featured. They are a popular format in the USA, where they are used mainly for ‘main terminal’ use and staff-type parking in multiple bin layouts, linked to large office buildings. They are a rare occurrence in the UK.

75

FSD 1 Single helix with two-way-flow

FSD 1 Single helix with two-way-flow

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Car park designers’ handbook

Advantages . Horizontal elevations on three sides. . All stalls are located directly off the main inflow route. . Flat pedestrian access between adjacent bins at each end. . Storey heights can be varied almost infinitely by means of the sloping deck length and slope. Disadvantages All stalls are located directly off the main outflow route (no rapid exit route). . Access between decks is restricted to the ends of the aisles. . There is no natural recirculation capability. Drivers must turn through 1808 on the aisles, or use a ‘turning head’ that is normally located at the end of the aisle furthest from the entrance. . A minimum building length of 72.000 m (30 stall widths) is required to incorporate a 5% parking slope. . Introducing a 5% pedestrian slope on the end access-ways can reduce the overall building length by 20.000 m, but in so doing two of the three flat elevations will be eliminated. . Two-way traffic flows are less efficient both statically and dynamically, when compared with one-way-flow layouts. .

Comments The circulation pattern is the same as any of the other two-bin layouts with two-way traffic flows. The main difference with this layout is in the storey height sloping parking deck on one side, resulting in a minimum building length longer than most others. . Locating the main stair/lift tower in the middle of one of the flank walls is to be preferred to reduce walking distances, but an access ramp between the bins is awkward to construct on a sloping deck and will lose several parking spaces. . The most effective location for the main pedestrian stair/lift tower will to be at either of the two ends, although this will entail pedestrians walking up to 70 m on a sloping deck to and from their vehicles. . The use of 12 stall spaces (or 16 if wider access-ways are used) to complete the circulation route renders it similar in operation to an SLD 6 or SD 1 layout. . The two-way traffic flow and lack of a separated rapid exit route renders this layout unsuitable for large-capacity Cats 1 and 2 use. .

Static efficiency A minimum deck length contains 108 stalls and produces an area per car space of 22.100 m2 . This can be deemed, Good.

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Other layouts . An SLD 6 and an SD 1 are similar in operation and can be constructed to a shorter overall length. . VCM 3 also has a similar circulation pattern, but the flat deck areas provide improved pedestrian access across the decks.

Circulation layouts

77

FSD 2 Single helix with one-way-flow and a rapid outflow route

FSD 2 Single helix with one-way-flow and a rapid outflow route

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Car park designers’ handbook

Advantages . Ten stalls are used to complete the circulation circuit. . Good recirculation capability. . Flat access between adjacent bins for pedestrians at each end. . Rapid outflow route. Disadvantages A pedestrian access ramp between adjacent decks is not a practical proposition. . Including the ramp, a minimum site length of 87.000 m, approximately, will be required. .

Comments The smaller dimensions required for one-way-flow parking ramps enables a saving of 224 m2 per storey to be made when compared with the featured FSD 1 layout. . The rapid outflow ramp has an area of 184.000 m2 per storey, approximately. . At its minimum length of 30 stall widths savings of 40.000 m2 per storey can be achieved with all of the benefits of a separated rapid outflow route and an ability to recirculate throughout all of the decks. . Although shown with a three-slope outflow circuit, any of the featured HER series can be used. . ER series ramps can also be used although they will be more expensive to construct and will take up a larger site area. . Recommended for all parking categories up to about 600 spaces, where the lack of a rapid inflow route restricts its use for Cats 1 and 2 layouts. . For Cats. 3 and 4, the limit will be dependent upon the maximum traffic flow rate anticipated on the lowest level of the outflow ramp. .

Static efficiency A minimum deck length contains 106 stalls and produces an area per car space of 22.220 m2 . This can be deemed, Good.

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Other layouts . Although dynamically superior to an FSD 1 layout for all parking categories, it is statically inferior in its utilisation of the site area. An FSD 1 layout over the length, including the ramps, will contain more cars. . Constructing the ramp as the outflow route for a VCM layout with parking on each side can offset the static inferiority, but why not go all of the way and construct a complete VCM-type layout?

Circulation layouts

79

FSD 3 Combined helix, side connected with one- and two-way-flows

FSD 3 Combined helix, side connected with one- and two-way-flows

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Car park designers’ handbook

Advantages . Horizontal elevations to all four sides. . One-way-flow circulation with all turns in the same direction and with no single turn greater than 908. . Simple recirculation capability. . Flat access between adjacent bins for pedestrians at each end. Disadvantages 66% of the stalls are located on both the inflow and outflow route. . A minimum building length of 72.000 m is required (30 stall widths). . Two-way traffic flow on the central aisle. .

Comments Searching for stalls on each level involves driving twice through the external aisle on the inflow circuit before climbing to an upper level. This is not an efficient search pattern and can lead to early traffic congestion at busy times. . The alternative is to drive directly up to the top parking level, then transfer to the outflow route and continue searching on the way back down. This is, dynamically, more efficient but not one that the parking public is likely to accept readily. . The introduction of a variable message sign system on each deck level, positioned just before the left turn onto the central aisle, will eliminate the need for motorists to, fruitlessly, drive around the outflow route and render the search for parking space much more efficient. . Locating the main pedestrian stair/lift tower in the middle of one of the flank walls is to be preferred, but constructing two pedestrian access ramps between the bins will lose some 14 stalls per floor, be awkward to construct on a sloping deck and be costly. . The most efficient location for the main pedestrian stair/lift tower will to be at either of the two ends, although this will entail pedestrians walking up to 70 m on a sloping deck to and from their vehicles. . The use of 16 stall spaces per deck to complete the circulation route renders it similar in static efficiency to an SLD 4 and a FSD 3 layout. . The lack of a rapid inflow or outflow route renders it unsuitable for large capacity Cat. 1 or 2 purposes. . The main advantage of adopting this layout is the flat elevations to all four sides. .

Static efficiency A minimum deck length contains 152 stalls and produces an area per car space of 21.130 m2 . This can be deemed, Good.

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Other layouts . Apart from the four flat elevations, a VCM 1 layout, three bins wide, with its superior dynamic efficiency and user-friendly layout, could be used to advantage for all categories of use. . If pedestrian access between bins is not a requirement, an SLD 3 layout could also be considered.

Circulation layouts

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FSD 4 Combined helix, side connected with one-way-flow

FSD 4 Combined helix, side connected with one-way-flow

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Car park designers’ handbook

Advantages . Simple recirculation capability. . Flat access between adjacent bins for pedestrians at each end. . Although the two outside aisles have been shown sloping with a flat central aisle, it can be reversed, with the outside aisles laid flat and a sloping central aisle (not dissimilar to FSD 2). The traffic circulation remains the same. Disadvantages The central aisle is common to both the inflow and outflow routes. . ‘Opposing driver’ conflict is possible at the entry to the central aisle. . A minimum building length of 72.000 m is required (30 stall widths). .

Comments The reduced width of the one-way-flow central aisle renders this layout more economical to construct than an FSD 3 layout (about 2%). . Searching for stalls, storey by storey, is less efficient than an FSD 3 layout, involving the external aisle on the inflow route being driven through twice, the central aisle, three times (twice on an upper level and once on the level under) as well as the external aisle on the outflow route. This is double the driving distance required in an SLD 1 layout and will lead to premature traffic congestion at busy times. . The alternative is to drive directly up to the top parking level, then transfer to the outflow route and continue searching on the way back down. This is dynamically more efficient, but is not one that the parking public is likely to accept readily and still requires both traffic flows to merge on the central aisle. . The introduction of a variable message sign system, positioned at the far end of the central aisle will eliminate the need for motorists to, needlessly, drive around the outflow route. . It is almost essential that the main pedestrian stair/lift tower will have to be located at either of the two ends although this will entail some pedestrians walking more than 80 m on a sloping deck to and from their vehicles. . The use of 16 stall spaces per deck to complete the circulation route renders it similar in operation to an SLD 5 or FSD 3 layout. . The lack of a rapid inflow or outflow route renders it unsuitable for large-capacity Cat. 1 or 2 purposes. .

Static efficiency A minimum deck length contains 152 stalls and produces an area per car space of 21.130 m2 . This can be deemed, Good.

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Other layouts . Good static efficiency is a strong feature of this layout, but, in all other respects, a VCM 1 layout, three bins wide, with its superior dynamic efficiency and user-friendly layout, could be used to advantage for all categories of use. . If pedestrian access between bins is not a problem, an SLD 5 layout could also be considered.

Circulation layouts

83

FSD 5 Double helix, side connected with one-way-flow

FSD 5 Double helix, side connected with one-way-flow

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Car park designers’ handbook

Advantages . Horizontal elevations to all four sides. . Good recirculation capability. . All turns are made in the same direction. . Flat access between adjacent bins for pedestrians at each end. Disadvantages No rapid inflow or outflow route capability. . Twenty-four stall spaces per deck are used to complete the circulation route. . Pedestrian access ramps between adjacent decks are not a practical proposition. .

Comments Searching all of the spaces, storey by storey, involves driving three times on the external inflow aisle, twice on the internal inflow aisle, once on the internal outflow aisle and twice on the external outflow aisle. This produces low-circulation efficiency and can be a direct cause of traffic congestion at busy times. . Introducing a left turn at the bottom of the outflow circuit on each level can create a ‘short cut’, eliminating two of the ‘legs’, but this uses four stalls, reducing static efficiency. . The alternative is to drive directly up to the top parking level, then transfer to the outflow route and come back down again. This is more efficient, dynamically, but not one that the parking public is likely to accept readily. . The introduction of a variable message sign system on each deck level, positioned just before the left turn onto the central aisle, will eliminate the need for motorists to, fruitlessly, drive around the outflow route and renders the search for parking space more efficient. . Locating the main pedestrian stair/lift tower in the middle of one of the flank walls is to be preferred but, as a pedestrian access ramp between adjacent bins is not a practical proposition, it will entail those drivers who park in the far bin walking to the ends of the aisles, crossing on the access-ways and returning to the middle. This will not be popular with the parking public. . There are few examples in the UK, but versions do occur in the USA, some with 708-angled parking and used mainly for staff- and airporttype parking. . The lack of a rapid inflow or outflow route renders it unsuitable for Cat. 1 or 2 purposes. .

Static efficiency A minimum deck length contains 200 stalls and produces an area per car space of 20.960 m2 . This can be deemed, Good.

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Other layouts . Four-bin versions of SLD 3, or VCM 1 or 2 with their superior dynamic efficiency and user-friendly layouts, could be used to advantage for all categories of use. . If there is room on the site to accommodate external ramps, without a reduction in static capacity, then flat deck layouts could also provide a superior solution. . FSD 5 and 6 have similar characteristics.

Circulation layouts

85

FSD 6 and 7 Double helix, side connected with one-way traffic flows

FSD 6 Double helix, side connected with one-way-flows (version of FSD 5)

FSD 7 Double helix, side connected with one-way-flows (version of FSD 5)

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Car park designers’ handbook

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Circulation layouts

These are versions of the FSD 4 layout, obtained by sloping the decks in different ways. The circulation pattern is poor without the use of variable message sign systems and they embody no advantages or disadvantages. They are shown merely to indicate the circulation variations that can be obtained with multi-bin layouts.

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FSD 8 Single helix with one-way-flow and an internal ramp

FSD 8 Single helix with one-way-flow and an internal ramp

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Car park designers’ handbook

Advantages . Horizontal elevations on three sides. . Flat pedestrian access between adjacent bins at each end. . Storey heights can be varied almost infinitely by means of the sloping deck length and slope. Disadvantages Only 50% of the stalls are passed on the inflow route. . Access between decks is restricted to the ends of the aisles. . A minimum building length of 76.800 m (32 stall widths) is required to incorporate a 5% parking slope. . Introducing a 5% pedestrian slope on the access-ways can reduce the overall building length by 20.000 m, but in so doing two of the three flat elevations will be eliminated. .

Comments The circulation pattern is much the same as any of the other two-bin layouts with one-way traffic flows. The main difference with this layout is in the two half storey-height sloping decks on one side. . Locating the main pedestrian stair/lift tower in the middle of one of the flank walls is to be preferred. The central vehicle ramp is to be considered non-pedestrian and a dedicated pedestrian access ramp between the bins is awkward to construct on a sloping deck. It will also lose several parking spaces. . The most efficient location for the main pedestrian stair/lift tower will be at either of the two ends, although this will entail pedestrians walking up to 70 m on a sloping deck to and from their vehicles. . The use of 16 stalls per deck to complete the circulation route renders it similar in operation to an SD 4 layout. . The introduction of a variable message sign system on each deck level, towards the end of the inflow ramp just before the right turn onto the central ramp, will eliminate the need for motorists to, fruitlessly, drive around the outflow route and render the search for parking space much more efficient. .

Static efficiency The minimum deck length of 32 stall widths produces an area per car space of 21.400 m2 . This can be deemed, Good.

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Other layouts . VCM 1 and 2, with rapid inflow and outflow routes and good crossdeck pedestrian access, are more acceptable for Cats 1 and 2 use. . SLD 2 is also worthy of consideration provided that pedestrian access between adjacent bins is not a necessary design feature. . SD 3, 4 and 5 layouts have similar characteristics. They are all capable of being used for Cat. 4 purposes with flow reversal, where both routes are used for inbound traffic in the mornings and outbound traffic in the afternoons. . SD 3 and 4 layouts incorporate similar recirculation capabilities and SD 5 has a superior static efficiency.

Circulation layouts

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Fig. 7.5 A VCM 1 layout

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7.8 Combined flat and sloping deck layouts with internal cross-ramps (VCM and WPD)

Stacking one module upon another creates a continuous vertical circulation flow for a structured parking facility and joining two modules at their ramps (one the mirror image of the other), creates a complete car park circulation system where pedestrians can reach all parts of the deck without negotiating any slope in excess of 5% (VCM 1). The modules can be a minimum dimension of eight stall widths in length with a slightly twisted or a 5% sloping access-way, or they can be extended in length to ten stalls which renders them more suitable for precast concrete structures. Outside of the modules, the parking decks are laid flat, resulting in a significant improvement in crossdeck accessibility for pedestrians. The modules can be moved to other locations, as can be seen in VCM 2, although this is not such a popular layout as VCM 1. Modifying a module to accept two-way traffic flows creates a layout that can be constructed down to ten stall widths (24.000 m) in length, yet still retaining pedestrian access to any part of the deck (VCM 3). A VCM layout is more user friendly than other internally ramped systems and the 5% slopes provide access to any part of a parking deck, thereby eliminating the need for a separate dedicated pedestrian ramp. This reduces construction costs, enhances static efficiency and increases user friendliness. In large-capacity parking decks, rapid inflow routes can be introduced at any future time and at minimal cost; it is simply a matter of line painting. One-way-flow layouts can be constructed with a minimum dimension of eight stall widths while still retaining flat access for pedestrians along one long side (see the MD series on pp. 113–123). Warped parking deck (WPD) is a circulation system that provides the external appearance of a residential or office building, with all four sides appearing to have flat decks, without slopes or steps. This has some architectural advantages, but involves warping the parking decks that slope up to 9% in a cross-fall direction and 5% longitudinally. It cannot be constructed less than 74.400 m in length. Rapid flow routes are not a practical proposition and pedestrian access between adjacent decks is restricted to the aisle ends. It cannot be achieved without losing several stalls on each deck. It was a popular construction form some 30 years ago and examples of this type of building still occur.



VCM is a patented circulation system and must not be used without permission. For information regarding its use, contact Hill Cannon UK LLP, Royal Chambers, Station Parade, Harrogate HG 1EP, North Yorkshire. Telephone: 01423 562571.

Circulation layouts

91

VCM 1 One-way-flow with two one-way-flow ramps

VCM 1 One-way-flow with internal ramps

VCM 1 One-way-flow with two-way-flow ramps (version of 1)

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Car park designers’ handbook

Advantages . All turns are made in the same direction with no single turn greater than 908. . Pedestrians do not encounter slopes steeper than 5%. . A rapid inflow route can be incorporated at any time without structural alteration. It is simply a matter of line painting. . If access between adjacent bins is required, omitting two stalls can provide it, or the rapid inflow route can be used, thereby eliminating the need for a dedicated pedestrian ramp. . The inflow traffic route is separated from the rapid outflow route with exiting traffic passing only 24 stalls on each deck level. . Simple recirculation capability. Disadvantages Cannot be used in layouts less than 36.000 m (15 stall widths) in length.

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Comments Sixteen stall spaces per deck are required to complete the circulation route (14 if a combined ramp is used). . The separation of the two flow routes results in a more efficient circulation layout when compared with an SLD 1 layout, especially when used in Cats 1 and 2 layouts of a greater capacity than 400 stalls. . As drawn, the inflow circuit enables 80% of the stalls on each level to be searched efficiently, with just four right-angled turns. Many of the stalls on the outflow route can be seen and judgements made on whether to search that circuit. . Dynamic efficiency is good and similar to an SLD 3 layout, but it is more user-friendly. . The main pedestrian access tower can be located anywhere around the building, but is most suitable where it can be located away from the sloping deck elements. . Suitable for all parking categories and building sizes where the dynamic capacity of the rapid outflow route is not exceeded. . VCM 1A has the same plan form as VCM 1, but the elevations are horizontal on all four sides and the decks warp to a maximum of 7% at the ramp. .

Static efficiency As drawn, the number of stalls is 96 and the static efficiency, at 21.840 m2 per car space, can be deemed, Good.

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Other layouts . A VCM 2 layout could be considered where it is preferred to locate the flat deck element in the middle part of the deck. . A site with steep cross-falls could render an SLD 3 layout worthy of consideration.

Circulation layouts

93

VCM 2 One-way-flow with end ramps

VCM 2 One-way-flow with end ramps

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Car park designers’ handbook

Advantages . All turns are in the same direction with no single turn greater than 908. . The need for dedicated pedestrian ramps, between adjacent bins, is eliminated. . Pedestrians need not encounter slopes steeper than 5%. . The inflow traffic route is separated from the rapid outflow route with exiting traffic only passing 24 stalls on each deck level. . The traffic flows are separated and outflow route is rapid. . Simple recirculation capability. Disadvantages Cannot be used in layouts less than 36.000 m (15 stall widths) in length. . Some static efficiency will be lost if ‘dead ends’ are to be avoided on the lowest parking slopes. .

Comments Sixteen stall spaces per deck are required to complete the circulation route (14 if a combined ramp is used). . Circulation efficiency and characteristics are similar to a VCM 1 layout, except that there could be a reduction in static capacity at the very bottom of each flow route. . Dynamic efficiency is good and similar to an SLD 3 layout. . More suitable for layouts where the main pedestrian access tower is located at the side of the flat deck element in the middle part of the building. . Suitable for all parking categories and building sizes where the dynamic capacity of the rapid outflow route is not exceeded. .

Static efficiency As drawn, the number of stalls is 96 and the static efficiency, at 21.840 m2 per car space, can be deemed, Good.

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Other layouts . If dead ends at the lowest parking levels are omitted, the static capacity will be slightly less than a VCM 1 layout. . A site with steep cross-falls could render an SLD 2 layout worthy of consideration provided that the loss of spaces to pedestrian ramps can be tolerated.

Circulation layouts

95

VCM 3 Two-way-flow with a single end ramp

VCM 3 Two-way-flow with a single end ramp

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Car park designers’ handbook

Advantages . Only one VCM module is required, suitably modified for two-way flow. . All stalls are passed on the main inflow route. . Pedestrians do not encounter slopes steeper than 5%. . Can be constructed down to an aisle length of 24.000 m (10 stall widths) and still retain flat access for pedestrians progressing between adjacent bins. Disadvantages Reduced dynamic efficiency when compared with one-way-flow layouts.

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Comments At any time, a rapid outflow route can be introduced (as shown). It is simply a matter of line painting. . Twelve stall spaces per deck are required to complete the circulation route (16 if a rapid outflow route is incorporated). . The ramp and sloping deck element occurs over a length of 21.600 m, leaving the remainder of the parking deck to be constructed flat across the bins. . Without a rapid exit route it is only suitable for Cats 1 and 2 facilities up to about 400 spaces. If one was incorporated, up to about 700 spaces could be used without the fear of early traffic congestion. . It can be used in larger Cats 3 and 4 facilities, but if lacking a rapid outflow route it remains unsuitable for really large-capacity layouts. .

Static efficiency As drawn, the number of stalls is 96 and the static efficiency, at 22.210 m2 per car space, can be deemed, Good.

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Other layouts . An SLD 7 layout can be considered, especially if the site has a significant cross-fall, but will be inferior in user-friendly features and static capacity if pedestrian ramps between adjacent bins are required. . For aisle lengths greater than 43.200 m, an SD 1 layout can also be considered.

Circulation layouts

97

VCM 4 One- and two-way traffic flows with a single ramp

VCM 4 One- and two-way traffic flows with a single ramp

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Car park designers’ handbook

Advantages . Only one VCM module is required, modified for two-way flow. . A single circuit of each deck searches all of the stalls. . A rapid outflow route can be introduced when required. . One-way flow on the flat decks. . Good recirculation capability. . Pedestrians need not encounter slopes steeper than 5%. Disadvantages Some reduction in dynamic efficiency when compared with one-wayflow layouts. . Confrontation between opposing drivers can occur where they both turn onto the rapid outflow access-way. .

Comments At an aisle length of 24.000 m (10 stall widths) it reverts to a VCM 3 layout. . The ramp and sloping deck element occurs over a length of 21.600 m, leaving the remainder of the parking deck to be constructed flat across the bins. . Not suitable for Cats 1 and 2 purposes over, say, 300 spaces, it is equally unsuited for ‘tidal’ type traffic conditions where exiting traffic from opposing directions turns onto the internal access-way. . A ‘give-way’ box will help to improve the confrontation situation but cannot cure it altogether. . Larger car parks should be restricted to Cat. 3 use where problems caused by opposing drivers will be minimised. . The one-way-flow section saves 2.000 m on the width when compared with a VCM 3 layout, with a consequent improvement in static efficiency. . Fourteen stall spaces per deck are required to complete the circulation route. .

Static efficiency As drawn, the number of stalls is 100 and the static efficiency, at 21.080 m2 per car space can be deemed, Good.

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Other layouts . Above a length of 36.000 m a VCM 1 or VCM 2 layout could be used to advantage. . If access for pedestrians between adjacent bins is not a necessary design feature, an SLD 7 layout can also be considered, especially if the site has a significant cross-fall.

Circulation layouts

99

WPD 1 Warped parking decks with one-way-flow

WPD 1 Warped parking decks with one-way-flow

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Car park designers’ handbook

Advantages . The deck elevations are horizontal on all four sides. . Pedestrian access between adjacent bins occurs at each end of the traffic aisles. . Simple recirculation capability. Disadvantages The centrally located vehicle ramp in the middle of the layout is too steep for allowable pedestrian use. . Maximum allowable pedestrian slopes are also exceeded on the parking decks (see BS 8300:8.2). . A minimum length of 74.400 m (31 stall widths) is required when using 5% sideways parking slopes, but it is to be appreciated that the slope in the other direction can be in excess of 9%. . 50% of the stalls are located on the extended outflow route. . Fully laden shopping trolleys are difficult to control on parking decks incorporating falls in excess of 5%, especially when the aisle slopes are diagonal. .

Comments 16 stall spaces per deck are used to complete the circulation route (14 if a combined ramp were to be adopted). . The decks are horizontal at each end of the building and warp to a maximum at the central ramp locations. . A layout much used 30 to 40 years ago. Examples of this car park type have been constructed throughout the UK, some of which are still in operation. . Recent legislation has reduced the maximum slope allowed for pedestrians on ramps. .

Static efficiency As drawn, the number of stalls is 112 and the static efficiency, at 21.430 m2 per car space, can be deemed good.

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Other layouts The SD series share similar circulation features, especially SD 3, which incorporates an identical circulation layout and are more user friendly in having a flat central access-way for pedestrians. They cannot, however, be constructed with the deck sides horizontal. . A VCM 1 layout is more user friendly but without warping the decks it cannot be constructed with the building sides horizontal. However, the maximum deck slope in either direction does not exceed 5%. .

Circulation layouts

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Fig. 7.6 An FIR 1 layout

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Car park designers’ handbook

7.9 Flat decks with storey height internal ramps (flat with internal ramps – FIR)

Circulation layouts

In layouts three or more bins wide, internal cross-ramps can be introduced which climb through a complete storey height. In the UK this has been used, in the main, to create a horizontal elevation on all four sides of a multi-bin system, without resorting to sloping or stepped parking decks. Two basic types occur, those with ramps running across the bins and those where the ramps run parallel with the traffic aisles. The slope of the internal ramp is ‘recommended’ to be a maximum of 10%. Designers of existing buildings with cross-ramps have, in general, increased the ramp slopes slightly, with no known complaints from motorists. When used across the decks the dimension available for a ramp is usually 25.200 m. In the other direction, the length is unrestricted and can be ‘tailored’ to suit any storey height. The cross-ramp location results in an interruption to the free flow of traffic along the central bin resulting in a loss of stalls if dead ends are to be avoided. Dynamic and static efficiency is not a good feature of this layout type. The layouts featured show that drivers need to pass through some traffic aisles and access-ways more than once, in order to search all of the stalls on any particular level.

103

FIR 1 One-way-flow decks with combined two-way-flow ramps at right-angles to the aisles

FIR 1 One-way-flow with combined two-way ramps

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Car park designers’ handbook

Advantages . Horizontal elevations to all four sides. . All turns are in the same direction with no single turn greater than 908. . Simple recirculation capability. . Flat access for pedestrians between adjacent bins. . The outflow route is reasonably rapid. Disadvantages The internal ramps climb through a full storey height. Their length, between aisles, is 25.200 m; the maximum recommended slope is 10%. . The ramp crosses the central bin creating dead ends. . Thirty-two stall spaces per deck are required to complete the circulation route (36 spaces if all dead ends are to be avoided). . The static and dynamic efficiency is not good with many stalls having to be passed twice as each deck level is searched. .

Comments If the maximum allowable ramp slope of 10% is not exceeded, the storey height should not be greater than 2.560 m. For increased storey heights it will be necessary to extend the central bin dimension or create gaps between adjacent bins. . If all of the stalls are to be searched on each level and motorists drive up to the next parking level, they must drive more than twice the distance around the length of the perimeter aisles and access-ways. Circulation efficiency is low and can be a major cause of traffic congestion at busy times. . An alternative is to drive up to the top parking level on the inflow route, transfer over to the outflow route and continue searching on the way back down. Even so, on the inflow route one of the aisles has to be driven over twice. . The introduction of a variable message sign system can improve circulation efficiency, but the extended length access-ways, ramps and the need, still, to drive through some aisles more than once, do not make this layout as efficient as most of the others. . The high circulation requirement of up to 40 stall spaces per deck is a poor feature. . The minimum aisle length is 36.000 m (15 stalls), but at this length more than 30% of the stall spaces will be required to complete the circulation pattern. . The low circulation efficiency renders it unsuitable for any parking category where intensive activity is anticipated. .

Static efficiency As drawn, the number of stalls is 112 and the static efficiency, at 24.070 m2 per car space, can be deemed, Average.

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Other layouts . A VCM 1 layout, three bins wide, has superior static and dynamic efficiencies, without dead ends and is more user friendly. . If there were sufficient space on the site, any of the external ramp systems would also produce superior layouts.

Circulation layouts

105

FIR 2 One-way-flow decks with side-by-side (scissors type) ramps at right-angles to the aisles

FIR 2 One-way-flow with side-by-side ramps (scissors type)

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Car park designers’ handbook

Advantages . All turns are made in the same direction with no single turn greater than 908. . Horizontal elevations on all four sides. . Simple recirculation capability. . Flat access for pedestrians between adjacent bins. . The outflow route is reasonably rapid. Disadvantages The storey height ramps exceed the ‘recommended’ maximum slope. . The ramps cross an inner bin creating a short dead-end condition. . Thirty-two stall spaces per deck are required for ramps and accessways to complete the circulation route. . Thirty-six stalls are located directly off the combined inflow and outflow route. . Potential conflict between drivers when they arrive, side by side, at the same parking level and turn in the same direction. . The combined flow routes could result in traffic congestion at peak periods. .

Comments The circulation efficiency is a little better than an FIR 1 layout, but still requires two passes through the internal aisle to be driven in order to cover all of the spaces at each deck level. . Scissors-type ramps, at a width of 3.300 m, are not suitable for intensive traffic use. .

Static efficiency As drawn, the number of stalls is 112 and the static efficiency, at 23.230 m2 per car space, can be deemed, Average.

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Other layouts . A VCM 1 layout, three bins wide, can also be constructed with horizontal elevations and has superior static and dynamic efficiencies, without dead ends. . If there were sufficient space on the site, any of the external ramp systems would produce superior layouts.

Circulation layouts

107

FIR 3 One-way-flow decks with combined two-way-flow ramps parallel with the aisles

FIR 3 One-way-flow with two-way-flow ramps

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Car park designers’ handbook

Advantages . Horizontal elevations on all four sides. . Simple recirculation capability. . Flat access for pedestrians between adjacent bins. . The outflow route is reasonably rapid. . The ramps are located at right angles to the direction for a type FIR 1 layout. This enables a 10% sloping ramp to be introduced for any particular storey height. . Dead ends are eliminated. Disadvantages The high circulation requirement of 44 stall spaces per deck is a poor feature and can only really be justified by being incorporated within a much larger deck layout.

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Comments The layout is uncomplicated, the traffic pattern is simple to understand and is more efficient than that for an FIR 1 layout. . The higher circulation requirement should be weighed against the dynamic advantages when compared with an FIR 1 layout. .

Static efficiency Dependent upon the capacity of the deck within which it is incorporated, the overall static efficiency will vary. However, if constructed as a small independent layout, static efficiency will be in the order of 28 m2 per car space. This can only be described as Poor.

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Other layouts A VCM 1 layout, three bins wide, has superior static and dynamic qualities. . If there were sufficient space on the site, any of the HER and ER series could also produce superior layouts. .

Circulation layouts

109

FIR 4 One-way-flow decks with separated one-way-flow ramps

FIR 4 One-way-flow with edge ramps

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Car park designers’ handbook

Advantages . Flat decks. . Simple recirculation capability. . Flat access for pedestrians between adjacent bins. . The outflow route is reasonably rapid. . The ramps are located at right angles to the direction for a type FIR 1 layout. This enables a 10% sloping ramp to be introduced for any particular storey height. . Dead ends are eliminated. Disadvantages As drawn, 46 stall spaces per deck are required for ramps and accessways to complete the circulation route. . Potential conflict occurs between traffic exiting the ramps and filtering into the traffic on the aisles. .

Comments Although shown four bins wide, it can operate equally well with three bins. The ramps, however, will need to circulate in opposite directions. . The circulation efficiency is a little better than an FIR 1 layout, but still requires two passes to be driven through the internal aisle in order to cover all of the spaces at each deck level. .

Static efficiency If it forms part of a much larger deck layout it might be justified, but as a small ‘stand-alone’ layout the static efficiency can only be described as Poor.

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Other layouts A VCM 1 layout, three bins wide, has superior static and dynamic qualities. . If there were sufficient space on the site, any of the HER and ER series could also produce superior layouts. .

Circulation layouts

111

Fig. 7.7 An MD1 car park

Fig. 7.8 The entrance to an underground MD1 car park

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Car park designers’ handbook

7.10 Minimum dimension (MD) layouts

The smallest practical size for any parking layout is dictated by the recommended minimum turning circles for the SDV. It does not necessarily have to be over the full length of the building but at the ends, at least, in order to achieve a turning dimension. In continental Europe, ‘ring-spanner’ shaped layouts on several levels (MD 1, as shown in Figs. 7.7 and 7.8) occur under the main shopping streets of some towns, e.g. Rheims. They are ideal for very long and narrow sites both above and below ground and as they increase in length so their static efficiency improves, but there are no facilities of this type known to occur in the UK at the time of writing. A two-bin, SLD 3-type car park can be constructed down to a plan size of 31.200 m  24.000 m, dimensions that can only be matched by an SLD 6 and a VCM 3 layout. When, however, three or more bin widths can be incorporated in one direction, the other direction can be reduced to eight stall widths (19.200 m). Stalls 2.300 m wide reduce this dimension even further to 18.400 m and, if the parking need is great, the site is small and the client is amenable, such a reduction in parking standards may well be acceptable. A final reduction of the minimum dimension can be made, with caution. By reducing the number of stall widths to seven, a turning dimension of 16.800 m is produced. Although this is still greater than the notional turning circle for an SDV, the scratches down the ramp sides of existing car parks where it has been adopted, testify to the inadequacy of this dimension for public usage. However, if the client is amenable and the alternative is no car park at all, it could well be justified. A long MD 1-type layout can have a greater static efficiency than any other circulation design. (