Interim Guide On Identifying Prioritising and Treating Hazardous Locations On Roads in Malaysia - JKR 20708-0022-95

 

 

JKR 20708-0022-95

 

Interim Guide On   Identifing, Prioritising And  

Treating Hazardous

 

Locations On Roads

 

In Malaysia

m   m .0 7

m   m .0 5

Roads Branch Public Works Department Malaysia  Jalan Sultan Salahuddin 50582 Kuala Lumpur

 

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Interim Guide On Identifying, Priortising And Treating Hazardous Locations On Roads In Malaysia

FOREWORD Road accidents have now become a major concern in Malaysia. The latest accident figures from the Royal Malaysia Police show that the numbers have increased by 23% and 15% over the last two years alone, with 135,995 cases recorded for 1993. Malaysia's rapid economic growth may be  partly  par tly res respon ponsib sible le for for this this worry worrying ing trend trend as as the the count country ry is is curre currentl ntly y seein seeing g regis register tered ed vehi vehicle cless increase by over 7 % per year. In order to sustain high rates of economic growth, utilisation of the skills of our people is of paramount importance, and the nation can ill afford to waste such valuable resources in road accidents. Many would argue that to minimise human suffering in any way possible is sufficient justification in itself to devote greater efforts to reducing the road  accident casualty toll. Realising this, the Government set a reduction target in 1991 to reduce road accident fatalities by 30 per cent by the year 2000 with 1989 chosen as the base year. To achieve this target, all relevant Government Departments and Agencies need to contribute to this effort. The approach to be taken follows the 3 E's concept: Engineering, Education and Enforcement. Jabatan Kerja Raya (JKR)  being  bei ng the the main main Engine Engineeri ering ng arm arm of of the the Gover Governme nment nt can can play play a major major rol rolee in thi thiss respe respect. ct. In line with this, Institut Kerja Raya Malaysia (IKRAM) has undertaken a road safety research  progra  pro gramme mme in coll collabo aborat ration ion with with the the Tran Transpo sport rt Rese Researc arch h Labor Laborato atory ry (TRL (TRL)) of the Unite Unite King Kingdom dom.. As part of this initiative, IKRAM is now able to provide a reference guide for use by all practising road engineers in Malaysia. I am very pleased to be able to introduce this document, entitled  Interim Guide on Identifying, Prioritising and Treating Hazardous Locations on Roads in Malaysia and am grateful to the Overseas Development Administration, U.K. for their contribution to the funding of this project. This interim guide provides information specifically for Malaysia and sets out a standard  methodology for analysing accident data to help identify the most hazardous locations, select appropriate remedial measures, and evaluate this action. It is my hope that this Guide will be useful to all who are involved in the road safety field, helping them to channel limited resources in a more efficient manner, and thereby ensuring that our road network is as safe as it can possibly be made.

(T (Tan an Sri Dato’ Ir Wan Wan A Rahman Yaacob) Yaacob) Director General of Public Works Works Jabatan 1995 Kerja Raya Malaysia

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ACKNOWLEDGEMENTS This Guide has been prepared within the Road Safety Group of the Institut Kerja Raya Malaysia (IKRAM) in association with the Transport Research Laboratory (TRL), United  Kingdom. The author of the Guide is: Mr. Chris Baguley

-

TRL.

As its intended users are all road authority engineers in Malaysia, the Guide was reviewed at various stages of its production by the following representative Committee: Ir. Mohamed Shafii Mustafa IKRAM -Chairman Pn. Subiah Sulaiman IKRAM -Secretary Pn. Norliah Saidin Highway Planning Unit, Min.of Pub Works Ass. Prof. Radin U R Sohadi Universiti Pertanian Malaysia P/PPP Ru R uslan b. Khalid Polis Di Raja Malaysia PPP Ooi In Boo Polis Di Raja Malaysia Ir. Sabudin Mohd Salleh Dewan Bandaraya Kuala Lumpur   En. Sanusi b. Ismail Jabatan Kerja Raya Daerah, Hulu Langat and   representatives from Jabatan Perumahan & Kerajaan Tempatan; Majlis Keselamatan Jalan Raya; and Cawangan Jalan, Jabatan Kerja Raya. The author is indebted to the above committee members for their valuable contributions, and  to En. Othman Hussin of IKRAM for his assistance in preparing some of the material. Gratitude is also extended to Doncaster Metropolitan Borough Council and Berkshire County Council/Babtie Group for permission to reproduce parts of their Road Safety Plans, and to the Royal Society for the Prevention of Accidents (UK) for various extracts from their  Road Safety Engineering Manual. Finally, the author would also like to express his gratitude to the Director General of Public Works Malaysia for his permission to publish the Guide.

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CHAPTER I INTRODUCTION 1.1 PURPOSE AND SCOPE This Guide is intended for use by traffic engineers and road safety officers in the Public Works Department (JKR), Ministry of 

country.

Transport (MoT), and all Local Authorities of  Malaysia.

found to be effective in many countries of the world. It is hoped that this is achieved in as concise a manner as possible, and it is therefore recommended that for more in-depth discussions of the various topics the reader  should make use of the References listed.

It has been estimated that about 350,000 people die in road accidents in developing countries each year. This represents 70 per cent of those killed on the roads throughout the world. In Malaysia there are about 4,500 fatalities and  over 36,500 injured per year. This means that more than 1 person in every 450 of the country will suffer injury or death in a road accident each year. This situation is worsening, and traditionally the "three E's" have invariably been quoted  when discussing ways of tackling the  proble  pro blem m namel namelyy Education, Enforcement and  Engineering A fourth "E", Encouragement (by (by setting targets, support for initiatives, publicity material to promote positive attitudes, etc) has now also been added.

This Guide is designed to be an easytoassimilate outline of procedures that have been

Indeed the Guide has been based on several of  these publications, particularly the Indonesian Accident Investigation Procedures Manual, the Institution of Highways and Transportation Transportation (UK) Guidelines for Accident Reduction and  Prevention2, UK Department of Transport's Accident Investigation Manual3, and RoSPA Road Safety Engineering Manual4. 1:1.1 Summary of contents

Chapter I as an introduction, highlights the scale of the accident problem of Malaysia and  introduces the types of strategies generally applied in many other countries to reduce accidents. The national accident reduction target is quoted and the need to manage road  safety stressed.

Although the most effective approach for many road safety initiatives will be a combination of these elements, it is the

Chapter II is devoted to the accident database of Malaysia, its production, and the responsibilities of all those agencies

Engineering on which this focused. It isapproaches likely that some aspect of Guide is highway design, layout, state of road or traffic control is a contributory factor in most accident occurrence. It is well established that considerable safety benefits may result from the application of appropriate road engineering or traffic management measures at hazardous road locations. In order to reduce accidents effectively and help to achieve the nationally set reduction targets, it is essential that a systematic approach to the identification of  hazards and selection of appropriate treatments  be carr carried ied out at the the loca locall level level thr throug oughou houtt the the

contributing to its content.

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The third and subsequent chapters include a step-by-step approach (totalling 10 steps) to tackling the safety problems within a road  authority's area. These steps are illustrated in the flow chart shown in Fig. 1.1. The three steps of Chapter III comprise the investigation process. A list of the worst  blacks  bla ckspot pot sit sites es need needss to be prod produce uced d first first fro from m the computerised database. Preliminary analysis is described and early initial site visits are also recommended. Page 3

 

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Chapter IV (Steps Chapter (Steps 4 and 5) deals with diagnosis of the problems, including the collection of sketch diagrams and other  available data together with the likely need  to carry out specific site studies. Detecting accident patterns (a skill to be acquired) is introduced.

 points in the network. For example, even at a “high risk” junction in Malaysia having 42,000 vehicles (16-hour count) passing through it and where 53 accidents occurred  in one year with 10 involving injury, the actual accident occurrence rate is still relatively low. These accidents occurred  during about 18,300,000 vehicle

The two steps steps (6 and 7) of Chapter V are concerned with the selection of possible countermeasures and prioritising both these and the sites to be treated. Lists of the most common problems and treatments are included. A method of carrying out cost benefit estimates to assist in i n the decisionmaking process for the most effective measures is also described.

movements. That is, one damage-only accident every 425,000 movements and one injury accident every 1,830,000 movements.

Chapter VI discusses the implementation stage (Step 8), that is detailed design and  installation, briefly, and emphasises the need  for safety audits and for carrying out all

The precise moment when an accident will occur can never be predicted, and even if  long periods such as a year are considered  the numbers will fluctuate randomly about a longer term average. Statistical tests can show whether, during one particular ‘high’ year, a real change has occurred. The occurrence of accidents along the network  tends to be less random as accidents are often clustered at so-called "hazardous

roadworks as safely as possible.

locations" or "blackspots".

The final two steps (9 and 10) in Chapter  VII cover evaluation of the completed  works. Some observational measurements for monitoring the sites are described in  brief. Simple statistical techniques are outlined to estimate the size of the effect of  the measures introduced. All necessary statistical tables are contained in the Appendices, as are examples of the Police POL27 accident report form and UK Road  Safety Plans (see 1:5.1).

1:2 WHA T IS A AC ACCIDEN CIDENT? A fullWHAT definition of ROAD a road traffic accidentT? is: "a rare, random, multi factor event always  preceded by a situation in which one or  more road users have failed to cope with their environment, resulting in a collision on the public highway which should be recorded recor ded by the police".

Although, from the previous section, it may  be concluded that road accidents are far too common in Malaysia (see Section 1:5), they are comparatively rare events at specific Cawangan Jalan, Ibu Pejabat JKR, K.L

There is rarely an accident situation in which only one "thing" or person is truly the sole cause of the accident: hence accidents are multi-factor events. There are three basic categories of factors: 

Road user errors

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

Road and environment faults



Vehicle defects

It has been shown that road user errors are  by far the most prevalent factor but often another factor(s) is present. For example, “adverse environment” implies a situation where a driver has had difficulty manoeuvring a vehicle safely; drivers are frequently provided with insufficient or  unclear information with respect to signs and markings; sometimes poor design can cause a driver to have a misleading visual impression; and occasionally defective tyres and brakes can contribute significantly to an accident occurring. The chain of events leading up to an accident include people’s experiences on that day which can lead to stress or lack of  adequate concentration on the driving task, and ultimately mean one or more  persons failed to copethat with their  environment. An assessment of the factors in the chain could indicate which road and  environment factors may benefit from safety engineering remedial measures. Consider the example of a junction where skidding on a wet road surface has been recorded in several accidents by the police. Care in analysis is needed as an inexperienced investigator may immediately recommend that the skid resistance of road  surfaces on the approaches to the junction need to be upgraded. Careful study of the site (during similar  conditions), however, may reveal that tree  branches weighed down by rainwater tend to obscure road signs and advance warning signs. The drivers thus failed to cope  primarily because of obscured signs rather  than the wet road surface itself. Treating the road surface may still be necessary but would be much less effective if the trees were not cut back or the signs not re-sited  for improved visibility. visibility.

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1:3 APPROACHES TO IMPROVING ROAD SAFETY The main objective of improving road safety through road engineering and traffic management simply means measures taken  primarily to avoid some accidents happening in the future, or at the very least, reducing the severity of future accidents. This may be achieved by following two distinct approaches: (i) (ii)

ACCIDENT ACCIDEN T PREVENTION PREVENTION ACCIDENT REDUCTION

ACCIDEN ACC IDENT T PREVENT PREVENTION ION

Involves the application of safety principles in the planning, design, upgrading and  maintenance of roads. (See ref 5: The safety audit of highways). ACCIDEN ACC IDENT T REDUCTIO REDUCTION N

Involves the application of appropriate road  engineering or traffic management schemes at hazardous locations on the existing road  network. Such applications, particularly those of relatively low-cost, at known high accident locations or “blackspot” have yielded very high returns in many of the more industrialised countries of the world. Although accident prevention plays an extremely important role in maintaining a safe environment, this Guide concentrates on accident reduction and is aimed at engineers and technicians who have responsibility for safety on the existing road  network. It is recommended that for more information about accident prevention the reader refer to ref.6: ‘Towards safer roads in developing countries - a guide for planners and engineers’.

1:4 THE FOUR BASIC STRATEGIES The four basic strategies for accident reduction through the use of  countermeasures are:

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Single sites/Blackspots the treatment of specific types of accident at

a single location [Eg. usually junctions, but could be areas 200-400m in diameter, 300-500m stretches of road] Mass action schemes

The application of a remedy to locations with a common accident problem. [Eg. skidding on wet road surface, head-on collisions, excessive speed approaching roundabouts] Route action plans

The application of remedies along a route with a high accident rate. Area-wide schemes

The application of various treatments over a wide area of town/city. town/city. [Eg. including traffic management and  traffic calming (speed reducing devices) in areas bounded by links on a network, housing areas or l km squares having higher  accidents than a preset level]. Blackspot treatment is likely to be the most Cawangan Jalan, Ibu Pejabat JKR, K.L

effective as amoving startingto  point, theand roadstraightforward authority perhaps the other wider types of application as experience is built up. All these strategies rely on the availability of  data which contains full information about accidents and their locations so that common features which have contributed to the accidents can be identified. Accident data and the use of collision and stick diagrams, key analysis tools for the traffic engineer, are discussed in Chapters II and III.

1:5 SAFE SAFETY TY MANAG MANAGEMENT EMENT One of the most effective initiatives in improving safety has been found to be the setting of realistic accident reduction targets around which all authorities can properly  plan reduction programmes. In 1991 the Government of Malaysia set a national target:- to reduce the number of  fatalities resulting from road accidents by 30  per cent by the year 2000. This was based  on the year 1989 which means, in practise, a reduction from 3773 to 2641 deaths per year  (fig. 1.3). Page 7

 

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This was expressed the special target into (which needs to be targets) to Committee for Roadby Safety in 1990Cabinet in terms national disaggregated State and local of a fatality rate reduction from 7.12 down  be reflected in safety initiatives for each to 3.14 deaths per 10,000 vehicles registered  local area. to be achieved by the year 2000. The somewhat larger percentage reduction For example, Fig. 1.5, from the U.K.’s expressed in the form of fatality rate is due Institution of Highways & Transportation’s to the fact that this takes some account of  (IHT) road safety guidelines, illustrates the the fairly substantial, steady increase in large number of policy initiatives which can vehicular traffic in Malaysia. The  be input into each local area scheme, ie. the assumption was that of continuing linear  integrated approach where agencies need to growth in the number of vehicles registered  co-operate in agreeing targets and plans, and  as that experienced during the past ten years. need to monitor the effects of the safety (see fig. 1.4). work. It can be seen from fig. 1.3 that there is a generally increasing trend in deaths which is  particularly marked in more recent years. This disturbing feature makes it more important than ever for all authorities to work hard to achieve their particular target.

1:5.1 Road Safety Plans

Although aimed at fatalities, it is likely that the accident countermeasures employed will also help to reduce the levels of severely injured casualties.

Sample contents of some annual Plans  published in the U.K. are included in Appendix A. Before producing such a document, the following will be required:

It is recommended that each highway authority produces an annual Road Safety Plan in which the local casualty reduction target is stated and a strategy for achieving the targets is developed.

Safety management should allow the Cawangan Jalan, Ibu Pejabat JKR, K.L

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Interim Guide On Identifying, Priortising And Treating Hazardous Locations On Roads In Malaysia

Review of existing transportation policyhighways and 



Investigation of accident trends for  various road user groups in the authority’ss geographical area authority’



knowledge of the working structure of the authority (relationship  between departments, committees external agencies concerned with safety).

The key to success lies in setting a series of  achievable casualty reduction targets (short and long-term) that can be monitored, and   being able to acquire the increased resources that will inevitably be required.



Summary proposals (including of major capitalplanned schemes, smaller remedial engineering work, safety audit, maintenance, costs, relationships with other agencies, safety publicity, traffic law enforcement)



Methods for monitoring and  evaluation



Report of previous year's work and  effect on accidents

The Plan should be a comprehensive document containing photpgraphs, graphs and figures and should be made available to the public.

The Plan should include: 

Background to the road accident situation in the authority area (accident trends with respect to road  user groups, road features etc)



Aims of the Plan (casualty reduction targets)

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REFERENCES 1.

TRANSPORT AND ROAD RESEARCH LABORATORY LABORATORY.. Interim Interi m manual on accident investigation procedures and the development of low-cost engineering improvement schemes. TRRL, Pusat Litbang Jalan, Ministry of Public Works Works Indonesia, Jalan Raya Timur No. 264, Bandung - 1993.

2.

INSTITUTION INSTITUTI ON OF HIGHWA HIGHWAYS AND TRANSPORTA TRANSPORTATION. Highway safety guidelines: accident reduction and prevention. International edition. editi on. IHT, IHT, 3 Lygon Lygon Place, Ebury Street, Street, SWIW OJS, London - 1990.

3.

DEP DEPARTM ARTMEN ENT T OF TRAN TRANSP SPOR ORT T. Acci Accide dent nt Inv Inves estig tigati ation on Man Manua ual. l. Roy Royal al Soc Socie iety ty for the Prevention of Accidents, Cannon House, The Priory Queensway, B4 6BS, Birmingham - 1986.

4.

ROYAL ROYAL SOCIETY FOR THE PREVENTION OF ACCIDENTS. Road safety engineering manual. RoSPA, RoSPA, Cannon House, The Priory Queensway, Queensway, B4 6BS, Birmingham - 1992.

5.

INSTITUTION INSTITUTI ON OF HIGHWA HIGHWAYS AND TRANSPORTA TRANSPORTATION. Guidelines Guideli nes for: the safety audit of highways. IHT, IHT, 3 Lygon Place, Ebury Street, SWlW OJS, London - 1990.

6.

TRANSPORT & ROAD RESEARCH LABORATORY LABORATORY.. Towards safer roads in developing countries: a guide for planners and engineers. TRRL & Oversea’s Oversea’s Development Admin., Old Wokingham Wokingham Road, RG11 6AU, Crowthorne - 1991.

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CHAPTER II ACCIDENT DATA 2.0 INTRODUCTION An essential element of any accident reduction and prevention strategy is the collection and investigation of road accident data. Accident investigation procedures in the context of this Guide depend on the existence of a reliable database. This chapter outlines the database which is now being established in Malaysia with the microcomputer system that can be used for  analysing this data.

2:1 PRODUCTION OF THE ACCIDENT DATABASE All accident data originates with the recording of details by the police either at the scene of an accident or as subsequently reported to them at the local police station  by those involved. There will inevitably be a substantial number of road accidents that are not reported to the police at all. The accident details are first recorded in the  police officer’s notebook and a simple record is made in the 24-hour incident book  at the police station in which a unique reference number is assigned to the accident. If human injury has occurred and/or a  prosecution is likely, an accident investigation file is opened, again having a reference number. This contains all documents associated with the accident, eg. witness statements, photographs, description and sketch diagram of the scene as found by the police reporting officer. This file is required in the law courts in the event of a  prosecution. The traffic accident report form, POL27 (Pin. 1/91), is a pre-printed standard form and is the basis of all computerised data. It is also completed by the police accident reporting officer. officer. The form comprises 15 pages, though Cawangan Jalan, Ibu Pejabat JKR, K.L

several pages are repeated (for reasons given  below): see copy of the form included in Appendix B. The first page contains some brief general instructions on filling in the form, though full instructions are contained in a separate  booklet (Panduan Mengisi Borang POL271). Data entry begins on page 2 which includes information of a general nature, such as the  police station, accident reference number, time and date of the accident, number of  vehicles and casualties, road type and  condition, road geometry, collision type, weather and lighting conditions, etc. This page also contains a small section for  information on the closest kilometre post to the accident. This important page of the POL27 form is repeated twice (on pages 3 & 4) such that carbon paper can be inserted to  produce copies for the Police District and  also the local JKR office or local government department (see Section 2:3). The second main page (page no. 5) provides space for details of the vehicles involved in the accident including their type, model registration number, damage suffered, defects, and their movement prior to the collision. The details of the vehicle’s driver  or rider are also included on this page. These include or herany age,driving sex, licence, (if any),his whether errors injury were made and whether they were wearing a seat  belt or crash helmet. This page of the form is repeated for up to three vehicles involved in the accident with an additional carbon copy of each for the Police District. If more than three vehicles are involved then the reporting officer  simply needs to attach additional pages, as necessary. The next new page (page 11) deals with any passengers or pedestrians involved in the accident, where again Page 11

 

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simple details such as age, sex, severity of  injury, are recorded. The remainder of this  page contains estimates of the cost of  damage to vehicles and/or property, and also codings for the location of the accident (see Section 2:2). Space for up to twelve injured passengers and six pedestrians is included on this page, where a carbon copy

recording the coding for both systems for  each accident also serves as a cross-check  on the accident location (it has been found  elsewhere that errors are often made in the recording of grid coordinates).

is again provided for Police Headquarters.

i) ii) iii) iv) v)

The final page (page 13) includes a short space for the reporting officer to describe how the accident happened. Another box is  provided for a sketch of the accident including the position of the vehicles prior  to the collision, and the collision point in relation to the road layout. Separate space is  provided for a location sketch where a simple map should be drawn showing clearly where the accident occurred on the road network.

Roads in Malaysia are one of five categories: Expressway (Toll) Federal State Urban Other (District Council or private)

2:2.1 Rural Areas

For rural roads (types i,ii,iii or v above), kilometre posts should be used as the network coding system. The Police reporting officer should estimate the position of the accident (to the nearest 100m) from the closest kilometre post. On Expressways this task is made easier as 100m posts have also

Two carbon copies of this last page are  provided for both the Police District and the local JKR District Office or Local Government Department. The original/top copy of the form is sent to Police Headquarters in Kuala Lumpur. Lumpur.

 been installed.

2:2 LOCATION CODING Location coding is a very important feature of the accident data as it provides the only way in which an engineer can obtain a true  picture of where his safety problems exist. Two methods of location coding have been adopted in Malaysia and these are:

2:2.2 Urban Areas

1. 2.

Network coding Grid coordinate coding

The national grid coordinate system should   be included on all maps used such that the  position of the accident can be read off  easily.

For urban areas (types iv or v above), a  Node system needs to be devised where each major road junction is given a unique number (for that particular map). Sections of road between junctions are known as Links and can be uniquely  by the node numbers on each side of defined  the accident.

The function of the Network coding is to  provide a means of examining easily and  reliably a particular route or junction, or  listing those with the worst accident records. The Grid coordinate coding provides an absolute location reference and means of   plotting accident maps (essential for  Geographic Information Systems).

Where an accident occurs off the main road  network the location can be approximately defined by a unique Cell number. Cell numbers are simply areas containing smaller  roads (eg. housing areas) which are normally bounded by the main road network, and should be assigned a different numerical sequence (eg. 900-999).

As well as facilitating both analysis feature,

Again, the national grid coordinates must

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also be recorded by reading off values on the appropriate map.

2:3 RESPONSIBILITIES WITH RESPECT TO ACCIDENT DATA The production of the accident database for  Malaysia is shown diagrammatically in Fig. 2.1. and the responsibilities of various authorities are outlined in the following sections. 2:3.1 Police

As mentioned above, when the local police station has completed a POL27 form according to their coding instructions1, the top copy is sent to the Police District Office, where it is checked, and then sent on to Police Headquarters at Bukit Aman, Kuala Lumpur. In practise, this tends to be done in  batches, normally each week. At the same time pages 4 and 15 of the form are sent out to either the local JKR District Office or the

of each accident and complete the coding of: 

Route number 



Lowest Section number of km posts on either side of accident



 Nearest 100m from the above post



Relevant map code and series



X-coordinate (easting)



Y-coordinate (northing)



Direction in which vehicle at fault was travelling

In order to provide this data the JKR Office will first need to acquire 1:25000 scale topographical maps of their area. Ideally with the use of a calibrated measuring wheel

Local Government Office, as appropriate.

attached to a car, all State and Federal roads in the area need to be driven along slowly and logged; ie. the position of kilometre The forms are further checked for   posts and other landmarks in relation to completeness at Bukit Aman and then reference points already marked on the map  processed (with other crime records) for  (eg. road junctions) are noted as accurately entry onto the mainframe computer. At the as possible. On average, a feature or  end of each month, the accident file is downloaded to a microcomputer diskette and   permanent land-mark should be noted at least every 1/4km. the data-file converted into the Transport Research Laboratory's Microcomputer  Accident Analysis Package2 (MAAP), which This information can then be transferred to the maps: an example of part of such a map has now been adopted as the standard  is given in Fig. 2.2. If not already shown, accident analysis tool for Malaysia. one kilometre squares also need to be 2:3.2 JKR

The responsibility for precise location coding for each accident now lies with the various road authorities, as this is of primary importance to them. This is why copies of   pages 2 and 13 (ie. pages 4 & 15 containing road number, kilometre post and collision sketches) of each accident are either  delivered to or collected from the JKR  District Office or Local Government Offices for completion of the relevant sections.

accurately drawn maps grid  corresponding to the position of on the the national coordinates. With the additional landmark information and using the Police descriptions and  location sketch on the POL27 form, it should now be possible for the JKR engineer  to pinpoint accidents much more easily on the appropriate map, and thus fill in the aforementioned location data.

The appropriate officers at the JKR District Office are required to check location details Cawangan Jalan, Ibu Pejabat JKR, K.L

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At the 1:25000 scale, just be  possible to record the it X should and Y coordinates for each accident location to the nearest 10m (though the error may be ±25m). All completed forms should be sent to the Highway Planning Unit (HPU) of the Ministry of Works Works in Kuala Lumpur every month. 2:3.3 Local Government

For towns or cities it has been found to be more practical to use a node system. The Local Government Department are thus required to complete the following information on the POL27 forms sent to them: 

Route number (where one exists)



Relevant map code and series



X-coordinate (easting)





Y-coordinate (northing)





 Node number side of accident (if notonatother junction) Direction in which vehicle at fault was travelling

Again this requires the production of special maps, in this case producing a standard node system. For town/city maps a scale of  1:5000 (or at most 1:10000) is recommended. The Local Government Department should then assign a unique node numbering system preferably to all  junctions in the' city. An example of part of  such a node map is shown in Fig. 2.3. Again, if not already shown, squares corresponding to the national grid should be accurately drawn on the maps. (preferably 100m grid squares). This will enable X-Y coordinates to be noted easily to an accuracy of 10m. All completed forms should again be sent to HPU on a monthly basis

 Node number of accident or nearest node (if not at junction) or cell

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2:3.4 Ministry Of Public Works

On receipt of the completed parts of the forms (pages 4 and 15) the location information is further checked by HPU and  entered with the accident identifying  parameters onto computer. This will eventually be merged (once per  month) with the corresponding accident records received from the Police (see Fig. 2.1). In theory, the database is now complete and can be sent out in the form of relevant MAAP data files for for use by the road  authorities or analysis by other interested  groups.

and safety improvements). For larger larger scale safety improvements it is recommended that central government  provide a Special Road Safety Fund from which road authorities can apply for grants supplementary to their annual budget. The application will, of course, need to be  justified for each scheme in terms of  expected accident reductions which will contribute to achieving the local target.

2:4 RESOURCES REQUIRED In order to be successful in not only maintaining the accident database but achieving the local casualty reduction targets, resources will be required for both capital expenditure and staff time. Both the Institution of Highways and  Transportation (IHT)3 and Local Authority Associations4 in the UK strongly recommend that a local road authority should establish a specific Accident Investigation Unit for this data maintenance, analysis and engineering side of accident reduction and prevention. The advantage of  such a group is that it can dedicate its time to the task and not be diverted onto other  traffic or highway matters. The IHT Guidelines suggest suggest a staffing staffing level of one engineer or technician for each 4001000 reported accidents per year, depending on whether the Unit can pass detailed design and implementation of schemes to another  section. The staff must be trained as safety engineering is a specialised area of work. Adequate capital resources are also required  in order to implement the extensive remedial work necessary to meet the local targets. It is therefore recommended that a set amount  be specified in each annual budget of the road authority which is reserved solely for  safety expenditure (maintaining the database Cawangan Jalan, Ibu Pejabat JKR, K.L

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REFERENCES 1.

POLIS DI RAY RAYA MALAYSIA. MALAYSIA. POLIS 27 (Pindaan 1/91) - Panduan Mengisi Borang. Cawangan Trafik, Ibu Pejabat Bukit Aman, Kuala Lumpur - 1991.

2.

HILLS, B L, G J ELLIOTT & D CLARKE. Microcomputer Accident Analysis Package v5.0 (MAAPfive) User guide. Transport Research Laboratory, Overseas Centre, Crowthorne - 1994.

3.

INSTITUTION INSTITUTI ON OF HIGHWA HIGHWAYS AND TRANSPORTA TRANSPORTATION. Highway safety guidelines: accident reduction and prevention. International edition. editi on. IHT, IHT, 3 Lygon Lygon Place, Ebury Street, Street, SWIW OJS, London - 1990.

4.

LOCAL AUTHORITY ASSOCIATIONS. ASSOCIATIONS. Road safety code of good practice. C/o Hertfordshire County Council, Highways Dept, North Road, Hertford, SG14 2PY, 2PY, U.K. - 1989.

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CHAPTER III INVESTIGATION 3:0 INTRODUCTION The following chapters contain a stepby-step approach to tackling the problem of  hazardous locations on a regular basis.

This Guide assumes that a microcomputer, the MAAP software (see 2:3.1), and relevant datasets are available to the investigator  3:1.1 Ranking blackspot sites

The main objective of this engineering safety work is to change the road  environment in the most efficient manner  (ie. within a specified budget) such that the maximum benefit in terms of accident savings is gained. This chapter is concerned  with finding out where problem locations exist and the preliminary investigation required to try to determine the nature of the safety problems. Step 1: Identifying And Prioritising Sites

3:1. ACCIDENT ACCIDENT DA DAT TA SEARCH It is necessary to identify high accident sites in the network for which the road authority has responsibility. Ideally, Ideally, a period of 3 to 5 years of accident data should be reviewed. This is because accidents, even at very hazardous locations, are relatively rare events having a considerable random element, particularly in the time at which they occur. Statisticians tend to agree, therefore, that as a general rule, three years is really the minimum period needed to smooth out any abnormally large random fluctuations, to produce a reliable ranking of  hazardous sites, and eventually to make evaluations of the treatments (ie. compare with a 3-year ‘after’ ‘after’ period). period). However, if such a long period is not yet available on the local computer database, rather than wait for this time to elapse, shorter periods can be investigated as long as caution is exercised over the conclusions made.

The first stage is to study the data in a logical manner to rank problem sites. It is important to note at this stage that the initial listing will need to be modified to produce one of ‘treatable’ sites. For example, consider Fig. 3.1 (a) and (b) summarising accident data types for two roundabout sites with similar accident numbers. In (a) there are a large number of similar accidents involving loss of control or skidding during the hours of darkness. This may well be treatable by improved skid resistant surface or drainage, improved signing and lighting. However, at site (b) there is no obvious dominant pattern; thus only site (a) can therefore be classed as a treatable site. It important to try to define a “reaction level” * , ie. the number of accidents or   points above which the investigator takes some action. The reaction level is set based  on the following three variables: 

 Number of accidents: a) all injury accidents  b) severity points weighting c) all pedestrian injury accidents



Type of highway unit: a) kilometre length  b) within 50m of junction c) links or mid-block accidents d) all roads in a defined area



Time period: a) 12-month periods of consecutive months, (not necessarily a calendar  year) are the normal periods used.

*The Highway Planning Unit's current accident points weighting system is accidents involving  fatality= 6 serious injury = 3  slight injury = 0.8 damage-only = 0.2 Cawangan Jalan, Ibu Pejabat JKR, K.L

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An example of a reaction level criterion could be a blacksite definition of: 9 or more injury accidents, [or 15 points or more], within 50m of a junction, [or on a 200m road section], over the past 3 years. It is probably better to focus on injury accidents in setting a reaction level as these tend to be more reliably reported than damage-only ones. The following sections explain how sites can be ranked according to the four approaches to accident reduction mentioned in Chapter 1. 3:1.1.1 Route action sites

The simplest way of ranking sites, and the one currently recommended for use in Malaysia, is to list them in descending order  of accident totals for either sections of road,

417 (includes 2 fatal accidents) 419 422 415 420 409 (includes 1 fatal accident). If the reaction level for this particular road  authority was set at 9 injury accidents in a 100m section in 3 years (ie. as in Fig. 3.3), the first 7 locations are included in the above list (Table 3.1), though in a slightly different ranking order. order. Taking this a step further, if the severity of  accidents is further taken into account by weighting factors (which are normally related to the average accident cost of each severity level), and damage-only accidents are also included (having a real cost), this results in the ranking shown in Table 3.1.

nodes, or grid referenced cells. Highway authorities elsewhere sometimes use accident rates but these necessitate traffic flow counts to be available at all points on the network, and also tend to give lower  rankings to the high-flow, high-flow, high-accident where potentially more accidents could be saved.

It can be seen that in this particular case, which considers a small 27km length of  road, the same seven sites appear at the top of the list irrespective of the ranking method  used. However, the priority order varies somewhat, and is likely to change again when more indepth investigation is carried  out to determine treatable sites.

To produce a list using MAAP, select the Location option from the main menu bar and  select Kilometr Kilometree & Link/Node Link/Node analysis. analysis. If a  particularrural road is being studied, select either the 1km or 100m analysis option, and 

3:1.1. 3:1 .1.2 2 Single Single site sitess

then anyaccidents Conditions, such as, to include only set those involving personal injury accidents.

data entered onto computer. computer.

The priority listing for single sites in a town or city can be handled in much the same way as in the previous section once a node numbering system has been established and 

For a particular town, town, MAAP can produce a list of the worst nodes or links (mid-block  accidents between adjacent nodes) as in the example shown in Fig. 3.4.

An example of a kilometre plot of accidents for a 27km stretch of Federal Route 1 over a  period of three years is shown in Fig. 3.2 To produce such a list, select the Location (using the Zoom option to specify lkm lengths). A list of the worst 100m sections of  option from the main menu bar and select Kilometre & Link/Node analysis as above. this stretch is shown in Fig.3.3 (using the  Now select Worst Worst node. Set any Conditions, Worst button which will prompt for the such as, to include only those accidents number of sites to include in the analysis). With reference to Fig. 3.2 it can be seen that involving personal injury accidents. Finally Select data files to be included in the the worst kilometres are: Cawangan Jalan, Ibu Pejabat JKR, K.L

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analysis. Once a pass has been made through the data files, the user will be prompted for the number of nodes to include in the list. Again weighting factors can be applied to the different severity levels to obtain a cost-related ranking of sites.

It is often more difficult toaccident rank mass sites because a particular typeaction normally only represents a sub-set of the data at any one site. Thus smaller numbers are usually involved. However, However, the simplest approach is to try to assess the likely accident saving for each mass action plan and rank these, producing a list with the greatest potential for accident savings at the top of the list.

3:1.1.3 3:1.1 .3 Mass action sites

In order to determine sites for mass action treatment it is necessary to relate a selected  type of accident feature to individual sites

3:1.1. 3:1 .1.4 4 Area Area wide wide action action

and to initially the latter according the numbers of rank accidents of the selected to factor.

scattered, andareas, so attention generally tends to turn to wider particularly urban residential areas. In urban areas in Malaysia, it is not uncommon for parts of towns to have well over 100 accidents (and sometimes over 50 injury accidents) per square kilometre per year. year.

Some examples of these would be as follows: Locations with the worst records of:  Accidents on bends  Right-turn accidents  Overtaking accidents   Nighttime accidents  Pedestrians crossing road accidents  Bicycle/motor-cycle accidents Cawangan Jalan, Ibu Pejabat JKR, K.L

As single blackspot sites are gradually treated accident occurrence can be rather 

Again, ranking areas for treatment is not a simple matter and an assessment of the  potential accident savings for each action  plan should be made. Those yielding the  best returns in terms of accident savings related to cost of implementation should be

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made. Those yielding the best returns in terms of accident savings related to cost of  implementation should be placed at the top of the list. MAAP can also be used to produce counts of accidents in grid squares or irregularly shaped areas if a digitised or scanned map (to national grid coordinates) is available and accident locations have also been recorded by coordinates on the database (see Fig. 3.5 example). It is probably best to initially use MAAP MAAP to produce a grid square count and then consider, say, say, ten areas which could possibly each be treated as a package, that is, bounded by roads, railway lines, rivers or other geographic features. This type of ranking is normally carried out  by focusing on the vulnerable road users. For example, total accidents involving some or all of the following groups could be plotted:



  

All motorcycle riders all pedal cyclists Child pedal cyclists (under 16 years) All pedestrian casualties Child pedestrians (under 16 years)

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STEP 2: Preliminary Accident Analysis

3:2. REFINING THE RANKING BY ST STA ATISTIC TISTICAL AL TECHNIQUES Before embarking on an in-depth investigation at any site, it is advisable to check that the site has higher numbers of  accidents than might be expected, and that this difference is statistically significant. The following sections outline some simple statistical techniques which may be used. 3:2.1 Averages or "Norms"

It is important to know whether the level of  accidents is higher than expected, for  example, whether the number of skidding accidents at a site is worse than average. If a particular route is under consideration, this can be divided up into equal lengths (eg. kilometres) and the average number of  accidents per section calculated. This is referred to as the arithmetic mean or norm. To determine whether particular sections warrant further investigation, the standard  deviation (measure of the variability in the data) is normally calculated. The coefficient of variation Cv is a simple measure of how a set of data varies from its mean, with values of Cv > 1 regarded as very substantial deviation.

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Those sites that have more accidents than the mean plus 1 standard deviation should be the first to be singled out for  investigation.

It is used to calculate the probability of a  particular frequency of accidents occurring in a year when the long term average is known.

 Example

 Example

Consider the example stretch of Federal Route 1 shown in Fig. 3.2 and take x as the

Let us assume the injury accident figures for  a site are as follows:

frequency of injury accidents in three years.

1991 = 2 accidents 1992 = 0 accidents 1993 = 1 accident 1994 = 5 accidents If this site is selected on the basis of the last year, it is better to confirm that some change has happened at the site such that the next year will also be high, and not that the apparent increase has occurred by chance. Long term average = (2+0+1+5)/4 =2 Using the Poisson Probability (Single factor  values) tables given in Appendix C, look for  the high year value of 5 in the left hand  column (k=5) and across to the column of  λ(mean) =2. The value here is 0.0361 which means that the probability of 5 accidents occurring where the long term average is 2, is 0.0361 or 3.61 %.

Thus there is considerable variation between 1km sections along this road in their  accident occurrence. Those sections with more than 12 accidents (ie. 6.22 + 6.62) are certainly worthy of further investigation, ie: Section:

417 419 422 419

However, the likelihood of 5 or more accidents occurring at the site should be quoted. To To do this simply add the  probabilities of k=5, k=6, k=7, k=8 etc. That is: 0.0361 + 0.0120+ 0.0034+ 0.0009+ 0.0002 = 0.0526 Thus the probability of 5 or more accidents occurring due to random fluctuation is 5.26%

3:2.2 The Poisson Test

This test (for randomly occurring events) is commonly used to determine whether a recent increase in accidents at a site was due to random fluctuation only (and will return to previous levels). Cawangan Jalan, Ibu Pejabat JKR, K.L

ie. about a 1 in 20 chance that this is random, or a 94.74% (100-5.26) (100-5.26) chance that this is a real increase.

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3:2.3 Chi Squared test

This test is normally used for two purposes: 

To determine whether the number of  accidents of a particular type is "significantly" higher than at similar sites



To check whether there has been a "significant" change in the number of  accidents at a site after treatment has  been carried out.

 Example

A particular junction is suspected of having a poor skid resistant road surface, and has the following accident record: ‘Skidding’ accidents  No skidding reported

=7 =5

For all other similar junctions along this road the accident record over the same  period was: ‘Skidding’ accidents  No skidding reported

= 37 = 178

We need to test whether the skidding accidents are significantly different from what might be expected. The following (2x2) table should be set up:

* N.B.

In the Chi Squared Distribution Table (Appendix D), looking along the line with one degree of freedom (v=1), the value just  below the 9.81 calculated above is 6.64 which is the 0.01 “significance” level, ie. 1%. This means that the chance of getting 7 skidding accidents at a site with a total of 12  by chance is only 1 % (one in data is interrogated. 100 chance). Thus it seems fairly certain that there is some reason why the skidding accidents are occurring at this site 3:2.4 Interpretation of “significance”

The significance or confidence levels of  results from the above statistical tests can be interpreted with the following practical meanings:

The above formula formula allo allows ws for Y Yates' ates' co correct rrection ion which overcome overcomess the inaccuracies inaccuracies which which  could occur with the test when using whole numbers - as with accident frequencies. Also,  note that the test becomes less reliable if any cell has a value less than S.

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it is generally agreed that only results significant at (or better than) the 5% level can be regarded as conclusive. 3:2.5 In-depth analysis - initial stage

Having now obtained a priority list of sites for investigation, it is advisable to produce a “working file” of accidents for each site. This can be done easily easily on MAAP and  means that all subsequent analysis can be carried out of the working file, without having to search the whole database each time the data is interrogated. Use the Find Records option from the main menu bar and choose Find Selected Records. In this menu select Create Working file and  then Set Conditions to extract all accidents for the site under investigation. The conditions to be set may be of the following types: i) Kilometre (Section) No. also set: Road Number Nearest 100m (if possible) ii) Node No. also set: Map code or State and  District and PoliceStation No iii) X-coordinate range and Y-coordinate range The working files should include as many years data as available. Clear, meaningful names should be given to these working files so that they can be easily identified at a later date or by other users. A stick diagram diagram of each site site can now  be produced using these files. This is  produce a “working file” of accidents simply a way of displaying each accident record as a column of data. The purpose of the stick  diagram is toassist the investigator to look  quickly patterns of similar types of accident for which some appropriate engineering solution can be devised. The factors leading to accidents will be dealt with in more detail in Step 5, but at this Cawangan Jalan, Ibu Pejabat JKR, K.L

solution can be devised. The factors leading to accidents will be dealt with in more detail in Step 5, but at this stage the stick diagram gives investigator a “feel” for the types of  accidents occurring and provides an indication of what to look for during the  preliminary site visit. Select Stick from the main menu bar and set any conditions if necessary. It is possible to set up a number of different stick formats if  required. An example of a stick diagram from MAAP is given in Fig. 3.6, where each accident is represented symbolically by a column (or stick) of key information. In this example, a T -junction (and one of the worst blackspots in Seremban), only injury accidents have been included; though it should be noted that there were also 74 damage-only accidents recorded in the 3 year period. It can be seen immediately from the stick diagram that the injury accidents all included the vulnerable road users: motorcyclists and/or pedestrians. Five of the six pedestrian casualties were in fact struck by a motorcycle. Most of the other  motorcycle accidents (75 %) were side impacts or side swipes involving cars emerging from the side road and apparently not noticing or misjudging the motorcycle on the main road. Only two of the 13 injury accidents were in darkness, thus poor  lighting is unlikely to be a particular problem at this site. The initial site visits should therefore concentrate on the turning manoeuvre  problem particularly with motorcyclists, and  also the pedestrian problem.

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STEP 3: Initial Initial Site Visit Visit

capital works programme for the area.

3:3 PRELIM PRELIMINAR INARY Y VISIT The site visit is a very important element of  any accident investigation. The main  purpose of the first site visit is to become familiar with the site and to ensure that available plans are up to date and detailed  enough to identify specific features which may be contributing to accidents; for  example, visibility sight lines, street furniture, buildings.

For operational purposes, the easy sites should be tackled first as they should   provide:

The investigator should identify the manoeuvres indicated in the accident reports and try to visualise the accidents,  particularly those with common characteristics. It might be necessary to make visits at different times of the day, or  in dark and/or wet conditions, in accordance with the factors revealed in the stick  diagram.



good return on money spent;



an immediate improvement in the accident record (- useful argument for allocation of funds for future yes);



an important psychological boost to staff to see successful results from implementation of schemes

It is often possible at this early stage to make a preliminary assessment of the likely causes of certain accident types. The use of photographs taken at driver/pedestrian eye height or an overall view can be an invaluable aid in the office or at presentations to committees. 3:3.1 “Easy” & “Hard” sites

It may now be possible to attempt to further  rank sites even at this stage into whether  they will be easy or hard to treat. This can  be done more accurately later when costs and benefits are estimated. Easy sites are those where effective remedial measures can be readily identified and are of  low-cost. Hard sites are those which do not provide a clear indication of appropriate treatment or  where this is likely to be very costly. In the former case the site should be selected for  further, more detailed investigation if it has high numbers of accidents. In the latter case it may be necessary to include the site in a Cawangan Jalan, Ibu Pejabat JKR, K.L

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CHAPTER IV DIAGNOSIS 4.0: INTRODUCTION This chapter is concerned with collecting further data about the sites now selected for  study, and using these to diagnose what are the common prime contributory factors that help explain how the road users involved in the actual collisions. This in-depth analysis of an accident site, area or group of road users is necessary in order to formulate an appropriate remedial measure. The following sections consider a single site analysis, the principles applying also to mass and route action approaches. STEP 4 Collection Of Further Data  And Analysis 4:4.1 Collision Diagrams

Having produced a working computer file for each site, inspection of all this accident data and relevant police records is essential. It should be related to a plan of the area showing all on-site features relevant to the study period. It is suggested that attention should first be focused on injury accidents (the most reliably reported) unless these are very small in number.If accident  pattems are not obvious from these accidents (discussed below),then it may be helpful to include the damageonly accidents where available. It is strongly advised that the POL27 sketch plms and accident description are retrieved by using the accident reference numbers for each accident.The values of  data items which will uniquely define a  particular accident record are:    

State code District code Police Station no. Year 

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

Accident Reference no.

Copies of the sketch plans of accidents referenced by the above numbers from 1992 onwards can currently be obtained on application from: Accident Research Unit, Fakulti Kejuruteraan, Universiti Pertanian Malaysia, 43400 Serdang, Selangor Darul Ehsan Having obtained these and printed out the computerised record for each accident using MAAP, the next step is to produce collision diagrams at each site by drawing an approximate plan, preferably to about 1:500 scale showing the main site features (eg.kerb lines,street furniture, trees and   buildings,and road markings. Details for this should have been noted/drawn during the initial site visit (Step3). On this plan, the POL27 sketch plans for  each accident should be referred to in order  to mark the positions of the accidents, and  also the approach and intended departure  paths of the vehicles immediately involved. An example of such a collision diagram for  a crossroads where there were 10 injury accidents is shown in Fig.4.1. It is suggested that standard symbols be used  for this as given in Appendix E The most important use of the collision diagram is toprovide a starting point for the classification of each accident into clusters. 4:4.2 Classiflcation Of Accident Types

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could mask underlying factors which can often be treated by simple low-cost remedial action.In practice an accident can be assigned to many underlying factors. For  example, depending on circumstances, the basic single collision type shown in Fig.4.2 might be assigned to any of the following accident factors:    

 



 

Approach visibility restricted  Violation of mandatory sign Overshooting give way line Collision on restart from give way line Obscured give way sign Give way line worn away or  conceaIed by uneven road surface Junction ahead not apparent from side road  Excessive speed of main road traffIc Uneven lighting concealing main road vehicles

This list is not exhaustive, but illustrates the fact that a single collision type can be classified according to many factors or  accident types. Some of these may suggest a suitable treatment whereas others may not Cawangan Jalan, Ibu Pejabat JKR, K.L

thus the aim should be to assign accidents to a class for which there is a remedial action. Unfortunately,, many of these underlying Unfortunately factors will not appear in the accident report or original police file. Let us consider again Fig.4.l where the accidents could be classified as: 2 double cross-overs (crossing both main road streams), a right turn, a left tum off (or  nose-to-tail), and a pedestrian accident. At first sight no distinct accident pattern is revealed and thus no indication of my remedial action that would help. If left here no improvement to the junction would be made. However, after reading the written However, description of the POL27 form it was discovered that all 4 drivers pulling out of  one minor road (fig 4.2) stopped first but collided with a main road vehicle on restart,  because their “view to the right was obscured by street furniture or parked  vehicle”. The rear-end collision in fig.4.1 occurred when the first vehicle braked for a third vehicle emerging from the side road   but whose vision was masked by street

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furniture. Similarly the pedestrian stepped  always necessary to verify and add data to out from behind the same street furniture. the computer grid. In Fig.4.5 additional Hence all 6 accidents could be assigned to information obtained by reading the text the class: “view to the right obstructed”, and  description, looking at the sketch diagrams, thus the necessary remedial action is clear; and observations during the site visit, has ie. remove the obstructions.  been incorporated by adding additional items and symbols (such as the “obscured  vision” and “double cross over” taking into 4:4.3 Searching Searching For A Dominant Dominant Acciden Accidentt Pattern account main road direction). Consider the collision diagram in Fig.4.3 where again on first viewing there does not To help reveal common factors a useful appear to be any pattern which indicates a technique is to cut up the grid to produce treatment. There is a need to re-classify the individual sticks for each accident. These accidents to produce a dominant accident can be rearranges repeatedly on a new sheet type whichcould there be is at least one factorinwhich treated. Thecommon simplest way is to produce a stick diagram and,  because every accident cluster is unique, using a standard stick format may be too restrictive. Such a stick diagram has been  produced manually in Fig.4.4.  Note that although other sticks can be  produced and automatically sorted using MAAP,, the investigator MAAP i nvestigator is restricted to using only the computer computer coded items of POL27. Even if MAAP MAAP or other software software packages were used, manual checking is almost Cawangan Jalan, Ibu Pejabat JKR, K.L

of paper until a pattern is noticed. example of one rearrangement (byAn main road direction and collision type) is shown in Fig.4.5). Pattern recognition is a skill which improves with use. In the example it can be seen that the eastbound and westbound accidents reveal different characteristics. The westbound  direction all possess “visibility obstructed by  parked vehicles and trees” and the remedial action may involve new or enforced parking restrictions and tree lopping.

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On the eastbound approach, all accidents occurred on a wet road surface, the wet surface condition for the whole site being statistically no worse than the ‘norm’. The further data required in this case are skid  resistances and any reasons why the eastbound approach may be wetter than westbound. In the subsequent site visit it was found that skid resistance was indeed  considerably lower on this side due to reinstatement of the west side following extensive utility works. Also, lorries leaving a nearby plant were regularly depositing

 junctions they will increase speed, and  they may use a line of trees or telegraph  poles to gauge the sharpness of a bend ahead  and so judge how much to slow down.

water on the road on the eastern side. Furthermore the “Give way” line on the minor road southern approach was worn away and partly concealed due to a surface depression.

Unfortunately, the road engineer is unlikely Unfortunately, to have the opportunity to interview drivers involved in accidents at a problem site. But  by relating the dominant factors from the  police reports to his own site observations it is often possible to identify contributing defects in the road system.

4:4.4 Human Factors Need To Be Considered

Human factors are important to the road engineer as the roadside environment constantly presents visual cues to the driver  as to the nature of the road ahead. Drivers tend to drive on expectancy in that when they see a wide, straight road ahead with no Cawangan Jalan, Ibu Pejabat JKR, K.L

Sometimes, however, the environment gives false visual cues. These are known as “perceptual traps” and are where some drivers are misled by the visual appearance of the road, commonly failing to recognise the presence of a give way junction ahead  or a bend.

4:4.5 Example

A major-minor cross-roads had recently  been improved on the major road arms  by local widening and installation of  clearly-marked right-turn bays. However,, concern was expressed over the However Page 36

 

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the number of accidents which were still occurring. Only one year of accident data were available, and Fig.4.6 Fig.4.6 gives a MAAP stick  diagram for this period which in this case includes all recorded accidents. It can be seen immediately that most (>90%) of the accidents were either right angle, side or  side swipe impacts which implies collisions  between one vehicle approaching the  junction on the major road and another  along a side arm.

right-angle collision. Ideally, the police accident descriptions should also be read (as should witness statements, if available) to determine whether any other factors could   be added to the stick. It is clear that many drivers in these accidents were failing to give way to oncoming traffic at the stop line, and as no further information could be obtained from POL27, the essential site visit should now be carried out. STEP 5: Site Studies Studies And Analysis

4:5 RELEVANT RELEVANT DA DAT TA FROM SITE Most vehicles classed(DIR=7), as “at fault” werefour  Before embarking on expensive new data travelling westbound though collection studies it is important to ensure of the sixteen accidents involved eastbound  that all existing data about the site has been vehicles. There does not appear to be any obtained. Having studied this, together with  pattern to the time t ime of day or day of week on the accident analysis above, it should then which the accidents occurred. Also there  be possible to decide on studies which are were only four accidents during the hours of  relevant to the actual safety problems at the darkness (the junction is lit) and only one site. accident on a wet road surface. Fig.4.7 shows the sorted stick diagram after viewing the POL27sketch diagrams to determine primarily which direction the main road vehicle was travel1ing prior to the Cawangan Jalan, Ibu Pejabat JKR, K.L

4:5.1 Simple Observation

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that have occurred, and also by driving through the site making the same manoeuvres, the investigator is now likely to  be able to notice new features.

e) Would Would accidents be prevented by the  prohibition of any single movement such as a right turn at a minor road?

Some of the most useful questions an investigator should ask are:

f) Could some of the traffic be diverted to other (safer) streets where problems are unlikely to be transferred?

a) Are accidents being caused by the  physical condition of the road or adjacent  property,, and cm the problem be  property eliminated or corrected?

g) Are night time accidents out of proportion today time ones thus needing special night time protection, eg reflectorised  signs, street lighting or traffic signals?

 b) Is a ‘blind’ corner or restricted sight-line

h) Are there any particular times of day, year 

at a junction responsible? If improvement is impossible, have steps been taken to warn drivers? c) Are the existing signs, signals and  markings performing the job for which they were intended? Have conditions at the site changed since the devices were installed? Are replacements needed? Could the devices be causing accidents rather than preventing them? d) Is traffics properly channelled to minimise accident occurrence? Cawangan Jalan, Ibu Pejabat JKR, K.L

or weather condition when accidents are common? i) Do conditions indicate the need for  additional levels of law enforcement? 4:5.2 Example

Continuing the previous cross-roads example, figs.4.8 and 4.9 show views of the approach to the junction fromeach minor  road arm. The minor road is long and  straight and relatively wide such that approach speeds of some drivers are  probably quite high.

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Despite the fact that there are stop signs, the visual cues to the driver provided by the kerb lines, line markings and light columns suggest that the road is continuous without a  break, whereas it is, in fact, crossed by a major road. It is possible that even if a driver is a regular user of the road, the fact that he has been travelling a considerable distance in a fairly straight line could mean that he is not paying full attention and may thus fail to stop at the junction :there is then obviously the chance of a collision with a major road vehicle of the side impact type which can often result in injury.

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To improve this cross roads the engineer  should concentrate on breaking up the long distance view, such that the illusion of a continuous road is removed. A relatively low-cost method of doing this would be to construct new offset traffic island in the centre of each minor arm carriageway with suitable chevron ghost islands and arrow signs. There is also likely to be a need to shave some area off the existing splitter  islands to maintain adequate road width in the curved chicane created (see Fig.4.10). The carriageway's intersection by the major  road should then be much more obvious to approaching drivers.

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As the junction carries relatively low volumes of traffic (including motorcycles), an alternative treatment could be the installation of aroundabout on which are mounted chevron boards opposite each approach arm. This would also have the additional benefit of slowing down traffic approaching on all arms of the junction (eg.see Fig.4.11).

 Nevertheless, some of the following measurements or techniques would be worthwhile in certain circumstances to  provide justification for decisions on remedial action. Table 4.1gives a list of the more common types of accident problems with studies that are likely to be appropriate. However, it must be noted  studies will not be essential in every case. Further details of site studies can  be obtained from ref. 1 4:5.3.1 Traffic Flow

A range of traffic data can be collected to assist with analysis, and this needs to be appropriate to the task in hand and  comparable with the accident data, eg. same year or particular day of week. To help decide on the most appropriate  provision for a particular manoeuvre (eg. right turners)at a junction, it is necessary to know the numbers of drivers normally making this manoeuvre. Comparing previous counts with more recent ones may reveal some changes in traffic pattern that could help to explain changes in the accident pattern. Although automatic axle counters can be used to measure straight road flows quite accurately,, manual counts will probably be accurately required to obtain turning manoeuvres at  junctions. Although Although time-consuming to obtain, this method has the advantage of   providing more accurate vehicle classifications (eg. for motorcycles, buses). 4:5.3 Other Other Observational Measurements

It is obviously desirable to have as much information about a site as possible when making decisions about how best to improve its safety. It is, however, recognised that additional observation studies may be difficult for some road authorities to carry out for reasons of cost and manpower. Cawangan Jalan, Ibu Pejabat JKR, K.L

If pedestrian accidents are a problem then the engineer will need to know how many pedestrians are crossing the road and where they do s. Guidance on carrying out vehicle flow counts is given in ref.2.

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4:5.3.2 Speed Measurements

4:5.3.3 Photography And Video.

Excessive speed is frequently reported as  being a major contributory factor in accidents, and there can be no disputing the fact that safety margins are reduced and the likelihood of escaping injury in a collision is reduced with increasing speed.

The use of still photography or video taken from various positions (eye height, side or   plan view) can be invaluab1e for   presentations or measurements made in the office.

However, to provide evidence for a suspected speed problem at a particular site, speed measurements need to be taken. Road  surface vehicle detectors linked to electronic timer counters provide accurate spot speed  measurements if installed correctly, correctly, but hand-held radar guns have perhaps proved to  be more popular a method due to their ease of use. However, care needs to be exercised  in the use of radar guns to avoid secondary reflections from oncoming vehicles which can cause incorrect readings. For example, they are usually impractical for busy dual carriageways unless used from an overhead 

Using colour video with a tenth second time display facility taken at various times of day, the movement of vehicles and pedestrians can be studied repeatedly in the office. Studying the road user behaviour in this way can sometimes provide valuable clues as to why accidents are occurring and whether  there are any deficiencies in the site geometry which could be improved. If there are indications from the accident data of, say, a peak hour or wet weather effect then filming should be made in the same conditions. 4:5.3.4 Traffic Conflict Studies

 bridge.

It is often difficult to establish the factors that lead to accidents from accident data accidents, and there can be no disputing alone due to incomplete or unreliable the fact that safety margins are reduced  information. An additional measure which and the likelihood of escaping injury in can assist in the diagnosis of problems a collision is reduced with increasing involves the observation of conflicts or  speed. “near-misses”. Conflicts are those events where there is a possibility of an accident, The siting of a radar meter is very  but where a collision does not occur because important. It must be as inconspicuous as one or more of the parties involved takes  possible so as not to affect drivers, choice of  avoiding action. speed and away from bus stops, parked cars,  junction mouths etc. The meter should be A conflict study is simply a formalised   pointed as straight as possible along al ong the road  method of observing the interaction of  (in line with traffic movement):an error of  10 degrees either way will cause the meter  to under-read by 1 1/2 %. A sample of at least 100 (preferably 200) should be taken comprising all freely -moving vehicles (or platoon leaders) to obtain a good estimate of the true mean and  85th percentile speeds. The standard  deviation of the sample should be about one sixth of the mean. If it is much higher than themean (say, one quarter) or much lower  (say, one tenth), then the measurements should be regarded with suspicion. Cawangan Jalan, Ibu Pejabat JKR, K.L

traffic at a location and recording the more hazardous events. There is obviously subjectivity involved in the identification of  conflicts, and observers do need to be carefully trained to maintain conformity of  results. Several slightly varying techniques have evolved in different parts of the world 3 and a relatively easy-to-learn and reliable technique has been developed over a number  of years by TRL3,4. In a conflict study the numbers of conflicts are recorded and graded according to a scale of severity. This ranges from controlled Page 42

 

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Fig. 4.13 4.13 Collision diagram diagram (accidents (accidents overr 2-year ove 2-years) s) for juncti junction on in Seremban

slight braking to extreme emergency evasive action. The resulting data, usually expressed  in the form of daily rates of particular types of conflict, should be used in conjunction with accident information to identify  particular manoeuvres, road user groups, or  site factors which contribute to a poor safety record. Conflict studies do have limitations to their  use, and advice on the choice of sites, numbers of observers, length of study  periods, etc .is given in ref 4. 4:5.4 Example Of5A Site Study Stu Fig.4.13 (from ref. ) shows thedycollision

diagram over a period of two years for an urban TT- junction between two one-way roads in Seremban. The stick diagram produced by MAAP is shown in fig.4.14 and this has been sorted  according to collision type and severity of  accident. It can be seen that the majority of collisions (33 out of a total 68) are side swipes (including all side impacts). Six of these

involved injury and all 6 injuries were suffered by motorcyclists. These collisions were chiefly between vehicles turning right out of the side road, Jalan Sheikh Ahmad, and merging with main through traffic. It is also likely that the 12 rear-end  accidents were as a result of vehicles  braking for these merging vehicles further  upstream. The other main type of injury accident, comprising one fatal and four  injury, that occurred at or near the junction were between pedestrians and motorcyclists. Pedestrians frequently do not notice the smaller visual area that a motorcyclist  presents compared with a 44 wheeled  vehicle. There does not appear to be any noticeable time of day or darkness effects in the accident pattern. Owing to various tune constraints, only a one day study could be carried out at this junction, but it was decided that this should include collecting data on traffic conflicts, approach speeds, vehicle manoeuvre now and pedestrian road  crossing flows. The traffic flows are shown in Fig 4.15 and main conflict counts in Fig 4.16.

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It can be seen that the merge type of conflict with vehicles from Jln. Sheikh Ahmad was the most common due to relatively high merging flows. Drivers making this manoeuvre, particularly motorcyclist,were frequently observed relatively high merging flows. Drivers making this manoeuvre,  particularly motorcyclist, were frequently observed as possible in order to use either  the access road on the left (Jalan Khalsa see Fig.4.11) or adjoining petrol station. From Figs.4.15 & 4.16 it can also be seen that the frequency of pedestrians crossing the road is very high with a maximum of  890 in one hour. Conflicts with vehicles tend  to occur mostly when business activity is high particularly in the morning.

The proposed accident countermeasures at this example site will be discussed in the next chapter.

Approach speeds of freely-moving vehicles were also measured using radar (see Fig.4.17) with a mean speed of 30km/h and  85th percentile of 37km/h, vehicle speeds were not considered to be excessive. Cawangan Jalan, Ibu Pejabat JKR, K.L

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REFERENCES 1.

RADIN UMAR R S. Panduan Diagnosis dan Rawatan Kemalangan Jalan Raya. To be published by Dewan Bahasa dan Pustaka, Kuala Lumpur - 1995

2.

CHE MAT MAT BAHRI BAHRI BIN HJ KASRI. KASRI. Traffic Traffic Survey Survey and Studies. Studies. Institut Institut Kerja Raya Malaysia training reference: JLN/RA/201/1 IKRAM, Jalan Serdang, 43000 Kajang1989.

3.

ASMUSSEN, E. International Calibration Study of Traffic Conflicts Techniques.  NATO  NA TO ASI ASI Series F: Computer & System Sciences. Springer-Verlag, Springer-Verlag, Berlin, Heidelberg, New York, Tokyo - 1984

4.

TRANSPORT & ROAD RESEARCH LABORATORY LABORATORY.. The Traffic Conflict Conflic t Technique Guidelines. TRRL. Institution of Highways and Transportation, 3 Lygon Lygon Place, Ebury Street, SW1W SW1W 0JS, London - 1987

5.

BAGULEY, BAGULEY, CJ, & RADIN UR SOHADI. The improvement of accident data quality in Malaysia. In: Proceedings of First Malaysian Road Conference 1994. JKR, Roads Branch, Jalan Sultan Salahuddin, 50582 Kuala Lumpur - 1994

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CHAPTER V SELECTION 5.0 INTRODUCTION This chapter discusses the steps of se1ecting a package of possible countermeasures for a site and of prioritising the potential treatments and sites. This is done by simply deciding on appropriate objectives of tile various safety strategies based on achieving satisfactory accident reductions which match or exceed the expenditure planned .

 between RM250,000 and RM500,000. 5:6.1.2 Mass Action Objectives 





STEP 5: Select Select Possible Possible Countermeasures 5:6.1 Objectives Of Countermeasure Countermeasure Scheme

For Malaysia, the precise objectives for the four accident reduction strategies outlined in Chapter I (Section l:4) will need to be decided based on local experience but those adopted in the UK are given below as a guide. The First Year Year Rate of Return (FYRR) is a measure of the net benefits in terms of accident reductions from the scheme expressed as a percentage of the total capital cost. This is defined fully later  in this chapter in Step7. 5:6.1.1 Single Site Objectives 

 

To achieve an accident reduction of  at least 33%at treated sites. To obtain a significant FYRR  To out not the exceeding remedial work at a costcarry per site a fixed  maximum amount

An average FYRR of 50% for schemes should be achievable nationally. nationally. As time goes on schemes with a smaller FYRR may  be worth considering provided that they meet the other two objectives. It is suggested that a maximum of  RM25,000 be an appropriate level for the first application of accident remedial work. Thereafter Therea fter this this maximum maximum may be increas increased  ed  Cawangan Jalan, Ibu Pejabat JKR, K.L

To achieve an accident reduction of at least 15% at treated sites for each  plan. To obtain a FYRR of not less than 40%. To carry out the remedial work at a cost per plan not exceeding a fixed  maximum amount.

The maximum scheme cost is likely to depend on the type of measure used and  the number of sites covered. 5:6.1.4 Area-Wide Objectives 

 

To achieve an accident reduction of  at least l0% within the area covered   by the plan. To obtain a FYRR of 10% to 25%. To carry out the remedial work at minimum cost. The maximum sum will depend on the area size and  inclusion of environmental enhancements.

5:6.2 Treatments

Having identified dominant accident types at a location or area under study, this will hopefully give an indication of an appropriate remedial measure (or package of  measures if there is more than one accident group). It is desirable to consider a number of  alternative proposals for each site. For every  proposal it should be checked that: a) The measures are likely to decrease the type of accident at which it is aimed 

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 b) No further increase in other types of  accident is likely to occur as a result of  the selected measure. c) There are not likely to be any unacceptable effects on traffic movement or the environment. It should be stressed that safety at the site under study should not be the only consideration when choosing an appropriate countermeasure. The effect of that measure on the surrounding network should be estimated. For example, a self-enforcing speed reducing device like a series of road  humps on a local collector road may have the effect of making a large proportion of  drivers choose an alternative route along quieter residential streets. As well as being undesirable by residents of these streets, the safety will also most probably be worsened   by the increased traffic now.

the sum of the individual percentages given in these tables. It is also recommended that reference5  be used as a source of ideas on many other  treatments for typical blackspots, and that the reader keeps up-to-date with new techniques. 5:6.2.1 Example

Let us consider the same example T-junction discussed in detail at the end of the previous chapter (Section 4:5.4|& ref.6). It is clear  that the vehicle sideswipe and pedestrian collisions problems should be where attention is focused in designing remedial action. In view of the former type of  accident tending to involve motorcyclist, it was decided that the best policy would be to restrict the crossing manoeuvre and make all turning vehicles perform more of a merge type manoeuvre. This could be done by first narrowing down the two-lane flow along Jalan Sheikh Ahmad which currently joins The following tables (5.1 to 5.3) give a list of simple, chiefly low-cost, measures for  the main road, Jalan Yam Tuan (see Fig.4.15) into a single lane. This would have general, urban and rural situations which the extra advantage of providing more area have been found to be effective. Where which can be utilised for motorcycle available, the average percentage reduction in accidents that has been achieved 1,2 is also  parking. included. It should be noted, however, that the list is based largely on experience in the A solid delineator kerb kerb was suggested for  3,4 U.K. and Australia and should therefore this purpose as shown in the sketch in only be used as a guide or “ideas” list. It is Fig.5.1.This kerb is extended along Jalan likely that some of the measures will not be Yam Tuan so that the merge is actually applicable in Malaysia and the reduction in carried out further downstream where accidents will almost certainly be different. vehicles are travelling parallel to one It is thus very important that all remedial measures are properly monitored and  evaluated, and results published or at least, centrally recorded so that a similar list based  on actual Malaysian experience cm be built up.

If more than one group of accidents has  been identified at a site, then the remedial work may consist of a package of measures with each one designed to reduce a  particular accident group. It does not, of  course, follow that the total effect of such a combination of measures at one site will be Cawangan Jalan, Ibu Pejabat JKR, K.L

another, and thus main road drivers have a clearer view of merging vehicles. This smoother merge should also help prevent queuing along Jalan Sheikh Ahmad despite its exit now being restricted to a single lane. The solid channelisation, which will reduce the width of the main road slightly, will need to be extended beyond Ja1an Kha1sa and the petrol station to prevent drivers making the immediate crossing manoeuvre to the left hand side (100 to150 vehicles per hour - see Fig.4.14).This relatively small proportion of the traffic will Page 49

 

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however, now need to use a road on the left (slightly further downstream) to access these entries. Two proposals are shown in the concept sketches of Figs.5.l and 5.2 to deal with the  pedestrian conflict problem. The first is to  build a footbridge which would only be feasible between Jalan Sheikh Ahmad and  Jalan Khalsa without affecting existing  buildings. As there are considerable numbers of   pedestrians at present crossing the road  further upstream (Fig.4.14), it would   probably also be necessary to install extensive lengths of pedestrian guard rail to channel pedestrians to the footbridge. This is obviously an expensive solution. The second option of installing a pedestrian refuge, as shown in Fig.5.2, is much cheaper. The refuge should make it easier  Cawangan Jalan, Ibu Pejabat JKR, K.L

for pedestrians as they only have to make gap judgments about one stream of traffic at a time. Also, this refuge, together with the new chicane now already at this point, should also help to slow down traffic in this vicinity.. Large road studs along the vicinity  boundary line of the hatched area and  direction arrows on the refuge would  also be required to help minimise the likelihood of co11isions with the new refuge. As well as being much cheaper this second option is preferred as it is like1y that many pedestrians would not choose to climb the footbridge. 5:6.3 Approaches To To Area-Wide Treatment

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A road hierar hierarchy chy should should be be drawn drawn up by a road authority where residential streets, access roads, local distributors, district distributors and primary distributors are marked together with land-use (see Fig.5.3).

This can then be used as a base map on which to mark road accidents, vehicle and pedestrian flows. There is a wide variety of treatments that can be used in residential areas but good  consu1tation with local residents is always strongly recommended. Traffic calming can generally be regarded as ways in which vehicle speeds can be reduced from an average of 50km/h down to 30km/h.

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The safety objective is to reduce both the number and severity of accidents, especially to vulnerable road users. This is usually done with self-enforcing speed reducing measures like chicanes, traffic throttles, road  humps or speed tables (see Figs.5.4 to 5.9)

The main principle of traffic calming techniques is that they still permit motorised  traffic to use the same route which they are unable to do with more restrictive measures like road closures, turning bans and one-way traffic. Although limited use can be made of  these latter measures (eg.Fig.5.5), they are rarely popular with residents and can lead to accidents being transferred to other areas which become used as “rat-runs”.

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It should be remembered that solutions to a detailed study at a site may not exclusively involve civil engineering works. An integrated approach to improving road  safety should really be adopted whereby road safety education and training may need  to be combined with an engineering measure. For example, the introduction of a new signa1 controlled pedestrian crossing in a village may require a local publicity campaign to inform pedestrians and drivers how to use it together with training for  children in the local school(s). STEP 7: Priortise Treatments Treatments & Sites 5:7.1 Estimating Accident Savings

The standard approach for the ranking of  treatments is to carry out a cost-benefit analysis based on estimated benefits of the scheme and simply place these in priority order on the basis of the best returns. However, if there is currently little or no data on which to make an estimate of the likely effectiveness of a treatment, then  perhaps the best way to proceed is to implement the lowest cost schemes first as these are likely to provide the greatest overall benefit. If the least cost scheme  proves in practice to be ineffective then the a1ternative schemes in order of increasing cost should be tried. In most uses a  pessimistic estimate can be assumed to t o be an average reduction in accidents of around  25-33%of a1l accidents. In these applications it is recommended  that temporary materials be employed  where possible for initial trials; for example,  pre-cast concrete slabs tied together and   pinned to the road surface to try a particular  size and position of splitter island (see Figs.5.10 & 5.11). An economic assessment of projected  schemes is important to ensure that the  benefits likely will be greater than the cost of implementing and maintaining the scheme and that the best value for money is obtained. Cawangan Jalan, Ibu Pejabat JKR, K.L

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There are two methods of economic assessment used for this purpose:

5:7.2 First Year Year Rate of Return (FYRR)

i) First Year Rate of Return(FYRR), and  ii) Net Present Value(NPV)

This is simply the net monetary value of the accident (and any other) savings and  drawbacks expected in the first year of the scheme, expressed as a percentage of tile total capital cost.

Both methods need the following basic information:

FYRR (%) = Benefits (1st year) x 100 Capital costs

a) The capital cost of the scheme.  b) An estimate of al1 benefits (monetary value)expected to result. c) An estimate of all disbenefits.

where benefits = accidents savings + change in maintenance costs(+/-) + change in journey costs(+/-) Unfortunately, at present the only available accident costing used in Malaysia is that  produced in 1985 (see Table 5.4 - from ESCAP7). However, applying national inflation figures However, since that time, figures for 1995 are estimated in Table 5.4; and using the recent numbers of each severity class of accidents in Malaysia, the average cost of an injury accident in 1995 is approximately RM33,000. It is likely that this figure is nevertheless an underestimate, and it is hoped that a study will be conducted soon to determine more up to-date and realistic values for Malaysia. Malaysia. A column for the most most recent national accident costings has thus  been left in Table 5.4. Thus let us consider, as an example, a  junction which had l2 injury accidents in 3 years, and nine of these involve side collisions with drivers overshooting the Stop line - these being the treatable group of  accidents. If the target FYRR is 50%, then the maximum budget for the scheme may be calculated as: %FYRR = Annual Acc. Acc. Saving x 100 Scheme cost 50 = (9 x RM33,000 /3) x 100 Scheme cost

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Scheme cost = RM99,000 x 100 50 = RM198,000 That is, the scheme should not cost more than RM198,000 in order to achieve a 50% rate of return. A more detailed assessment may, may, however, however,  be needed with schemes where traffic accidents and traffic levels are expected to change considerably from year to year. For  example, a scheme with an 80% FYRR may not be worthwhile if subsequent road  closures due to construction of a planned  new road, say, restricts the benefits just one year. 5:7.3 Net Present Value (NPV)

This type of evaluation expresses (in a single lump slim) the difference between costs and benefits of a scheme which may occur over a period of several years. Unfortunately, it would be incorrect to simply assume that year 1 benefit can be summed to obtain the overall benefit over  the life of the scheme. This is because society,, in general, prefers benefits which society occur sooner rather than later. Future  benefits must therefore be adjusted , or  “discounted” before being summed to obtain a “present value”. The current rate used by the Treasury for  highway schemes is l1% which means that for each RM l of benefit occurring this year,

if this also accrues next year then this is valued at 11% 1ess, 1ess, ie.89 Sen. A further  year's delay will reduce the benefit again by 11% of 89 Sen, ie.79 Sen, and soon. These figures can be summed over the life of the scheme to obtain the Present Value Value of  Benefits (PVB). The overall economic worth of the scheme is then obtained by deducting the Present Value of Costs (PVC) {these may also have to be discounted  if they are spread over more than one year}: NPV = PVB-PVC The scheme is only usually considered  worthwhile if this figure is positive. 5:7.3.1 Example Example of NPV assessment.

Let us assume that the expected costs of a  junction redesign will be initially RMl00,000 spread over 2 years with annual maintenance costs over the next 5 years (the life of the scheme) of RM8,000. The benefits are always difficult to estimate and will often require a simple educated  guess. If in this case we assume that 4 injury accidents over the first two years(2 per year) will be saved, and this will reduce to 0.5 per  year following that due to changes in traffic. This equates at present to RM66,000 for two years followed by RMl6,500 for the remaining 3 years. The Net Present Value Value is calculated in Table 5.5 to be RM6,865.

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In cases where the estimated benefits do not vary throughout the scheme, the calculation of NPV is simplified simplified by the the use of  cumulated discount values and these are given for various discount percentages in Appendix F. For example, for a benefit of RM20,000 per  annum over 5 years with reference to Appendix F, F, the net benefit at 11% discount rate would be:



all options are ranked in order of  their NPV/PVC ratio [the highest ratio at the top of the list].

If funds are limited, those with the highest  NPV/PVC ratios are preferable on economic grounds. Table 5.6 shows an example of a remedial works priority programme ranked in terms of the schemes, NPV/PVC ratio for a 5 year   period.

RM20,000 x 3.57 = RM71,400 5:7.4 Priorities For Implementation

The economic criteria for scheme assessment using using the NPV approach are: 

all schemes schemes where NPV NPV is positive positive are worthwhile in economic terms;



for a particular site, the most worthwhile option is that with the highest NPV;

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It can be seen that in this example the  NPV/PVC ratio gives only a slightly different ranking of the sites to that using FYRR. Using this listing, a line can be drawn for a particu1ar budget: in this use RM350,000. The full 1ist of l0 sites could  only be implemented if a budget of  RM500,000 were allocated. If the authority is receiving local political or  other pressures to treat a site which is Page 58

 

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outside this list or below the cut-off level, then the table can be used to point out that resources should be concentrated at the sites where greater benefits are likely to occur. This is more 1ikely to yield the best contribution to the nation’s casualty reduction targets. In some uses a site may be at a location which is included within a major capital works programme such as a flyover or  traffic signals. If the time at which these are scheduled for introduction is fairly close, it may be best to “do nothing” at this stage and  incorporate necessary work within the major  scheme. If, however, the scheme is unlikely to be carried out for 2 or 3 years, then short-term (perhaps lower-cost) measures will probab1y be justified .

current budget period to allow for these minor re-allocations of funds. In practice “easy” sites are normally best tackled first to yield cost effective results as quickly as possible. However, it is likely that the “harder” sites, which may require more staff resources to study extensively, will have high numbers of  accidents. These sites should not thus be put on one side and forgotten about.

For this reason and others which might lead to “s1ippage” in timetables, it is always worth investigating more sites and preparing more schemes than can be carried out in the Cawangan Jalan, Ibu Pejabat JKR, K.L

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REFERENCES 1.

ROYAL ROYAL SOCIETY FOR THE PREVENTION OF ACCIDENTS. Road safety engineering manual. RoSPA, RoSPA, Cannon House, The Priory Queensway, Queensway, B4 6BS, Birmingham - 1992.

2.

ACCIDENT REDUCTION 2000 GROUP. GROUP. Progress Report December 1993. Transportation 2PY, Hertford - 1994.Dept, Hertfordshire County Council, Goldings, SG14 2PY,

3.

NATIONAL NATIONAL ASSOCIATION ASSOCIATION OF AUSTRALIAN ST STA ATE ROAD AUTHORITIES. AUTHORITIES . Guide to traffic engineering practise: part 4-Road crashes. NAASRA, 2, Dind Street, PO Box 489, Milsons Point, NSW 2061-1988

4.

ANDREASSEN, ANDREASSEN, D C. Strategies for safety problems. Australian Road Research Board. Research Report ARR163. ARRB, 500 Burwood Highway, Vermont South, Victoria-1989

5.

TRANSPORT & ROAD RESEARCH LABORATORY LABORATORY.. Towards safer roads in developing countries: a guide for planners and engineers. TRRL & Oversea’s Oversea’s Development Admin., Old Wokingham Road, RG11 6AU, Crowthorne-1991

6.

RADIN UMAR RADIN SOHADI. Analisis Terperinci Kemalangan Jalan Raya: Projek Pilot Seremban, Shah Alam dan Petaling Jaya. JK3P, JK3P, Laporan Penyelidikan  No. 4. Majlis Keselamatan Jalan Raya Malaysia, Wisma Semantan, Jalan Gelanggang, 50490 Kuala Lumpur-1993

7.

ECONOMIC AND SOCIAL COMMISSION COMMISSION FOR ASIA AND THE PACIFIC. Report on improvement of the traffic accident recording and analysis system in Malaysia. UN ST/ESCAP/478, Bangkok-1985

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CHAPTER VI IMPLEMENTATION 6:0 INTRODUCTION Having selected an appropriate measure or   package of measures to deal with the

the technical term for the systematic checking of safety aspects of new schemes carried out on the public road.

accident problems at a site area, the next stage is detailed design andorconstruction. It is not within the scope of this Guide to cover in depth the actual detailed design or   physical implementation. This will generally  be the responsibility of another appropriate department. However, it is essential that the team who made the scheme recommendation continue to be involved.

Although it is assumed that national standards will be followed in any design unless unusual local conditions dictate a departure (which needs special approval), a combination of elements perhaps close to their respective recommended minimum standard, may combine to create safety  problems. Safety audit seeks to address such  problems .

The road safety audit is discussed and  general advice on the safety of construction work noted. STEP 8: Detailed Detailed Design Design And   Installation

At present the UK Institute of Highway Engineers’ Engin eers’ Guidelines Guidelines1 are being applied in Malaysia but these should be amended to suit local conditions as experience is gained.

6:8.1 Detailed Design

6:8.1.2 Aims Of The The Safety Audit

As stated above, the next stage after  selecting an appropriate remedial measure will usual1y be detailed design. This is likely to be carried out by a different unit to those investigating the problems, and is  beyond the scope of this Guide. However, the design drawings will, of course, need to  be based on the proposals/outline plans of  the accident investigators and this same team should also remain actively involved  with the designers. 6:8.1.1 Road Safety Audit

Road safety audit is a means of accident  prevention rather than accident reduction (a change in philosophy to the previous chapters). It is the application of safety experience to ensure that future safety  problems are not designed into new schemes. It is discussed here because ideally an audit should also be carried out on safety remedial work, both at the design stage and  again immediately after the scheme implementation: that is, prior to opening to normal traffic. Safety audit is simply the Cawangan Jalan, Ibu Pejabat JKR, K.L



To ensure that all road schemes operate as safely as possible.



To ensure that preventable potential accident-generating elements are not  present in a completed scheme, for  example ,moving lamp columns to the back of the footway.



To ensure suitable accident-reducing elements are included in the scheme, for example, "anti-skid" surfacing on down hill approach to traffic signals, guard rail and chevron  boards on unavoidably sharp bend, crash cushion before essential solid  structure.

6:8.1.3 Organisation Of Of The Audit

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In a road authority it is likely that safety audit will be carried out within the accident investigation/road safety unit, though  preferably by more than one person. Before deciding on who should carry out the audit the following should be considered: considered: 



The audit team should be independent of the design team. It should contain (and must certainly  be led by) persons with safety engineering experience. A knowledge of design standards is important. Other specialists such as traffic signals and structural engineers may also need to be consulted depending on the scheme. The police may also  be required, particularly in the t he latter stages of the audit, where special road users, requirements may need  consideration.

is overlooked. However, the audit team should not rely solely on these lists. The auditors should imagine “walking” or  “riding” the scheme, and should physically do this at the final audit stage to check, for  example, that signs are of the correct type and in the right place, road markings and  island are correctly placed and that there are no unforseen conflicts between the treatment and other existing site features. Although the audit team should discuss their findings with the design team, a formal report should always be produced. This should state the potential safety problems as  precisely as possible and should include a recommendation or options for  improvement. The recommendation should   be in outline form only and it may be desirable to annotate copies of the original scheme drawings.

6:8.1.4 When To To Carry Out The Audit

The scheme should be monitored and  feedback given to the design team.

Safety audits can be performed at the following stages:

6:8.2 Installation



Feasibility study



Completion of preliminary design



Completion of detailed design



Prior to opening to traffic

As stated above, it is beyond the scope of this Guide to include guidance on all engineering aspects of altering existing road geometry or installing countermeasure devices. This section is thus limited to general advice on maintaining safety during installation. 6:8.2.1 Safety At Roadworks



Other times on an informal basis

6:8.1.5 The Audit Task

Information such as plans, list of standards followed, departures made traffic and   pedestrian counts, and accident records should be collected from the design team. It may be helpful to discuss the purpose  behind the design of the scheme and it is essentia1to carry out a site visit at a1l stages of the audit. Appropriate check lists1 should be used  to systematically ensure no safety problem

Accidents tend to occur at a higher rate at roadworks sites and involve more vehicles than on normally operating sections of the road network. A study of major roadwork  sites in the UK 2 found that, despite the fact that the contraflow sites were genera1ly well signed and laid out, accidents still occurred  1.6 times more frequently than on non-roadworks sections, and the percentage of  accidents involving 4 or more vehicles was 29% compared with only 8% without works. It issuspected that the ratio may be considerably higher than this in Malaysia,  particularly at sites where advance warning signs are poor.

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their roadworks sites. Often with relatively short-term work due to the extra trouble required, warning signs are not set out sufficiently in advance of the works site or  are two few in number: this is particularly hazardous where drivers vision of the site may be obscured by a bend or other traffic. The use of modern electrically-powered  flashing arrow lights mounted on trailers tend to provide a more effective means of  attracting drivers, attention. Attention should be paid to the use of  adequate lengths of “safety zone” or  “buffer space” (see Fig.6.4) which provides an escape area if drivers fail to notice the advance warning signs. Lengths of these zones are specified in ref.3. Also, tapers of traffic cones to close off  a lane before the work area, or to move traffic into other contraflow lanes, are often not made long enough. The standards should again be followed to ensure that the traffic movement is gradual, and thus smoother and safer. 6:8.3 Implementation log

It is important to keep a record of the  precise dates of the beginning and  completion of major parts of the remedial work for all jobs. This is essential for the monitoring of the scheme (see following chapter). Similarly, details of all costs involved, including variation orders, must be kept. The actual costs often differ considerably from original estimates, and this record will facilitate a more reliable cost-benefitanalysis. It is very important, therefore, that countermeasure installations themselves are made as safe as possible. The road  engineer must attempt to regularly enforce contractors to follow the standards laid  down in Arahan Teknik 2C/85 3 for traffic control, temporary signs and work zones at Cawangan Jalan, Ibu Pejabat JKR, K.L

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REFERENCES 1.

INST INSTIT ITUT UTIO ION N OF H HIG IGHW HWA AYS AND AND TRAN TRANSP SPOR ORT TATI TION ON.. Guid Guideli eline ness for for the safety audit of highways. IHT, IHT, 3 Lygon Place, Ebury Street, SWIW OJS, London 1990.

2.

MARL MARLOW OW M, and and R D COOM COOMBE BE.. A stud studyy of th thee ssaf afet ety y of of maj major or moto motorw rway ay roadworks in 1987. Research report RR223. Transport and Road Research Laboratory, Old Wokingham Road, RG11 6AU, Crowthorne - 1989

3.

JA JABA BAT TAN KER KERJA JA RAY RAYA. Man Manua uall on tra traff ffic ic con contr trol ol dev device ices, s, tem tempo pora rary ry sig signs ns and  and  work zones control . Arahan Teknik (Jalan) 2C/85. Cawangan Jalan, Ibu Pejabat JKR, Jalan Sultan Salahuddin, 50582 Kuala Lumpur - 1985.

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CHAPTER VII EVALUATION 7:0 INTRODUCTION Having introduced a countermeasure or   package of measures it is important to

It is essential to carry out the monitoring effectively, not least to avoid the “bad   publicity” which could occur if a road safety

establish thework effectiveness of the safety engineering carried out; first to check  that nothing has gone wrong and that it is working as intended, and later to learn lessons which may influence future decisions on improvements.

scheme was seen to be actually causing accidents.

This chapter emphasises the need to monitor   by observing the changes at the site in operation. To evaluate these it concentrates on accident changes and describes the simple statistical tests needed to obtain. STEP 9 Monito Monitoring ring 7:9.1 Initial Observations

The treated site should be observed  immediately after completion of the construction and regular visits made in the following days, weeks or months until the team is satisfied that the scheme is operating in the way expected. It is strongly advised that my earlier   behavioural measurements that were made during the investigation stage of Step5 (eg, traffic conflict counts, speed measurements, skid resistance) are now repeated as this will lend weight to any argument making further changes at the site or, for indeed,  proving success. It can happen, for instance, that some feature of a scheme may produce an unforseen reaction in drivers which creates a potentially hazardous situation. Monitoring should highlight this problem at an early stage so that appropriate action can  be taken quickly to remove this danger. At best it may be possible to alleviate this danger easily, for example, by a realignment of kerb lines to prevent a hazardous manoeuvre. At worst, it could lead to the complete withdrawal of a scheme and need  to reassess alternative schemes. Cawangan Jalan, Ibu Pejabat JKR, K.L

Recording the results of the monitoring measures is also important to build up a database of types of treatment and the effects they produced to provide information for future safety engineering work. 7:9.2 Measures Used In Monitoring

For monitoring or measuring the effect of a safety improvement, the technique employed  is usually by “before” and “after” analysis. The most important measure of success is, of course, whether the safety work has improved the accident situation at the site. This will always need to be assessed for a scheme and statistical methods for  evaluation will be discussed in the next Step. A simple visual method that that has been used, though is perhaps more suitable for  mass action plans rather than single sites, is that cumulative accident numbers (& types) are plotted together with their cumulative mean. Fig.7.1(from ref.1)is an example of this method of data presentation, and illustrates that the daytime running headlight campaign in Malaysia was apparently being effective in reducing those accidents related to daytime conspicuity (MSTOX = motorcycles moving straight or turning when other  road users cross their path), whilst having no effect on night-time accidents. In the table of Fig.7.l the cumulative mean number of  related accidents has been calculated. The cumulative mean is obtained by simply adding on the average monthly accident frequency over the before period (in this case 6 months) to each month after the first one. As long as the standard deviation is not large, the two comparable lines of Page 66

 

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cumulative accidents and cumulative mean accidents lie close together during the  before period, but after implementation of the scheme the cumulative mean line represents what would normally be expected  if no action had been taken, and the amount they drift apart (marked * in Fig.7.1) represents the effect of the measure. However, to be sure that the random nature of accidents has been taken into account, it will normally be necessary to wait for  several years for a valid result to be available. More immediate feedback is often necessary which is why the above method is suggested. Other behavioural data, as mentioned in 7:9.1, can also be collected to give indications that a scheme is working. It would, of course, be impractical to carry out detailed behavioural studies for all minor  alterations, but studies may be particularly important for expensive schemes like areaCawangan Jalan, Ibu Pejabat JKR, K.L

wide or mass action treatments. It must be noted, however, that non-accident variables have the disadvantage that they do not give direct measures of the size of safety improvement. There are practically no variables for which the precise relation to accidents is known. This means that a measured reduction in mean speed, for  example, cannot be translated into an estimate for the number of accidents saved: this is a considerable drawback. However, before carrying out a behavioural However, “after” study it is generally better to wait for  a period of about 2 months after the scheme has been operating. This serves as a “settling in” period during which regular users get used to a new road feature and any learning effects have disappeared. Some of the factors that may need to be examined (see also Step5,Chap IV) are noted below: Page 67

 

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7:9.2.1 Speed Of Traffic

7:9.2.5 Public Perception

If speed reduction is one of the objectives of  the scheme then speeds should obviously be monitored. Similar and appropriate locations should be carefully chosen for the before and after studies preferably using automatic equipment. If radar guns are used then these need to be unobtrusive otherwise warning signals invariably given by drivers in the opposing direction will yield unreliable results.

Often one of the main reasons why an area-wide scheme has been implemented is due to campaigns by residents for something to be done. One of the most important parts of an area-wide scheme, therefore, is public consultation .Thus, an important monitoring measure is how the residents and other road  users feel about the safety elements of the scheme after implementation. 7:9.2.6 Effects On Other Other Areas

The t-distribution can be used to compare whether my changes in the mean speeds in the two periods of measurement are statistically significant (see Appendix G).

It is important to examine whether the scheme has led to an increase in accidents, traffic speeds and volumes in adjacent areas. 7:9.3 Control Data

7:9.2.2 Traffic Conflicts

As mentioned earlier these are generally of  use at junctions only. The “after” study should be carried out in the same conditions and for the same periods as the “before” study,, and preferably using the same study observers (to minimise subjectivity between individuals). The frequencies of occurrence of conflicts cm be analysed in the same way as the methods used for accidents, as outlined in the next Step. 7:9.2.3 Traffic Volumes

If the measure is expected to affect manoeuvres at a junction or drivers choice of route in any other way, then it is desirable to collect traffic flow data throughout the local network. It may also be necessary to expand this survey to provide origin and  destination information so that estimates in through-traffic can be obtained to determine how this has been affected by the scheme. 7:9.2.4 Travel Times

In some cases monitoring may require an estimate of changes in travel time for  residents and through-traffic. This will be important where traffic severance forms part of the scheme, and traffic is being re-routed.

In most of the above monitoring measures (and particularly accident changes) it is necessary to take into account other factors not affected by the treatment which might also influence that measure. Examples are: a change in speed limit on roads which include the site; national road safety campaigns; traffic management schemes which might affect volume of traffic. These changes may be compensated for   by comparing the same “before” and  “after” periods with accidents (or other  measurements) at “control” sites which are untreated. Control data can be either by matched pairs or area controls. A matched pair control control site should be similar to the treated site in general characteristics and also geographically fairly close to it (but not close enough to be affected by my traffic diversion). This is so that the control will be subject to the same local variations which might affect safety (eg. weather, traffic flows, enforcement campaigns). Although the matched pair is the best statistical method to use, in practice it is very difficult to find other sites with the same problems which are left untreated   purely to carry out statistical tests. Area controls which comprise anumber of sites are, therefore, much more frequently used.

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when choosing control sites: 

they should be as similar as possible to treats sites;

that due to other sources. Some of the other  factors that need to be considered are discussed below:7:10.1.1 Changes In The Environment



they should not be affected by the treatment;



there should be more than 10 times the number of accidents at the contorl sites.

For example, if the traffic signals at a site are modified then a control group of sites might be a11other signalised sizes in the town. But if there were only two other  signalized junctions and these had lower  flows and much fewer accidents as did other  uncontrolled junctions, then it would be  better to use all signalized junctions in the State.

This feature was mentioned in the last section of Step 9 whereby a change in the environment or driving habits can affect the accidents occurring at the study site. For  example, a change in the nationa1 speed  limit for the class of road at the site, or  closure of a nearby junction to the site  producing a marked change in traffic t raffic  patterns. This feature can be taken into account by the use of control site data but for this to be valid it is important that these other sites experience exactly the same changes as the site under evaluation. 7:10.1.2 Random Fluctuation

As explained in Chapter I, the rare and  random nature of road accidents can lead to quite large fluctuations in frequencies 7:10.1 The Effect On Accidents occurring at a site from year to year, even This step of the procedure focuses on evaluation of whether the treatment has been though there has been no change in the underlying accident rate. This extra successful in achieving its objective of  variability makes the effect of the treatment reducing the number of accidents. This therefore requires comparison of the number  more difficult to detect; but a test of  statistical significance can be used to of accidents in the target group before the determine whether the observed change in treatment with the number after treatment accident frequency is likely to have occurred  (with the assumption of a similar before  by chance or not.  pattern if nothing were done), and to study whether my other accident type has 7:10.1.3 Regression To The Mean increased. This effect complicates evaluations at high accident or blackspot sites in that This Guide does not attempt to delve deeply accidents at these sites tend to reduce even into the different statistical techniques, but when no treatment is applied. Even if a to suggest practical and simple ways in 3.year total is considered at the worst which schemes can be evaluated. The accident sites in m area, it is likely that the following sections generally refer to “a site” accident frequencies were at the high end of   but the same techniques can be used for  the naturally occurring random fluctuations, mass, route and area-wide action as long as and subsequent years will yield lower  appropriate control groups are chosen. numbers. This is known as regression to the mean. The main problem when using accident data for evaluation (even assuming high recording accuracy) is to distinguish  between a change due to t o the treatment and STEP 10 Evalua Evaluation tion

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As an example consider Table Table 7.1 which gives the actual numbers of recorded  accidents involving personal injury for 122

The effect does, however, tend to be diminished if longer periods of time are selected. For example, Abbess et a1.3, in a

nodes in the town of Seremban over a two year period. For sites with 5 or more accidents in year l there were overall fewer  accidents in the following year. Conversely, Conversely, sites with 4 or less acc1dents have more accidents in year 2. If an accident countermeasure had been installed at the worst 9 sites at the end of year l then a highly significant reduction of 37% might be claimed after year 2, even though the measure had been completely ineffective (this same result would be obtained by doing nothing). An even higher false resu1t would   be obtained if the other 113 sites were used 

study in two counties of the UK calculated  that regression-to-mean had the following effects at high accident sites(ie. more than 8 injury accidents per year), on average, on their accident rate:-

as a control group.

Due to the uncertainty andreliably complexity of allowing for this effect at any site it is suggested, therefore, that where the highest accident sites are chosen for  treatment, then the above order of allowance should be made when calculating any estimate of the actual reduction in accidents the countermeasures have produced.

Possibly the most straightforward way of  allowing for both the regression to mean effect and changes in the environment would   be to use control sites chosen in exactly the same way as the treated sites, and identified  as having similar problems, but left untreated. In practice, it is both difficult to find matched control sites and, if  investigated, to justify not treating them. There has been much debate among statisticians over many years on this subject and the best way to deal with it (see refs. 2,3,4,5). Cawangan Jalan, Ibu Pejabat JKR, K.L

Period of accident data considered  1 year

Regression to mean change in annual accident rate 15 to 26%

2 year

7 to 15%

3 year

5 to 11%

7:10.1.4 Accident Migration

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treated site giving an apparent transfer or  “migration” of accidents. It can be detected by comparing the accident frequencies in the surrounding area before and after implementation of treatments at sites in the area with a suitable control. It is unclear precisely why this effect occurs but is suspected that drivers are “compensating” for the improved safety at treated sites by  being less cautious elsewhere. Again, there are no established techniques yet available to estimate this effect for a  particular site. The first reported occurrence of this feature 6 found an overa1l increase in surrounding areas of about 9% and a later  study8 of a larger number of sites estimated  0.2 accidents/site/year acci dents/site/year..

7:10.2 Before And After Periods

There are a number of points to taken into account when choosing periods to compare  before and after the treatment was applied:



Whilst again the extent of this effect is extremely difficult to monitor, the engineer  should be aware of the possibility of risk  compensation when introducing countermeasures. For example, a scheme giving pedestrians more apparent priority using speed tables or raised pedestrian crossings (which give the impression of  extensions to the footway) may lead the  pedestrian into taking much less care in crossing the road. For further reading on this subject see references 9,10.

that at the control site. The period during which work was carried out should be omitted from the study. If this period was not recorded precisely, a longer period  containing it should be omitted.



The before period should be long enough to provide a good statistical estimate of the true accident rate (so as to remove as far as possible random fluctuations).It should not, however,, include periods where the however site had different characteristics. Three years is widely regarded as a reasonable period to use.



The same applies to the after period  which ideally should also be three years. However, results are often required much sooner than this. A one year after period can initially be used if there is no reason why this should bias the result (as long as the same period is used at the control sites). However, sensitivity is lost and the estimate of the countermeasure’ss success should be updated  measure’ later when more data becomes available.

7:10.1.5 Risk Compensation

This is an even more controversial effect, though related to the previous section. The  philosophy of “risk compensation” or “risk  homeostasis theory” suggests that road users will change their risk-taking behaviour to compensate for any improvements in road  safety. That is, road users tend to maintain a fixed level of accepted risk, so will take more risks when given greater accident  protection, for example, if provided with seat belts or anti-lock brakes.

Before and after periods at the treated site should be identical to

7:10.3 Standard Tests On Accident Changes

In evaluating a treatment the answers to the following questions will usually be required: 

Has the treatment been effective?



If so, how effective has it been?

It is assumed that the user of this Guide will Cawangan Jalan, Ibu Pejabat JKR, K.L

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need to interpret accident data practically without necessarily understanding the underlying statistical theory. For this  purpose it is sufficient to assume that the  before and after accidents are drawn from a normal or Gaussian distribution. This means that we can use the Chi-square test to answer the first question above, ie. whether the changes at the site were statistically significant. However, let us first consider the size of that change by using the k test. 7:10.3.1 The k Test

It is possible that although accident levels reduced at a treated site in an “after” period, the general level of accidents is also reducing; the “real” reduction at the site due to the treatment thus being less than the actual numbers observed (ie. over estimating effectiveness). Conversely, Conversely, if the general level of accidents is increasing an underestimate of the treatment would be obtained. The k test can be used to show how the accident numbers at a site change relative to control data. For a given site or  group of similarly treated sites, let:a  b c d then

= before accidents at site = after accidents at site = before accidents at control = after accidents at control k = b/a d/c

If k < l then there has been a decrease in accidents relative so the control; if k = l then there has been no change change relative to the control; and  if k > 1 then there has been an increase relative to the control. The percentage change at the site is given by

Example:

Let us assume that Table 7.2 gives the annual injury accident totals for a priority T-junction in a semi-urban area which had  Stop on the minor originally, but wheresigns a roundabout wasroad installed three years ago. The control data used are accidents on all other priority junctions in the District over exactly the same 6 year period.

Therefore, as k < 1there has been a decrease in accidents relative to the controls of:

or, if any of the frequencies are zero then 1/2 should be added to each, ie: Cawangan Jalan, Ibu Pejabat JKR, K.L

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7:10.3.2 The Chi-Squared Test

7:10.3.3 Group Of Sites With Same Treatment

It is important to answer whether the above change in accidents was indeed produced by the treatment or whether this occurred by chance. This test thus determines whether  the changes are statistically significant. with reference to the above table chi-squared 

For a number of sites, N, which have had  the same treatment, the overall effect is a rather more complex calculation, ie. by solving the following equation for K  over all the sites, ie. i = l to N. The other symbols

is calculated by the formula:

are as in previous equations.

For testing, the natural logarithm of a variable such as K  is usually found to have a more symmetrical distribution (amenable to standard statistical treatments), and the standard error, σ, of loge K  can be approximated to the following:

Example:

 Now looking at the chi-squared distribution table (Appendix D) and the first line (one degree of freedom, v=1), the value for chisquare of 5.38 lies between 3.84 and 5.41. This corresponds to a value of significance level (on the column header line) between 0.05 and 0.02, which is normally quoted as greater than the lower level, ie. better than the 5% level of significance. This means that them is only a 5% like1ihood (or l in 20 chance) that the change in accidents is due so random fluctuation. Another way of stating this is that there is a 95% (100% - 5%) confidence that a real change in accidents has occurred  at the junction.

The following ratio should then be calculated using loge of the value of K  calculated above and its standard error from the previous equation:

±

and if this t), value outside theisrange 1.96 (Student's thenisthe change statistically significant at least the 5 per cent level.  Now to test whether the changes at the treated sites are in fact producing the same effect on accident rates, calculate the following chi-squared value.

The 5% level or better is widely accepted as the level in which the remedial action has certainly worked, though the 10% level can  be regarded as an indication of an effect.

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If this is significant with N-l degrees of  freedom [refer to the (N-1)th] row in the table of Appendix D, where N is the number of treated sites], then unfortunately, the changes at the sizes are not producing the same effect. If non-significant, then it is likely that they are producing the same

to the treatment is negligible, the First Year  Year  Rate of Return (FYRR) is simply given by:

effect.

The above FYRR should be rounded  so 90% to give m figure indication of the possible effect of using this treatment in the future.

7:10.4 Economic Evaluation

For every scheme the evaluation should  include an indication of the benefits actually achieved in relation to cost. In the previous sections we have already seen how we can determine a best estimate of the size of the effect on accidents. Considering again the example in Fig.7.2, the estimate of the reduction was 72.2%. If  the site was one of the worst blackspots in the District, then we ought to make some allowance for 7:10.1.3,let the regression-to-mean effect. From Section us assume this amounts to as much as 11%, such that our   best estimate of the true reduction in accidents due to installation of the roundabout is 61.2% (72.2%-11%). (72.2%-11%). Since the original number of accidents at the site was 20, this represents a saving of  12.24 accidents over the study period. As the “before” period in this case was 3 years, the  best estimate of savings is 4.08 accidents per  year. It should be noted that only injury accidents have been considered here but if there had   been reliable numbers of damage-only accidents which were also reduced, then a separate costing of these should perhaps also  be carried out. Using the average injury accident cost of RM 33,000 used in Step7 (see Section 5:7.2), this accident saving amounts to RM134,640 per year. This figure is then compared to the costs of  the treatment which totalled say, RM150,000. Assuming Assuming delay to traffic due Cawangan Jalan, Ibu Pejabat JKR, K.L

This is the same technique as outlined in Chapter 5 and the Net Present Value Value figures can also be calculated for completed  schemes following the example given in that Chapter.. This would be particularly Chapter advisab1e if there are considerable new maintenance costs associated with the installed measure. It is only by evaluating and recording results in this way that a listing of implemented  remedial measures and their effectiveness can be built up for the use of road  authorities throughout the country. country. 7:10.5 Evaluating Overall Effectiveness

This chapter has concentrated on evaluating the effects of specific schemes. In addition there is a need for the regular strategy document mentioned in Chapter I to provide a summary of the overall achievements of  road safety programmes. As background information in the strategy document it is normal to present and  examine aggregate accident statistics over  the State, District or Municipality, broken down in various ways by, for example, Class of road user, class of road. These aggregate figures can be useful not only in indicating general priorities but also in evaluating the effects of wide-scale safety campaigns, legislative and/or enforcement changes. However, as schemes are usua1ly localised, However, their effects are often difficult to detect among much larger accident totals. Hence in the strategy document or Road Safety Plan it will probably be better to give a summary Page 74

 

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listing of the effectiveness of all the low-cost schemes (see Appendix A examples). This is more informative than a single overall figure as it displays the range

of safety efforts taking place and the relative success of the various methods used.

REFERENCES 1.

RADI RADIN N UMA UMAR R R S, S, G M MACK MACKA AY, B L HI HILL LLS. S. Prel Prelim imin inar ary y ana analy lysi siss of of motorcycle accidents:short-term impacts of the running headlights campaign and  regulation in Malaysia.To be published in J.of Traffic Medicine-1995

2.

HAUER E,& P BYER. Bias by selection: the accumcy of an unbiased estimator. estimator. Accid-Anal.& Prevention-15, 5, pp323-328-1983.

3.

ABBESS C, D JARRETT, JARRETT, C C WRIGHT-Accidents WRIGHT-Accidents at blackspots: estimating the effectiveness of remedial treatment,with special reference to the ‘regression to mean’ effect. Traffic Traffic Engineering & Control, 22 22 10-1981.

4.

WRIGHT C C, C R ABBESS & D F JARRETT. JARRETT. Estimating the regression-to-mean effect associated road accident blackspot treatment:- towards approach. Accid. with Anal.& Prevention. 20, 3, pp199-214, 1986. a more realistic

5.

MOUNTAIN L,B FAWAZ & L SINENG. SINENG. The assessment assessme nt of changes in accident accide nt frequencies on link segments: a comparison of four methods.Traffic Engineering & Control, 33, 7 -1992.

6.

BOYLE, A J & C C WRIGHT. WRIGHT. Accident migration after remedial treatment at accident blackspots. Traffic Engineering & Control, 25, 5 -1984.

7.

PERSAUD, B.Migration of accident risk after remedial treatment at accident  blackspots. Traffic Traffic Engineering & Control, 28,1-1987.

8.

MOUN MOUNT TAI AIN N L, & B FA FAWAZ. AZ. T The he eff effec ects ts of of engi engine neer erin ing g meas measur ures es on on safe safety ty at at adjacent sites. Traffic Traffic Engineering & Control, 33, 1-1992

9.

ADAM ADAMS S J. J. Ris Risk k and and fre freed edom om:th :thee reco record rd of roa road d saf safet ety y regu regula lati tion on.. T Tra rans nspo port rt Publishing Projects. Cardiff -1985.

10 10..

TRIM TRIMPO POP P R M, & G J S WILD WILDE E Chal Challe leng nges es to to acci accide dent nt pre preve vent ntio ion: n: the the iss issue ue of  of  risk compensation behaviour. STYX Publications, Postbus 2659, 9704 CR Groningen, The Netherlands -1994.

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CHAPTER VIII SUMMARY Summary Of Chapter Summary Chapter I - INTRODUCTION

Thesummarised main pointsascovered  be follows:in this chapter can 







Road accidents are a serious  problem in Malaysia with more than one person in every 450 of the  population suffering injury or death on the road each year. This Guide focuses on the Engineering aspects of improving safety.

The four basic strategies for reducing accidents are: -Single sites/blackspots -Mass action schemes -Route action plans -Area-wide schemes

Maintenance a reliable accident database is mof essential element of  safety work since it constitutes the  base measure used to: i) identify the nature and location of   problems, and  ii) to monitor the effects of remedial action taken.



The Guide also concentrates on the accident approach (althoughreduction the priciples applied in devising colinsermeasures also be adopted at the design stage in order  to prevent accidents)



Summary Of Chapter Summary Chapter II - ACCIDENT DAT DATABASE

Accident Investigation Units should   be set up in all road authorities with one full-time staff per 400-1000 accidents per year.



The data originates with the Police  but the responsibilities of various authorities are summarised below:-

Balai Police

- Attend scene of accident and record  details - Enter basic details in 24.hour incident report book  - Open investigation file (for all injury and  some damage-only accidents) - Complete POL27 form



The national reduction to targets shouldcasualty be disaggregated the local level, and a planned giving details of how they will be met, and  reporting progress/success. 

An annual Road Safety Plan should   be produced by all road authorities to include a local accident analysis, statement of the targets, giving details of how they will be met, and  reporting progress/success.

Output:

- Main copy of POL27 to HQ - Pages 4 & 15 copies to District JKR/Local Government Office - Investigation papers for court case Police HQ-Bukit Aman

- Receive POL27 forms, check, and enter  onto mainframe computer  - Download Download data to MAAP MAAP files Output:

- Send copy of MAAP files to HPU

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- Single site listing by worst nodes and links, ie. descending order of  accidents.

JKR District Office

- Produce appropriate scale maps marked  with landmarks. - Check POL27 forms for accident location on all State & Federal roads - Fill in Section No, 100m distance, map code, X-Y coordinate coordinate coding. coding.

- Mass action sites can be ranked  according to numbers of accidents of a selected factor (eg. night time accidents) - For Area wide action , residential areas need to be divided into approximately l km squares (though irregular shapes bounded   by rail lines, roads, rivers etc. will ultimately be used).These areas are usually ranked by numbers of  vulnerable road user accidents.

Output:

- Completed pages 4 & 15 of POL27 send to HPU Local Government Department

- Produce appropriate nodal scale maps. - Check POL27 forms for accident location on all Urban principal and minor roads. - Fill in Node, Link Nos, map code, X-Y coordinate coding.

STEP 2: Preliminary Accident Analysis Output:

- Completed pages 4 & 15 of POL27-send to HPU



Test sites in first listing to ensure high accident numbers have not occurred by chance.

Highway Planning Unit (MOW)

- Coordinate all location data - Merge this with data from Police HQ into MAAP computer computer files. files.



Produce stick diagrams to help look  for common patterns of accident.

STEP 3: Initial Initial Site Visit Visit Output:

- Complete data set copy sent to Police HQ - Appropriate data files made available to all authorities.





Summary Of Chapter Summary Chapter III - INVESTIGATION

Step 1: Identifying And Prioritising Sites 







Check plans are up to date. Visualise accidents on record to confirm manoeuvres and make  preliminary judgement of causes. Photograph site. Classify sites if possible as ‘easy’ or  ‘hard’.

Define a reaction level above which action should be taken. Search data ideally covering a  period of 3 years using MAAP to  produce initial ranking of sites. These can be:- Route action listing in descending order of accident totals ( or points)  per Section Number per year.

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Summary Of Chapter Summary Chapter IV - DIAGNOSIS

i) Supplement accident data, ii) Help diagnose diagnose problems, problems, and 

STEP 4 Collection Of Further Data  And Analysis 

iii) Use in future evaluation of remedial work implemented.

Study accident data at the site in more detail including sketch diagrams, and produce collision diagrams.



Classify accidents into types.



Amend stick diagrams to include my further information and search for dominant accident patterns.



Gather any available data such as traffic flow, dates of road  alterations.



Determine likely human factors any perceptual traps.

Summ Summary ary Of Chapter Chapter V - SELECTION

STEP 6 Select Select Posibble Posibble Countermeasures 

A road hierarchy hierarchy should should be estab1ished.



Decide on economic objectives for the different scheme types (eg.50% FYRR at single sites to10-25% area-wide action).



Several treatment proposals(lists for  a site should be considered of schemes shown to be effective in several countries are given), and  each should:-

STEP 5: Site Studies Studies And Analysis Analysis 

Make further site visit and look for  likely features which may be contributing to accidents.

- aim to reduce the prevalent accident type(s);



Plan the following further studies, as necessary:

- not increase other types of accident at the site or in the surrounding area;

- Traffic flow manoeuvre counts. - Pedestrian road crossing flow in marked  road lengths if relevant.

- not cause undesirable effects on other  traffic movements or on the environment. 

For area-wide residential schemes, aim to reduce speeds as opposed to restricting vehicle movements and  maintain good consultation with locals and the emergency services.



Consider whether schemes need to incorporate road user training and  media campaigns.

- Speed measurements on approach to  junctions or bends indication of possible  problems. - Take still photographs and/or video as a record for report, or use to study problem  behaviour..  behaviour - Conduct traffic conflict study most useful at junctions to :

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STEP 7: Priortise Treatments Treatments & Sites 



Estimate costs and benefits of each treatment for which the following is required:

Monitoring should be carried out at different levels: for the whole area covered by the road authority; immediately after each individual scheme; and for longer term conclusions.

- capital costs - estimate of benefits - estimate of any disbenefits. 



Select most cost-effective solution in terms of best First Year Year Rate of  Return (FYRR) or best Net Present Value to Present Value Cost ratio (NPV/PVC). Only those schemes with FYRR > 50% should initially  be considered.





Draw up list of sites in priority order of best NPV/PVC ratio, and  decide on cut-off of sites to be

Variables other than accident frequency can be used to monitor  the effectiveness, particularly in relation to the objectives of the  particular countermeasure. A series of other factors are strongly recommended for area-wide schemes. It is important to monitor other  surrounding areas which could be affected by the scheme and to identify as large a group of control sites as possible of similar nature  but well away from the study sites.

treated within the budget. Summary Of Chapter Summary Chapter VI - IMPLEMENTATION

STEP 8: Detailed Detailed Design Design And   Installation 



Carry out a road safety audit at the design stage and immediately before opening to traffic.

Remedial action schemes should be evaluated so that knowledge can be gained  about relative performances. This will assist decision making on efficient allocation of  resources in the future. 

Statistical tests should be used in  before and after studies to compare accident changes at the treated sites with the control sites.



The investigator should make allowance for the known other  factors that can affect the estimate of the effect of the measure on accidents (eg. regression-to-mean).



As a guide to overall effectiveness of a road authority’s road safety  programme, a summary list of  individual schemes, grouped in an appropriate manner, should be  produced and included in the Road  Safety Plan document.

Ensure adequate safety standards are followed at the safety improvement construction site.



STEP 10: Evalu Evaluation ation

Maintain a 1og of dates of the works and of actual costs.

Summary Of Chapter Summary Chapter VII - EVALUATION

STEP 9: Monito Monitoring ring

The importance of monitoring after scheme implementation is stressed   .

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APPENDIX A Exampl Exa mple e of Ro Road ad Safety Safety P Plan lans s This Appendix contains extracts from recent road safety strategy documents or Road Safety Plans of two highway authorities authorities in the United Kingdom, ie. Doncaster Metropolitan Borough Council and Berkshire County Council. They are included as examples only of the format anddocuments type of information which, it is recommended, be incorporated in similar   published in Malaysia. Road Safety Plans are now produced annually by most road authorities in the United  Kingdom regardless of the current success or failure of each in achieving its target. They serve as a means of ensuring that the road authority concentrates on managing its particular   problems effectively, effectively, and provide the public and higher authorities with a valuable record of  the efforts it is making on their behalf towards improving the safety of the road network. It should be noted that Berkshire County Council, having responsibility for a larger road  network, have now appointed a commercial highways and planning consultants, the Babtie Group, to carry out the task of producing their Plan.

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2.0 PROGRESS TOWARDS TARGET Berkshire Progress

In 1989 when the County Council Council adopted the casualty reduction target, some some 4354 casualties had resulted from accidents on Berkshire’s roads. In order to achieve the target reduction of one third of the average 1981-85 figure by the year 2000, this figure must reduced to 2847. Progress towards the target is shown opposite. Whilst casualty numbers continue to decline it can be seen that an increased rate of reduction is now required if the objective is to be achieved. National Progress

For comparison purpose the national progress towards the year 2000 target is also shown opposite. It can be seen performance in Berkshire is better than the national average. It can be seen that both the Berkshire and National trends show the same effect: an early and  relatively rapid reduction as the “easier” sites are tackled, followed by a levelling off as more difficult problems (often related to behaviour as much as to the road layout) have to be tackled.

WHILST CASUALTY NUMBERS NUMBERS CONTINUE TO DECL DECLINE, INE, MORE SIGNIFICANT   REDUCTIONS ARE REQUIRED TO MEET THE YEAR 2000 TARGET 

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3.0 ACCIDENT TRENDS AND ANALYSIS An analysis of accident trends has shown that speeding particularly in urban areas continues to be a major factor in accident causation. The young and inexperienced road users feature  predominantly in Berkshire's accident statistics, and the fact that two-thirds of all casualties resulting from accidents on Berkshire's roads are the drivers and passengers of cars is a cause for concern. It is at these key areas that resources must be targeted if the year 2000 targets is to be met. The Size Of The Problem

Throughout 1993 on roads in Berkshire there was a total of 2773 accidents involving  personal injury. injury. These resulted in 3672 casualties of which: 33 347 292

were fatal were sseerious in injuries 3 were slight injuries

The total number of fatalities and serious injuries has declined every year since 1989 and  now represents a 65% reduction over the 1981 - 85 average figure.

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The only specific road user group showing and increasing casualties trend is that of car  occupants. Casualty levels in this group are currently 10% higher than the 1981-85 average. It is clear that this casualty group holds the key to achieving the casualty reduction target and the County Council's objective in the next few years will be to reduce casualties in this area.

THE KEY TO TO ACHIEVING ACHIEVING THE YEAR 2000 TARGET TARGET WILL BE REDUCE T TO O REDUCE  CASUALITIES IN THE CAR OCCUPANT ROAD USER GROUP Cawangan Jalan, Ibu Pejabat JKR, K.L

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Accidents Locatios In Berkshire

As can be seen in the figures below, the majority of accidents in Berkshire take place on urban roads. (i.e. those roads subject to a speed limit of 40mph or less). It is evident that if  the casualty reduction target is to be met then a significant proportion of engineering  programmes and police enforcement activity must be focused on these areas .

THE COUNTY COUNTY COUNCIL COUNCIL WILL CONTINUE TO FOCUS FOCUS ROAD SAFETY RESOU RESOURCES  RCES  TOWARDS TOW ARDS ACCIDENT CONCENTRATIONS, CONCENTRATIONS, PARTICULARLY PARTICULARLY THOSE IN URBAN AREAS 

Vulnerable Road User Groups In Berkshire Berkshire

The distribution of road traffic casualties by age and road user class shows that inexperienced users of each mode are more likely to be involved in accidents. This is  particularly evident with the young car driver since accident records show that over  one-third of all accidents involve drivers in the 17 to 24 age range.

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As discussed in later sections, Education Training and Publicity initiatives are directed   principally at these inexperienced and hence vulnerable groups. Speed

Speeding by drivers and riders is the most common contributory factor to deaths and injuries on Berkshire's roads. A study by the Transport Transport Research Laboratory (TRL) (TRL) has indicated that between 22 and 32  percent of the accidents studied had excessive speed as a contributory factor. In terms of the 1993 injury road accident figures for Berkshire, this would indicate that speeding had been involved in over 800 injury road accidents. As discussed in later sections, the theme of excessive speed and road safety will play a major part in the County Council's engineering and education programmes and in the enforcement activity of Thames Valley Valley Police.

 AN ANALYSIS BY TRL INDICATES INDICATES THAT A REDUCTION IN   AVERAGE  AVERAG E SPEED EVERYWHERE OF THE ORDER OF 1 KPH COULD SAVE SAVE 5 PERCENT PERCE NT OF ALL INJUR INJURY YA ACCID CCIDENTS  ENTS 

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4.0 ENGINEERING ACTION The great majority of schemes in the County Council's highway works programme will result in road safety improvements. Indeed the Council's scheme selection procedures are heavily biased towards tackling sites with a persistent injury accident problem. In recognising the importance of reducing the level of accidents on the County's roads the Government allows Supplementary Credit Approval (SCA) to be claimed against engineering projects which can demonstrate potential injury accident savings. Hence it is in the County's interest to promote such schemes above those to which no potential injury accident savings can be ascribed. Recent engineering road safety initiatives are listed below:



TRAFFIC CALMING has continued to be heavily promoted within Berkshire with numerous projects including 20mph zones, chicanes, road narrowings, road humps and mini roundabouts being installed around the County.



In recognition of the accidents caused through excessive speed by drivers and riders in urban areas, Berkshire County Council quickly responded to the regulations issued in 1992 by installing the first 22 fixed speed camera sites in Berkshire. This work will continue in 1994/95 with a further 50 sites planned and complements red  light enforcement cameras already installed.



The first non-trunk road variable speed limit scheme in the country was introduced  in Slough.



The first Berkshire Toucan crossing is being progressed in Newbury.

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Berkshire’ss 3rd Puffin crossing is being progressed in Thatcham. Berkshire’

Appendix A lists local safety engineering schemes planned for 1994/95 together with comment on their estimated effect on injury accidents over a three year period. As can  be seen considerable emphasis will continue to be placed on tackling the problems of  speeding in urban area with many speed camera and traffic calming schemes programmed at identified measures high risk accident schemes are seen as one theexpected prime accident reduction currentlysites. beingSuch implemented in Berkshire andofare to make a major contribution towards changing attitudes to inappropriate speeds. The County Council carries out a continuous programme of investigation of accident  patterns at High Risk Sites. Potential schemes arising from this process are presented to Members for funding consideration The potential for reducing accidents will continue to be taken into account when deciding on the priorities for traffic management works promoted by the Area Highway Sections. Appendix B lists all High Risk sites in Berkshire with comment on action already taken or   proposed.

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A minimum of 100 sites will be investigated in depth depth in 1994/95 either as individual sites or  as part of an area wide or route approach. In addition to this, accident investigation will continue to feature predominantly in the County Council's continuing programme of Area Traffic and Transport Studies. The County Council continues to monitor its success in accident remedial work to ensure a cost effective approach to the work. Indeed, this feedback is essential to maintain levels of  expertise in this rapidly developing field. Appendix C gives before and after information and  clearly demonstrates the cost effectiveness of this work. The County Council continues to improve road safety through its close control of  development proposals and liaison with the local Planning Authorities. Every opportunity will be taken to resolve existing road safety problems or prevent others arising as a result of  new development. Developer contributions will also be actively sought to enable positive accident prevention and remedial work to be pursued at identified problem sites.

CONSIDERABLE EMPHASIS EMPHASIS WILL CONTINUE TO TO BE  PLACED ON TACKLING THE PROBLEM OF SPEEDING IN VRBANAREAS AT   IDENTIFIED HIGH RISKACCIDENT RISKACCIDENT SITE S. S.

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APPENDIX B POL27 Accident Accident Report Form

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APPENDIX C Poisson Probabilities (Single Factor Values)

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APPENDIX D Chi-squared Table

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APPENDIX E Standard Symbol For Collision Diagrams

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APPENDIX F Discount Factor Tables

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APPENDIX G Comparison Compa rison Of Mean Speed Measu Measurr emen ements ts and and T-Distribution Table COMPARISON OF MEAN SPEED

Having found the value of  t we look at

MEASUREMENTS To determine whether the mean speed  of one set of speed measurements is significantly different from another (ie.between a “before” and “after” study), it is necessary to determine the means and  standard deviation of the difference in means.

 b- 2) degrees the table over with of (n ta+n of freedom. If page the value exceeds that for  the 5% level (the  t =0.05column) we can be 95% conndent that the true mean speed has changed.

Let b1,b2..................bnb the before speed  readings and a1,a2,..............ana be the after speed  readings we then ca1culate the equations below:

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