AP-R519-16 Guidance on Median and Centreline Treatments to Reduce Head-On Casualties

Research Report AP-519-16

Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Guidance on Median and Centreline Treatments to Reduce Head-on Casualties Prepared by

Publisher

David Beck

Austroads Ltd. Level 9, 287 Elizabeth Street Sydney NSW 2000 Australia Phone: +61 2 8265 3300 [email protected] www.austroads.com.au

Project Manager Alex Duerden Abstract

About Austroads

This report presents a compendium of local and overseas practice and experience in minimising the risk and severity of head-on crashes. It is intended to assist road safety practitioners identify effective actions that can be taken to reduce the incidence and severity of such crashes, with a focus on median and centreline treatments.

Austroads is the peak organisation of Australasian road transport and traffic agencies.

In addition to discussing well-proven methods to address head-on crashes, this report also presents some innovative treatments for which there is currently insufficient data to confirm their benefits, but which may be effective in reducing head-on crashes where the crash history does not justify the expense of applying more established treatments.

Austroads’ purpose is to support our member organisations to deliver an improved Australasian road transport network. To succeed in this task, we undertake leading-edge road and transport research which underpins our input to policy development and published guidance on the design, construction and management of the road network and its associated infrastructure. Austroads provides a collective approach that delivers value for money, encourages shared knowledge and drives consistency for road users. Austroads is governed by a Board consisting of senior executive representatives from each of its eleven member organisations:

Keywords Head-on crash, centreline treatment, median treatment, road safety

ISBN 978-1-925451-13-9 Austroads Project No. SS1959 Austroads Publication No. AP-R519-16 Publication date June 2016 Pages 72 © Austroads 2016

    

Roads and Maritime Services New South Wales

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Department of State Growth Tasmania

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Australian Government Department of Infrastructure and Regional

 

Australian Local Government Association

Roads Corporation Victoria Department of Transport and Main Roads Queensland Main Roads Western Australia Department of Planning, Transport and Infrastructure South Australia Department of Transport Northern Territory Territory and Municipal Services Directorate, Australian Capital Territory

New Zealand Transport Agency.

This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without the prior written permission of Austroads. This report has been prepared for Austroads as part of its work to promote improved Australian and New Zealand transport outcomes by providing expert technical input on road and road transport issues. Individual road agencies will determine their response to this report following consideration of their legislative or administrative arrangements, available funding, as well as local circumstances and priorities. Austroads believes this publication to be correct at the time of printing and does not accept responsibility for any consequences arising from the use of information herein. Readers should rely on their own skill and judgement to apply information to particular issues.

Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Summary This report presents a compendium of local and overseas practice and experience in minimising the risk and severity of head-on crashes. It is intended to assist road safety practitioners identify effective actions that can be taken to reduce the incidence and severity of such crashes, with a focus on median and centreline treatments. While the body discusses road engineering measures that address the safe roads and speeds pillars of the Safe System framework, some details on methods to address the safe vehicles and road users pillars are included in Appendix B. In addition to discussing well-proven methods to address head-on crashes, this report also presents some innovative treatments for which there is currently insufficient data to confirm their benefits. Nonetheless, these methods are expected to be effective in reducing head-on crashes, and may be of benefit in situations where the site crash history does not justify the expense associated with more established treatments. Opportunities for further research to confirm benefits of specific treatments have been highlighted. Appendix A presents an at-a-glance overview of the road engineering based treatments discussed earlier in this report, including crash modification factors, indicative costs and typical characteristics that may inform the decision to adopt this treatment. Where information has yet to be obtained or is limited, the table also identifies areas of research that could benefit our understanding of road safety solutions. As with all Austroads guidance documents, this report serves to present an overview of the available treatment options only. The reader is advised to consult with the relevant local jurisdiction for the crash modification factors, costs and treatment lives used for local cost-benefit analysis methods, as well as any specific policies or design specifications pertaining to this treatment for that jurisdiction. The reader is also advised to consult with the manufacturer for any product-specific requirements.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Contents 1.

Introduction ............................................................................................................................................ 1 1.1 Background ...................................................................................................................................... 1 1.2 Key Contributing Factors .................................................................................................................. 1 1.3 Intent of the Report ........................................................................................................................... 2 1.4 Structure of this Report .................................................................................................................... 3 1.5 Crash Modification and Reduction Factors ...................................................................................... 3 1.6 Approved Safety Barrier Products .................................................................................................... 4

2.

Centreline Treatments ........................................................................................................................... 5 2.1 Standard Dividing Linemarkings ...................................................................................................... 5 2.2 Raised Profile Centrelines ................................................................................................................ 7 2.3 Raised Profile Centrelines and Edgelines ...................................................................................... 10 2.4 Enhanced Pavement Markings ...................................................................................................... 11 2.5 Raised Reflective Pavement Markers ............................................................................................ 13 2.6 Internally Illuminated Pavement Markers ....................................................................................... 14

3.

Median Treatments .............................................................................................................................. 16 3.1 Painted Median .............................................................................................................................. 16 3.2 Pavement Bars ............................................................................................................................... 18 3.3 Wide Centreline Treatment ............................................................................................................ 19 3.4 Raised Median ............................................................................................................................... 22 3.5 Barrier Kerbing on Median ............................................................................................................. 24 3.6 Median Barriers .............................................................................................................................. 25 3.6.1

Rigid Median Barriers ........................................................................................................ 27

3.6.2

Semi-rigid Median Barriers ................................................................................................ 29

3.6.3

Wire Rope Median Safety Barriers .................................................................................... 30

3.6.4

2+1 Roads ......................................................................................................................... 33

3.6.5

Moveable Barriers ............................................................................................................. 35

3.6.6

Motorcyclist Concerns with Median Barriers ..................................................................... 36

3.6.7

Median Barrier Terminal Treatments................................................................................. 37

3.7 Flexible Bollards ............................................................................................................................. 37 3.8 Median Turning Bays ..................................................................................................................... 39 3.9 Median Design ............................................................................................................................... 40 3.9.1

Median Width..................................................................................................................... 40

3.9.2

Cross-section..................................................................................................................... 41

3.9.3

Pavement Edge Drop-off ................................................................................................... 41

3.9.4

Median Shoulder ............................................................................................................... 42

3.10 Median Glare Treatments............................................................................................................... 44 3.11 Median Plantations ......................................................................................................................... 45 4.

Other Road Infrastructure Solutions ................................................................................................. 47 4.1 Speed Management ....................................................................................................................... 47 4.2 Intermittent Overtaking Lanes ........................................................................................................ 47 4.3 Improved Pavement Surface .......................................................................................................... 49 4.4 Shoulder Treatments ...................................................................................................................... 49

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

4.5 Improved Roadside Forgiveness ................................................................................................... 50 4.6 Curve Delineation and Warning ..................................................................................................... 50 4.7 Addressing Wrong-way Movements .............................................................................................. 52 5.

Conclusion ............................................................................................................................................ 55

References ................................................................................................................................................... 56 Summary of Treatments ................................................................................................. 63 Other Countermeasures to Address Head-on Crashes............................................... 68

Tables Table 2.1: Table 2.2: Table 3.1: Table 3.2: Table 3.3: Table 3.4: Table 3.5: Table 3.6: Table 4.1:

Summary of CRFs and CMFs (bracketed) sourced from various references for raised profile centrelines ........................................................................................................................... 9 Summary of crash reduction and modification (bracketed) factors for application of raised profile centrelines and edgelines .................................................................................................11 FSI crash ratio for safety barrier solutions ...................................................................................27 Summary of crash reduction and modification (bracketed) factors for WRMB treatment of head-on, single-vehicle and FSI crashes extracted from selected studies ..............................32 Crash modification factors for crashes of varying severity extracted from selected studies .......32 Crash modification factors for full-access controlled medians based on width ...........................40 Crash modification factors for partial-access controlled or no-access medians based on width ........................................................................................................................................41 CMFs for varying the median shoulder width on freeways ..........................................................43 Summary of various curve delineation treatments and respective crash reduction and modification factors ......................................................................................................................52

Figures Figure 2.1: Figure 2.2: Figure 2.3: Figure 2.4: Figure 2.5: Figure 2.6: Figure 2.7: Figure 2.8: Figure 2.9: Figure 3.1: Figure 3.2: Figure 3.3: Figure 3.4: Figure 3.5: Figure 3.6: Figure 3.7: Figure 3.8: Figure 3.9: Figure 3.10: Figure 3.11: Figure 3.12: Figure 3.13: Figure 3.14: Figure 3.16:

Examples of standard dividing linemarkings .................................................................................. 5 Close view of raised profile linemarking ......................................................................................... 7 Example of raised profile centreline ............................................................................................... 8 Raised profile centreline and edgeline treatment.........................................................................10 Installation of road marking tape ..................................................................................................12 Centreline RRPMs during daylight ...............................................................................................13 Centreline RRPMs illuminated at night-time by headlights ..........................................................13 Close view of solar-powered centreline IIPM ...............................................................................14 IIPMs illuminating over a long distance ........................................................................................15 Painted median on curve .............................................................................................................16 Painted median on straight section ..............................................................................................16 Typical layout of painted median..................................................................................................17 Example of pavement bars in median ..........................................................................................18 Examples of wide centreline treatments ......................................................................................19 Layout of painted median outline with raised profile linemarking ................................................20 Wide centrelines highlighted by RRPMs and coloured linemarkings respectively ......................20 Example of wide centreline designed to allow for overtaking for both flows of traffic and one flow of traffic respectively ...............................................................................................21 Paved raised median ...................................................................................................................22 Grassed raised median providing shelter for signs and lighting ..................................................22 Drivers using raised median as transit lane on congested road ..................................................23 Example of median barrier kerbing ..............................................................................................24 Further example of median barrier kerbing ..................................................................................24 Deflection of errant vehicle by wire rope median barrier .............................................................26 Linear delineation of concrete barrier on a curve.........................................................................28

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Figure 3.17: Figure 3.18: Figure 3.19: Figure 3.20: Figure 3.21: Figure 3.22: Figure 3.23: Figure 3.24: Figure 3.25: Figure 3.26: Figure 3.27: Figure 3.28: Figure 3.29: Figure 3.30: Figure 3.31: Figure 3.32: Figure 3.33: Figure 4.1: Figure 4.2: Figure 4.3: Figure 4.4: Figure 4.5:

W-beam barrier along wide median .............................................................................................29 W-beam barrier along narrow median .........................................................................................29 WRMB in wide centreline .............................................................................................................30 Overlapping of WRMB systems ...................................................................................................31 Typical 2+1 road configuration .....................................................................................................33 2+1 roadway.................................................................................................................................34 Typical 2+1 road cross-section ....................................................................................................34 Images of moveable barrier being transitioned, including over Auckland Harbour Bridge ..........35 Examples of motorcycle barrier post protection systems ............................................................37 Flexible bollards on motorway......................................................................................................38 Flexible bollards that may later be replaced with WRMB ............................................................38 Diagram of operation of median turning bays ..............................................................................39 Example of median turning bay....................................................................................................39 Examples of uneven pavement edge drop-off .............................................................................42 Example of paved median shoulder on highway .........................................................................43 Antiglare screens .........................................................................................................................44 Median plantation .........................................................................................................................45 Roadway featuring intermittent overtaking lanes .........................................................................48 Delineation of curve with CAMs ...................................................................................................51 Delineation and warning of curve with vehicle activated signage and chevron board .................51 ‘Drive on left in Australia’ signage used in the Barossa Valley ....................................................53 Wrong way/go back signage at motorway exit (inset shows greater detail) ................................54

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

1. Introduction 1.1

Background

The Safe System approach to road safety has been adopted in Australia and New Zealand. This approach aims to provide a road system that protects compliant road users from death and serious injury. A Safe System approach also recognises that road users are fallible and will continue to make mistakes, but that they should not be penalised with death or serious injury when they do. Part 1 of the Austroads Guide to road safety (Austroads 2013) discusses the Safe System approach in detail. In part, the Safe System approach requires (Australian Transport Council 2011):

 Designing, constructing, and maintaining a road system (roads, vehicles and operating requirements) so that forces on the human body generated in crashes are generally less than those resulting in fatal or debilitating injury.

 Improving roads and roadsides to reduce the risk of crashes and minimise harm. Measures for higher speed roads include:

– segregating traffic – providing and maintaining ‘forgiving’ roadsides – providing clear driver guidance.  Managing speeds, taking into account the risks on different parts of the road system. In areas with large numbers of vulnerable road users or substantial collision risk, speed management supplemented by road and roadside treatments is a key strategy for limiting crashes. The term ‘head-on crash’ refers to an event in which a vehicle departs from its laneway into opposing traffic, such that any portion of the leading edge of its vehicle strikes any portion of the leading edge of an opposing vehicle. This is one of the most severe crash types that may occur. It is therefore important within a Safe System that practitioners are aware of measures available to reduce the incidence and severity of this crash type. In an average year, there are about 74 fatal head-on crashes in urban environments and 264 in rural environments in Australia and New Zealand combined (Austroads 2014a; Austroads 2010a). Head-on crashes in rural areas are generally high-speed crashes that result in serious injury outcomes. Whilst new vehicles are designed and tested to ensure head-on collisions are survivable at speeds of up to 70 km/h, in real life scenarios, the combined relative speeds in a rural crash can exceed 200 km/h. In interactions between light and heavy vehicles, much of the impact energy from this relative speed will be transferred to the light vehicle. The high severity of this crash type is demonstrated by their high fatality rate – 19% of head-on crashes occurring on rural roads in Australia and New Zealand result in a fatality (Austroads 2010a).

1.2

Key Contributing Factors

A high proportion of head-on crashes occurs on or near curves, when a vehicle crosses the centreline of the road to collide with an oncoming vehicle or object located on the edge of the carriageway. This is an issue particularly when the operating speed is higher than the design speed for a curve, requiring drivers to reduce their speed. Complex curves, featuring more than one curve in close proximity, are also overrepresented at head-on crash sites. Centreline encroachments on left curves are generally a result of excessive speeds or avoidance of roadside hazards, whilst on right curves encroachments are generally due to drivers ‘cutting the corner’ or ‘straightening on the curve’ if they consider it safe to do so (Austroads 2010a; Austroads 2014a). A high proportion of head-on crashes on rural roads occur in wet conditions (19% in Australia and 29% in New Zealand).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

On rural roads, the following road design characteristics have been identified as common features of sites with high head-on crash rates (Austroads 2010a):

     

poor sight distance for overtaking due to horizontal and vertical curves unsealed or partially sealed shoulders inappropriate speed limits poor curve delineation insufficient or unclear advisory/warning signs, such as for curves, advisory speeds, intersections, etc. insufficient or poorly maintained raised reflective pavements markers (RRPMs) delineating the road and vehicle lanes.

On urban roads, the following road design characteristics have been identified as common features of sites with high head-on crash rates (Austroads 2014a):

 steep downhill gradients leading into curves  limited sight distance both at intersections (signalised and unsignalised) and mid-block  presence of visually imposing or unforgiving roadside furniture that may encourage drivers to travel further from the road edge, reducing the buffer from opposing traffic.

 Poor coordination of horizontal and vertical alignments are also a key contributing factor to vehicle lossof-control, which can result in head-on crashes (Austroads 2015a). Heavy vehicles are involved in a notable proportion of rural head-on crashes (17% in Australia and 10% in New Zealand). Head-on crashes are the second most common crash type for heavy vehicles on rural roads in Australia, and the most common crash type for heavy vehicles on rural roads in New Zealand (Austroads 2009c). These crashes result in more severe outcomes, with 28% of such crashes on rural roads resulting in a fatality, compared to 19% for all rural head-on crashes (Austroads 2010a).

1.3

Intent of the Report

This report presents a compendium of local and overseas practice and experience in minimising the risk and severity of head-on crashes. It is intended to provide guidance to practitioners on effective actions that can be taken to reduce the incidence and severity of head-on crashes, with a focus on road engineering measures, particularly median and centreline treatments. Median and centreline treatments are generally effective by providing:

   

a visual separation of vehicles (e.g. centreline markings) a kinetic deterrent to vehicles crossing the median (e.g. raised profile linemarkings) a physical deterrent to discourage vehicles from crossing the median (e.g. raised median) a physical obstruction to prevent vehicles crossing the median (e.g. median barriers).

Some of the treatments discussed will also assist in reducing other crash types, and so application of these treatments can have additional benefits to their ability to address head-on crashes. Alternately, some treatments, whilst addressing head-on crashes, may create other unintended road safety issues. The practitioner is advised to carefully consider what implications, whether positive or negative, a particular treatment may have. The reader is advised to consult with the relevant local jurisdiction for specific details relating to a treatment, such as crash modification factors, costs and treatment lives used for local cost-benefit analysis methods, as well as any specific policies or design specifications pertaining to this treatment for that jurisdiction. The reader is also advised to consult with the supplier for any product-specific requirements.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

1.4

Structure of this Report

The report is comprised of six sections, as follows:

 Section 1 (this section) presents the background to the Austroads project and outlines the scope and intent of the report.

 Section 2 presents local and international experience in using centreline treatments to address the incidence and severity of head-on crashes.

 Section 3 presents local and international experience in using median treatments to address the incidence and severity of head-on crashes.

 Section 4 discusses other road engineering based countermeasures to address head-on crashes, included speed-based treatments.

 Section 5 provides the concluding comments, including the key findings and limitations of the research, as well as identification of areas for future study in the area of treating head-on crashes. An at-a-glance overview of all centreline, median and other road engineering based countermeasures is included in Appendix A. This section also includes indicative costs for treatments. As can be seen, many of these costs vary significantly between jurisdictions. Costs are a guide only to assist in comparing treatments. Practitioners are advised to consult with their local jurisdiction for more accurate cost estimates when preparing a cost-benefit analysis. Costs may vary based on the jurisdiction, project scope, site location and other environmental factors. Having considered road and speed-based treatments in the report, Appendix B has been included to consider the other pillars of the Safe System, namely vehicle and behavioural based countermeasures. Whilst these are not road-based treatments, and therefore not included in the main body of the report, it is important for road safety practitioners to be aware of other solutions available within the Safe System.

1.5

Crash Modification and Reduction Factors

In discussing treatments, this report aims to identify the respective crash modification and reduction factors. According to the Austroads Glossary of Terms (Austroads 2015b):

 The crash modification factor (CMF) is a ‘representation of the relative change in crash frequency that occurs due to a specific change in the road or its immediate environments’.

 The crash reduction factor (CRF) is an ‘indication of the expected percentage reduction in road crashes following the introduction of a countermeasure’. To illustrate, a CRF of 60% would suggest that 40% of crashes would remain. The CMF would therefore be represented as 0.4. A treatment with a negligible CRF would have a CMF of 1.0, indicating that the same crash rate would remain after application of the treatment. A negative CRF of –20% indicates a 20% increase in crashes, so would be indicated as a CMF of 1.2. CRFs and CMFs are general indications only, and may vary due to a range of factors. All values presented in this report have been rounded to the nearest 5%. Presenting factors with greater accuracy would potentially mislead the reader as to the accuracy of the research and its applicability to individual scenarios. These values have been presented as a guide only, and practitioners should consult their local jurisdictions for pertinent CMF values when preparing cost-benefit analyses. Section 4.6 of the Austroads Guide to road safety (Austroads 2015c) provides guidance on how to determine the CRFs for applying multiple treatments at one site. Most research reviewed for this project reported only the crash reductions for all crash types combined, and did not consider reductions for head-on crashes explicitly. Where crash reductions are for head-on crashes in particular, this has been indicated.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

1.6

Approved Safety Barrier Products

Safety barrier products referenced in this publication are included as examples of treatments used in different road environments and countries. Contact your local road agency for products approved for use in your jurisdiction.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

2. Centreline Treatments 2.1

Standard Dividing Linemarkings

Delineation is designed to visually guide drivers safely along the roadway by influencing their choice of position and speed. When delineation is lacking or inadequate, the driving task becomes more difficult, and drivers have a greater chance of leaving their travel lane. If the lane departure is to the right, the nominal centreline of the road is crossed and a head-on crash may occur. Drivers may also decide to conduct an overtaking manoeuvre (either permissible or illegal), which on two-lane roads will require all or part of the vehicle crossing into the opposing lane. The Australian Standard, AS 1742.2-2009 covers the design of centreline markings (referred to as dividing lines) for use in Australia1. The markings may comprise a: 1. double two-way line, consisting of two continuous lines side by side, indicating that crossing of the line is prohibited for both travel directions 2. double one-way barrier line, featuring a continuous line beside a broken line, indicating that crossing of the line is permitted only for traffic travelling on the left of the broken line 3. single barrier line, featuring a single continuous line, indicating that no overtaking is permitted, but crossing by traffic entering or leaving the roadway is permitted 4. dividing line, featuring a single broken line, serving to separate traffic, but allowing crossing of the line for traffic travelling in either direction. Figure 2.1 shows examples of each dividing linemarking. These linemarkings and the associated rules are referenced in the Australian Road Rules and the New Zealand Road Code. Legislation in all jurisdictions in the two countries requires compliance with these rules, which are enforceable by the police and which may have a bearing on the outcome of civil actions. In many jurisdictions, emerging road regulations allow vehicles to cross the centreline, where it is safe to do so, to enable a minimum 1 metre passing distance (clearance) to cyclists. The safety impact of this recent development will need to be monitored over time. Dividing lines are not generally used on sealed roads of less than 5.5 m width, given that in practice the drivers of most cars and larger vehicles would have no choice but to straddle the centreline. Figure 2.1:

Examples of standard dividing linemarkings

(a) Double two-way line

1

(b) Double one-way barrier line

Each jurisdiction is likely to provide their own policy on how to apply AS 1742.2-2009 locally.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

(c) Single barrier line

(d) Dividing line

Source: ARRB Group.

When the traffic volume is very low, e.g. under 300 vehicles per day (vpd) on rural roads, and under 2500 vpd on urban roads, dividing lines may be omitted. Dividing lines are also recommended for use under the following conditions (AS 1742.2-2009):

       

frequent horizontal or vertical curves substandard curves areas subject to fog minor road approaches to intersections with ‘STOP’ or ‘Give Way’ signs curves or crests in residential streets where crash records suggest a need to help ensure continuity of an arterial road where there are significant volumes of night-time or tourist traffic.

Lines used within the central third of the road are generally preferred to be 100 mm wide, though may be as narrow as 80 mm (AS 1742.2-2009). The wider the linemarkings, and the greater the distance between double linemarkings (known as the separation), the greater the separation between vehicles. Double linemarkings with wide separations can be used as a distinct treatment, known as the wide centreline treatment, discussed in Section 3.3 (Austroads 2010e).

Crash modification The New South Wales Roads and Maritime Services (Roads and Maritime) (2015b) suggests a 15% reduction in head-on crashes (CMF of 0.85) for the installation of barrier lines (i.e. both providing delineation and barring overtaking). Austroads (2010d) indicates that centrelines can reduce total crashes on a road by 30% (CMF of 0.70). By preventing overtaking as well as, barrier lines and double two-way lines have a higher crash reduction of 35% (CMF of 0.65).

Treatment life Austroads (2010f) suggests a treatment life of three years can be applied for standard linemarking systems. However, the precise rate of wear at a location is unknown and can be accelerated at certain locations by traffic, roadside activities, weather and other factors.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

2.2

Raised Profile Centrelines

Raised profile centrelines (also known as audible centrelines, audio-tactile centrelines or centreline rumble strips) are raised or grooved patterns placed on or near the roadway centreline. Other audible centrelines can be achieved using grooved patterns on or near the centreline. Figure 2.2 shows a close-up view of the raised profile linemarking, whilst Figure 2.3 shows raised profile linemarking located along a centreline. Such features alert drivers when their wheels reach the centreline by emitting a humming sound and vibrations that are clearly distinguishable from the normal driving experience. As they alert drivers when their vehicle strays towards opposing traffic, raised profile centrelines are most effective at addressing crashes related to driver inattention, distraction or drowsiness (Bahar, Wales & Longtin-Nobel 2001). Figure 2.2:

Close view of raised profile linemarking

Source: AllState LineMarking Australia (n.d.).

As well as providing a clearly audible signal, centreline rumble strips improve visibility of the centreline (especially in wet conditions) and discourage drivers illegally crossing the centreline, such as for overtaking (Torbic et al. 2009; Neuman et al. 2003). Raised profile centrelines may be installed without any changes to the roadway cross-section, thereby serving as a relatively fast and low-cost measure (Neuman et al. 2003). They have been found to be traversable by motorcyclists without causing loss-of-stability (Jamieson et al. 2013). The literature reviewed has determined potential operational issues with raised profile centrelines. The implications of these concerns will need to be considered on a case-by-case basis:

   

additional maintenance requirements (Neuman et al. 2003) high noise levels (Neuman et al. 2003) potential for water ponding if not adequately drained (Bahar, Wales & Longtin-Nobel 2001) potential for presenting a visual obstruction to overtaking manoeuvres (Neuman et al. 2003).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Figure 2.3:

Example of raised profile centreline

Source: ARRB Group.

Practitioners are advised to consider cyclist movements when installing raised profile centrelines since the treatment may encourage drivers to travel closer to the shoulder, reducing the lateral distance between vehicles and any cyclists travelling on or close to the shoulder (Neuman et al. 2003; Kar & Weeks 2009). To mitigate the noise levels associated with this treatment, whilst still ensuring an appropriate audible signal to the driver, Torbic et al. (2009) recommend a lower sound level in built-up areas, of 6–12 dBA in the occupant compartment, compared to 10–15 dBA away from residential areas. Noise levels vary depending on the design of the rumble strips. Practitioners should check with the manufacturer to confirm that noise levels are appropriate for the particular road design.

Crash modification Table 2.1 summarises a number of CRFs and CMFs for the installation of raised profile centrelines, sourced from various references. As can be seen, this treatment type both reduces the incidence and severity of head-on crashes. It is suggested that the severity of head-on crashes is reduced as drivers are alerted to undertake a degree of emergency braking and/or steering with the effect of reducing the impact speed and the extent of the impact area. In addition to the information provided in Table 2.1, Hirasawa et al. (2006) found that raised profile centrelines reduced head-on crashes by 55%, fatalities by 70%, serious injuries by 30% and minor injuries by 25% (CMFs of 0.45, 0.30, 0.70 and 0.75 respectively). These results indicate a greater success at reducing fatal crashes compared to reducing FSI crashes as presented in Table 2.1.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Table 2.1:

Summary of CRFs and CMFs (bracketed) sourced from various references for raised profile centrelines Environment

Head-on (all)

FSI(1) head-on

All crashes

All FSI crashes

Range from all studies below

–

20–55% (0.45–0.80)

25–65% (0.35–0.75)

9–15% (0.85–0..91)

10–30% (0.70–0.90)

Austroads (2010d)

–

–

–

15% (0.85)

–

Sayed, deLeur and Pump (2010)

–

30% (0.70)

–

–

–

Kar and Weeks (2009)

–

25% (0.75)

50% (0.50)

–

30% (0.70)

Torbic et al. (2009)

Urban two-lane

40% (0.60)

65% (0.35)

–

–

Torbic et al. (2009)

Rural two-lane

30% (0.70)

45% (0.55)

10% (0.90)

10% (0.90)

–

55% (0.45)

–

–

–

Rural two-lane

20% (0.80)

25% (0.75)

15% (0.85)

15% (0.85)

–

–

25% (0.75)

10% (0.90)

15% (0.85)

Hirasawa et al. (2006) Harkey et al. (2008) Persaud, Retting and Lyon (2004) 1

Fatal and serious injury.

Note: Crash reduction for FSI crashes is an important focus for the Safe System approach.

Where raised profile centrelines are installed on a road already featuring raised profile edgelines, the headon crash reduction benefits are even greater. Olson, Sujka and Manchas (2013) reported the following crash reductions:

 Crossover/head-on crashes – 65% reduction in head-on crashes (CMF of 0.35) – 25% reduction in FSI head-on crashes (CMF of 0.75)  Other crash types – 10% reduction in overall crashes (CMF of 0.90) – 25% reduction in FSI crashes (CMF of 0.75) – 10% increase in run-off-road to the left crashes (CMF of 1.10) – negligible impact on FSI run-off-road to the left crashes (CMF of 1.00). See the following Section 2.3 for further details on the performance of raised profile centrelines with edgelines.

Treatment life Austroads (2010f) suggests a treatment life of five years for raised profile centrelines.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

2.3

Raised Profile Centrelines and Edgelines

Olson, Sujka and Manchas (2013) reports that installing raised profile centrelines in concert with raised profile edgelines (Figure 2.4) was a particularly effective, low-cost method to address lane-departure (i.e. head-on and run-off-road) crashes on two-lane rural roads. Figure 2.4:

Raised profile centreline and edgeline treatment

Source: Transport for NSW (TfNSW), private communication, January 2015.

Crash modification Whilst Olson, Sujka and Manchas et al. (2013) report that raised profile edgelines led to a slight increase in the rate of head-on crashes, when installed with raised profile centrelines, both run-off-road and head-on crashes were reduced. Table 2.2 summarises a number of crash reduction and modification factors for the installation of raised profile centrelines and edgelines together, sourced from various references. As can be seen, this treatment type reduces both the incidence and severity of head-on crashes. It is suggested that the severity of head-on crashes is reduced as drivers are alerted to undertake a degree of emergency braking and/or steering input with the effect of reducing the ultimate impact speed. Lyon, Persaud and Eccles (2015) note that the results obtained in the study were conservative as not all sites used in the study were ideal candidates for this treatment and therefore the benefits were less notable. Generally, it would be expected that this treatment should yield even greater crash reductions than those presented in the study.

Treatment life As with raised profile centrelines, raised profile centrelines and edgelines together have a recommended treatment life of five years (Austroads 2010f).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Table 2.2:

Summary of crash reduction and modification (bracketed) factors for application of raised profile centrelines and edgelines

Range from all studies below

Head-on (all)

FSI headon(1)

All crashes

Lane-departure (all)(2)

FSI lanedeparture

35–65% (0.35–0.65)

30% (0.70)

20% (0.80)

20–65% (0.35–0.80)

45% (0.55)

20% (0.80)

25% (0.75)

Lyon, Persaud and Eccles (2015)

35% (0.65)

Olson, Sujka and Manchas (2013)

65% (0.35)

30% (0.70)

Sayed, deLeur and Pump (2010) 1 2

65% (0.35)

45% (0.55)

20% (0.80)

Crash reduction for FSI crashes is an important focus for the Safe System approach. Head-on crashes are a subset of lane-departure crashes and therefore included in this list.

2.4

Enhanced Pavement Markings

Enhanced pavement markings, also termed long life road markers, improve the reflectivity of road markers to improve their night time visibility. Smadi et al. (2010) demonstrate that increasing the retroreflectivity of centrelines helps to reduce the crash rate on roads during times of darkness. Head-on crashes and single vehicle crashes are identified as the target crash types affected by this treatment. However, Harwood et al. (2014) suggest that improved visibility of delineation is only effective on roads with good horizontal and vertical alignment. When applied on poorer quality roads, it can encourage higher speeds inappropriate for the environment and result in a general increase in crashes (Harwood et al. 2014). It has been suggested that improvements to the centreline marking visibility will be most effective when edgeline markings are similarly improved (Avelar & Carlson 2014).

Profiled thermoplastic centreline stripes Profiled thermoplastic centreline stripes are considered a moderate cost treatment that improves the visibility of a centreline system at night-time, particularly in wet conditions (Neuman et al. 2003). As it is a moderate cost, durable treatment, it is widely used (Bahar et al. 2006). Another advantageous feature appears to be that these features provide a mild audio-tactile response, alerting drivers straying from their lanes. However, the audio-tactile response is less noticeable for larger vehicles, especially trucks (Neuman et al. 2003). According to Neuman et al. (2003), this treatment suits road sections meeting the following conditions:

 sections with relatively long unbroken centrelines  traffic volumes and head-on crash history do not justify raised profile centrelines or other more expensive treatments

 wet-weather crashes are high  resurfacing or other pavement maintenance is not scheduled for at least three years. Cold applied plastic materials Cold applied plastic material is a two-part liquid mix of a resin-based material and a hardener. To improve reflectivity, glass beads are pre-mixed into the product, and additional beads are dropped on during application. Due to its high wear resistance, this treatment is generally used for marking intersections (VicRoads 2014).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Road marking tape Road marking tapes have a high initial cost compared to other linemarking options, so that their use is generally restricted to limited areas where a high level of performance is required under severe conditions, or to minor treatments to repair or replace sections of deteriorated linemarking. Tape may be produced flat or profiled and retroreflective glass beads are incorporated into the material during its production. Tape retroreflectivity is about four to six times that of waterborne traffic paints. However, their retroreflectivity quickly diminishes, with a useful life span of three years (Bahar et al. 2006). Figure 2.5 shows the installation of road marking tape for treating a short section. Figure 2.5:

Installation of road marking tape

Source: Main Roads Western Australia (MRWA), private communication, September 2015.

Crash modification Enhanced pavement markings can reduce night-time mid-block crashes by 10% (CMF of 0.90) (Migletz & Graham 2002). When isolating high crash frequency sites only, it is suggested that this treatment can reduce crashes by 15% (CMF of 0.85). Whilst these CRFs do not differentiate by crash type, it is generally accepted that this treatment has the greatest impact on run-off-road and head-on crashes (Donnell, Karwa & Sathyanarayanan 2009).

Treatment life Austroads (2010f) suggests a treatment life of five years for thermoplastic markings. For retroreflective tape, Bahar et al. (2006) indicate a useful treatment life of three years.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

2.5

Raised Reflective Pavement Markers

RRPMs, also sometimes known as retroreflective pavement markers, cats eyes or road studs, are used to augment the visibility of road markings. As the name suggests, the markers are raised, yet of trafficable profile, and are reflective such that they are illuminated by approaching vehicle headlights (AS 1742.2-2009). Figure 2.6 shows centreline RRPMs during daylight, whilst Figure 2.7 shows centreline RRPMs illuminated by headlights at night-time. Figure 2.6:

Centreline RRPMs during daylight

Source: ARRB Group. Figure 2.7:

Centreline RRPMs illuminated at night-time by headlights

Source: MRWA, private communication, September 2015.

RRPMs are conspicuous under a range of conditions, including wet night-time conditions. Additionally, they provide an audio-tactile signal when traversed by vehicle wheels, adding another stimulus to alert errant drivers (AS 1742.2-2009).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Centreline RRPMs may be placed 25–50 mm from either side of dividing lines. Centreline RRPMs should be yellow to differentiate them from edgelines RRPMs (red) or lane line RRPMs (white) (AS 1742.2-2009).

Crash modification Austroads (2010d) suggests that installation of RRPMs should reduce all types of crashes at a site by 5% (CMF of 0.95) for all crashes. It is suggested that this treatment may reduce all types of dry night-time crashes by 10% (CMF of 0.9), and all types of wet night-time crashes by 20% (CMF of 0.8) (Ermer et al. 1991 in Austroads 2010e). Gan, Shen and Rodriguez (2005) indicate a head-on crash reduction of 15% (CMF of 0.85) for this treatment.

Treatment life Austroads (2010f) suggests a treatment life of five years for RRPMs. However, the effective life of RRPMs depends critically on the precise location where they are installed. While a five-year life may be possible for an RRPM installed on the outside of an edgeline on a low-volume road, a much shorter life would be anticipated for an RRPM on a centreline that is frequently crossed by vehicles.

2.6

Internally Illuminated Pavement Markers

Internally illuminated pavement markers (IIPMs), also known as LED raised pavement markers or intelligent road studs, are a similar concept to RRPMs, but are self-illuminating. This serves to provide enhanced delineation, or delineation when RRPMs are not considered fully effective. Power may be provided via solar panels on the IIPMs, or through underground wiring (VicRoads 2005). Figure 2.8 shows a close view of a solar-powered centreline IIPM. Figure 2.8:

Close view of solar-powered centreline IIPM

Source: MRWA, private communication, September 2015.

It is opined that IIPM centrelines may be considered more effective than RRPMs on curves, crests or freeway ramps where the road alignment does not allow vehicle headlights to adequately illuminate RRPMs (VicRoads 2005). Otherwise, IIPMs may be preferable when it is important to provide delineation over longer distances than vehicle headlights may illuminate (Figure 2.9). IIPMs can provide illumination over 900 m, as compared to RRPMs, which can typically provide illumination from headlights over 90 m (Highway Engineering in Australia 2008).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Figure 2.9:

IIPMs illuminating over a long distance

Source: MRWA, private communication, September 2015.

Centreline IIPMs should still be retroreflective so they can provide some illumination even if the power source or internal electronics or lighting systems fail. They should retain the same colouring format as for RRPMs (i.e. yellow along centrelines) (AS 1742.2-2009; VicRoads 2005). IIPM’s are still an emerging technology, and some makes are more reliable than others. Practitioners should consult with their local jurisdiction for guidance on which IIPM products are preferred, and their level of reliability (MRWA, private communication, 27 November 2015).

Crash modification An extensive literature review has failed to identify crash modification factors for the installation of IIPMs. However, as they operate in a similar manner to RRPMs, but provide improved delineation over a longer distance, it is anticipated that crash reductions should be similar, and perhaps slightly higher, than those for RRPMs. However, more research should be done to quantify the in-service benefits of IIPMs.

Treatment life An extensive literature review has failed to identify any adopted service life values for IIPMs. In the absence of any such literature, it is assumed that they should have a similar service life as for RRPMs, i.e. five years (Austroads 2010f). It is possible that the service life may be lower, as the electronics in the system may require more frequent servicing. Also, Styles et al. (2003) report that, in some pedestrian-friendly locations, IIPMs were prone to vandalism or theft, and that IIPMs may be damaged more frequently due to traffic. Care should therefore be taken in selecting appropriate sites for installation, and ensuring routine maintenance of the markers.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

3. Median Treatments 3.1

Painted Median

Painted medians, also known as flush medians, are a low-cost option that addresses head-on crashes by improving lateral separation of vehicles and discouraging overtaking (Austroads 2010e). Figure 3.1 and Figure 3.2 show installations of painted medians on curved and straight road sections respectively. Figure 3.1:

Painted median on curve

Source: ARRB Group. Figure 3.2:

Painted median on straight section

Source: Department of Transport and Main Roads (TMR), private communication, November 2014.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Painted medians are generally preferable to raised medians where the roadway is too narrow to install a raised median (i.e. the associated clearances are not possible), or where the costs are not justified (Austroads 2010g). Narrowing the road through the installation of medians can also help to reduce travel speeds and encourage drivers to travel at a more appropriate speed for the environment presented to them. By travelling at lower speeds, drivers have more opportunity to avoid a collision, whilst the severity of any crash that may occur is reduced (Austroads 2014c). Austroads (2010g) specifies that the minimum width for painted medians should be 600 mm. However, Levett, Job and Tang (2009) report that the benefits of painted medians are maximised when they are at least 1.0 m wide. Cleaver, Jurisich and Dunn (2007) report that variations in median widths between 1.3 m and 3.1 m have negligible impact on the crash rate or severity of crashes. Therefore, it is suggested that medians should ideally be 1.0 m, after which median width should be based on the characteristics of the roadway, such as available road width and desirable lane widths. Figure 3.3 shows a schematic diagram of the layout of a painted median. When installing painted medians along roads prone to congestion, care should be taken that medians are not used by drivers to travel through illegally. This may be achieved by keeping median widths narrow or by installing pavement bars. Pavement bars also improve the effectiveness of the median (Section 3.2). Figure 3.3:

Typical layout of painted median

Notes:  Based on AS 1742.2-2009.  Pavement markers on the outside of an island are unidirectional RRPMs.  Diagonal rows of RRPMs within the marked median should be considered as an alternative to RRPMs along the outline. Two sets of RRPMs will not normally be required together.  N is generally 12 m for approaches to intersections. Source: Austroads (2010g).

Crash modification Roads and Maritime (2015b) suggests a 40% reduction in head-on crashes for painted medians (CMF of 0.60). Austroads (2010d) adopts a reduction in all crash types of 15–20% (CMF of 0.80–0.85) for the installation of painted medians.

Treatment life Austroads (2010f) adopts a treatment life of five years for painted medians. Austroads 2016 | page 17

Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

3.2

Pavement Bars

Pavement bars (also referred to as safety bars) are raised blocks located within the painted median, used to augment the median (Figure 3.4). Figure 3.4:

Example of pavement bars in median

Source: MRWA, private communication, September 2015.

Although traversable, they provide a very strong audio-tactile response, discouraging drivers from crossing them except in an emergency. They also improve the visibility of the median, particularly in wet conditions (Austroads 2009a). By discouraging drivers from traversing the median, pavement bars also discourage illegal overtaking manoeuvres (AS 1742.2-2009). This treatment should only be used on roads with 85th percentile speeds less than 75 km/h. For roads with higher speeds, RRPMs may be used to augment painted islands instead (AS 1742.2-2009). Pavement bars should also not be used on roadways with a width less than 6.8 m (Austroads 2009a). Pavement bars may be useful where raised medians may not be appropriate due to pavement width or lighting issues (AS 1742.2-2009). It is advised that they can be applied at relatively low cost and that they do not affect surface drainage (Austroads 2009a). When applying this treatment, the needs of motorcyclists and cyclists should be considered. It is suggested that bars should be spaced more than 2.0 m apart so they are greater than the typical wheelbase of motorcycles2. Use on curves should be avoided so as to prevent the destabilisation of motorcycles at this critical point (Austroads 2009a).

Crash modification An extensive literature search has failed to find any studies as to the effectiveness of this treatment in reducing crashes.

Treatment life No specific literature could be found identifying a treatment life for the installation of pavement bars. In the absence of any such literature, it is assumed that this treatment would have a similar service life to raised profile centrelines or RRPMs, i.e. five years (Austroads 2010f).

2

AS 1742.2-2009 permits shorter separation along the tapered section.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

3.3

Wide Centreline Treatment

Wide centrelines are a type of painted median treatment, also known as the narrow painted median strip treatment (Figure 3.5). Figure 3.5:

Examples of wide centreline treatments

Source: ARRB Group.

This treatment type typically provides a 1 m wide narrow median, increasing the separation of vehicles, but with negligible effect on vehicle travel speeds (Burdett 2011). Whilst 1 m wide centrelines are the advised width for this treatment, where geometric constraints do not allow for this, narrower wide centreline treatments are still expected to provide benefit, albeit reduced, and can be managed on a risk basis. The addition of raised profile linemarking (Section 2.2) increases the effectiveness of this treatment, alerting drivers should they deviate from their lane (Whittaker 2012). Figure 3.6 shows an example of a wide centreline treatment with raised profile linemarking. Installation of wide centrelines can generally be achieved within the space available on a two-way undivided road, e.g. a 1 m wide centreline can be formed by reducing each 3.5 m wide lane to 3.0 m wide (Whittaker 2012), or through a combination of narrowing the shoulder and lane widths (Neuman et al. 2003). However, lane and/or shoulder narrowing can only be achieved if road geometry after narrowing will still allow trucks and buses to be comfortably positioned away from the wide centreline (Neuman et al. 2003). Lane and shoulder narrowing limits a drivers ability to regain control of an errant vehicle, so practitioners should consider the occurrence of loss-of-control crashes on the roadway before implementing this treatment. Intuitively, reducing the width of the lane will have the effect of concentrating wheel paths, which may exacerbate rutting in certain situations. Where a road carries significant numbers of heavy vehicles or towed vehicles, reducing the lane width may require further consideration of its impact. Nevertheless, the benefits of introducing the wide centreline are considered to outweigh the disbenefits of narrowing the lanes to 3.0 m to accommodate them (Department of Transport and Main Roads 2013). An additional benefit of this treatment type is that it encourages lower travel speeds (Neuman et al. 2003).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Figure 3.6:

Layout of painted median outline with raised profile linemarking

Source: ARRB Group.

Neuman et al. (2003) advise that care should be taken when narrowing shoulders to ensure that:

 the treatment does not result in greater risk of FSI collisions with roadside objects  there is adequate protection in the shoulder for broken-down vehicles. The treatment may be further complemented with alternating white diagonal strips and yellow diagonal reflective markers to further highlight the median strip (Whittaker 2012). Alternatively, in Germany the median is highlighted with green surface markings (Traffic Technology Today 2014). Figure 3.7:

Wide centrelines highlighted by RRPMs and coloured linemarkings respectively

(a) RRPMs

(b) Green linemarkings

Source: Whittaker (2012).

Source: Traffic Technology Today (2014).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Unlike other median treatments, wide centrelines may be designed to permit drivers to cross into the opposing travel lane to perform overtaking manoeuvres, through the use of broken wide centreline markings (Lilley 2012; Connell, Babic & Pattison 2011). Examples of centreline markings to allow for overtaking for traffic travelling in either direction and for traffic travelling in one direction only are shown in Figure 3.8. Care should be taken to ensure that overtaking is only permitted at appropriate locations. Wide centreline treatments also provide the potential to have wire rope median barriers (WRMB) retrofitted on them (Austroads 2009b). If the intention is for WRMBs to ultimately be added, road designers need to consider whether a 1.0 m wide median is appropriate. As explained in Section 3.6.3, WRMBs are most effective when located on medians wide enough to contain barrier deflection within the median. It is suggested that in such circumstances it would be more effective to ensure the median is of sufficient width to cater for the safe performance of WRMBs at the initial point of median installation. Figure 3.8:

Example of wide centreline designed to allow for overtaking for both flows of traffic and one flow of traffic respectively

(a) Both flows of traffic

(b) One flow of traffic

Source: DPTI, private communication, December 2014.

Source: TfNSW, private communication, January 2015.

Crash modification Wide centreline treatments have been found to lead to an 80% reduction in head-on crashes (CMF of 0.20), and a 60% reduction of total crashes (CMF of 0.40) (Whittaker 2012). TfNSW (Private communication, April 2015) have adopted a 50% head-on crash reduction factor for this treatment (CMF of 0.50). As an additional benefit, this treatment has been found to lead to a 60% reduction in run-off-the-road to the left crashes (CMF of 0.40) (Whittaker 2012).

Treatment life Wide centreline treatments should have a similar treatment life to standard centrelines, i.e. three years for standard linemarkings, and five years when using raised profile linemarkings (Austroads 2010f).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

3.4

Raised Median

Raised medians, whilst more expensive than painted medians, are often preferred for their conspicuity and physical deterrent effect in preventing cross-median manoeuvres. Raised medians can also accommodate signposting, lighting and traffic signal hardware, and may be landscaped, improving aesthetics and restricting headlight glare (Austroads 2010g). Typically, raised medians are more common on urban and semi-urban roads than rural roads. Figure 3.9 shows an example of a paved raised median, whilst Figure 3.10 shows a grassed raised median which, as well as separating traffic, provides locations for signage and lighting. Figure 3.9:

Paved raised median

Source: ARRB Group. Figure 3.10: Grassed raised median providing shelter for signs and lighting

Source: ARRB Group.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

When deciding upon the introduction of a raised median, the following factors should be considered (Austroads 2010g), whether:

 any artificial lighting needs to be provided  the raised medians are likely to affect drainage and the steps needed to address this  additional roadway space will be required to store immobilised vehicles and for offset to median kerbs. The kerbing used in raised medians should be semi-mountable and clearly delineated (Austroads 2010g). Additionally, raised medians on roads prone to congestion should not be appealing to drivers to use as a transit lane (Figure 3.11). This could be achieved by keeping the median width below 2.8 m, or installing frangible signage posts at regular intervals along the median. Figure 3.11: Drivers using raised median as transit lane on congested road

Source: Haynes (2009).

Crash modification Roads and Maritime (2015b) indicates that the installation of raised medians may reduce head-on crashes by as much as 60% (CMF of 0.40). Schultz et al. (2011) report that installation of raised medians may lead to a 40% reduction in the total crash rate (CMF of 0.60), and a 45% reduction in the FSI crash rate (CMF of 0.55). Austroads (2010d) indicates a likely 45–55% reduction in all crashes (CMF of 0.45–0.55) with the installation of raised medians.

Treatment life Austroads (2010f) recommends a treatment life of 20 years for raised medians.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

3.5

Barrier Kerbing on Median

Barrier kerbing may be used to delineate the median and provide a narrow physical obstacle to head-on crashes (Figure 3.12 to Figure 3.25). This kerb type should ideally be 150 mm high to prevent vehicles traversing the kerb at low to moderate speeds. This treatment should also only be used on roads with speed limits of 70 km/h or under, as at higher speeds, the kerb may result in errant vehicles rolling over or becoming airborne (Main Roads Western Australia 2014). It is suggested that, when used on medians, an offset of at least 0.3 m should be provided, although 0.6 m is preferable. As this treatment creates a sense of restriction and does not allow for additional space for rear trailer sway, this kerbing is not recommended on narrow roads or those where a high percentage of traffic is expected to be heavy vehicles (Main Roads Western Australia 2014). Whilst being a physical impediment to median crossover, will be unable to prevent most vehicle crossovers. Barrier kerbing can be formed by bespoke units or pre-cast concrete kerbing units placed back-to-back to form the required profile. Figure 3.12: Example of median barrier kerbing

© 2015 Google

Source: Google Maps (2015), ‘New South Wales’, map data, Google, California, USA. Figure 3.13: Further example of median barrier kerbing

Source: ARRB Group.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Crash modification An extensive literature search has failed to identify any literature identifying crash modification factors for this treatment. It is recommended that such investigations be conducted in the future.

Treatment life In the absence of literature indicating a service life for this particular treatment, it is assumed this treatment will have a similar treatment life to other kerb and median treatments, for which Roads and Maritime (2015b) has adopted a 30-year service life.

3.6

Median Barriers

Median barriers minimise the possibility of an errant vehicle crossing into the path of traffic travelling in the opposite direction. It is stated that unless crash history at the site warrants it, median barriers are not necessary when medians are wide enough or traffic volumes low enough that head-on crash risk should be low (American Association of State Highway and Transportation Officials 2011). Consideration for the use of median barriers should be given based on road environment, anticipated traffic volumes and an assessment of the risks based on road geometry (Austroads 2010i). For instance, VicRoads (2003 in Austroads 2010i) specifies that, on freeways with speed limits of 100–110 km/h, median barriers should be provided:

 where the annual average daily traffic (AADT) will exceed 30 000 vpd within 5–10 years  where the AADT will reach between 20 000 and 30 000 vpd within 5–10 years and the separation between opposing traffic is less than 6 m

 where a risk assessment indicates a need for the barrier for any other reason. A detailed overview of median barriers, including guidance on their selection and installation may be found in Part 6 of the Austroads Guide to road design (Austroads 2010c). Barriers used on Australian and New Zealand roads must comply with the Australian and New Zealand Standard AS/NZS 3845.1:2015: Road safety barrier systems and devices part 1: Road safety barrier systems. Recent research has indicated that, following the installation of median barriers, the crash rate at a site will generally increase. However, and aligned with Safe System principles, the severity of such crashes will decrease, i.e. high-severity head-on crashes resulting from median crossovers will be replaced with more controlled crashes of lower severity into median barriers (Chimba et al. 2014). Road safety barriers dissipate kinetic energy of a vehicle crash into a more manageable form of energy, such as (AS/NZS 3845.1:2015):

   

heat through friction elastic or plastic deformation of components of the barrier and/or vehicle fracture of components of the barrier and/or vehicle, or both controlled displacement of the barrier and/or vehicle, such as lifting of the vehicle.

The transfer of energy needs to be achieved in a controlled manner. It is therefore important to ensure that no unintended snagging of the vehicle occurs, which may lead to unsafe vehicle movements such as rolling, yawing, or excessive deflection into nearby vehicles (AS/NZS 3845.1:2015).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Depending on the type of barrier and its purpose, median barriers are generally designed to pass crash tests featuring private vehicles or small trucks, and impacting at angles between 15–25°, and at speeds of 50–100 km/h. Larger vehicle mass or size, impact angles, or impact speeds compromise the barrier’s ability to restrain the vehicle. This has led some to opine that median barriers should be avoided on tight curves when possible (Ross et al. 1993; Transport for NSW 2012). However, such usage is included in the pertinent Australian Standard AS/NZS 3845.1:2015, with consideration of a reduction in traffic speed or using a median barrier with a high performance level. When considering the implementation of median barriers, the following issues should be taken into account:

      

likely crash severity costs per crash, considering both injury and property damage costs minimum required width for safe use of barrier impact of the barrier on sight distance and aesthetics influence of barrier on drainage safety of motorcyclists (Section 3.6.6) barrier terminal treatments (Section 3.6.7) (Austroads 2010c).

The median width required for installation of a barrier will be dependent on the barrier width and the required clearance between the barrier and the traffic edgeline. Required clearance will depend on the expected deflection of the barrier during impact with a design vehicle, as well as a nominal clearance at which drivers will feel comfortable driving alongside the barrier (Austroads 2010c). Ideally, the maximum deflection of the barrier should be less than half the median width in order to prevent penetration of the barrier into opposing traffic (American Association of State Highway and Transportation Officials 2011) (Figure 3.14). However, median barriers retrofitted on narrower medians have been proved to work successfully when needed (Marsh & Pilgrim 2010). Figure 3.14: Deflection of errant vehicle by wire rope median barrier

Source: ARRB Group.

Rigid barriers work adequately where there is no room for deflection. However, flexible barriers provide for better dissipation of energy, thus reducing the severity of crashes. The disbenefit is that flexible barriers need more space to deflect without encroaching into the stream of opposing traffic. An increased risk of penetration exists with wire rope barriers. The relative effectiveness of different median barriers in reducing FSI crashes can be viewed in Table 3.1, which presents the FSI crash ratio3 for each barrier option.

3

The number of fatal or serious injury crashes resulting from running into a crash barrier, divided by the total number of such crashes.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Table 3.1:

FSI crash ratio for safety barrier solutions

Median barrier option All

1

2

3

Rural 100 km/h

Rural 110 km/h

types(1)

0.46(2)

0.61(2)

Rigid

0.50(3)

0.50(3)

Semi-rigid

0.60

0.56

Flexible

0.33(3)

0.33(3)

There was indication that FSI crash ratios increased with barrier offset from the edge line at about 0.03 per metre. This trend was only demonstrated for semi-rigid and flexible barriers on high-speed roads. The evidence was not consistent for all barrier types in all speed environments due to the small sample size of crashes into barriers with large offset. A relevant scaling factor could be applied to barrier FSI crash ratios if barriers are proposed to be placed significantly further away from the edge line than each barrier's typical application range (2–4 m). The result for ‘all types’ is based on all available barrier crash data and larger sample sizes. Thus, it may be different to a weighted average of the results for rigid, semi-rigid and flexible barriers which were based on a smaller data set of manually selected crashes according to the method documented in Austroads (2014b). Based on a sample from Victorian 100 km/h urban freeways – insufficient data was available on rural roads.

Source: Modified from Table 7.6 of Austroads (2014b).

Crash modification Elvik and Vaa (2004) indicate that the installation of any type of median barrier on a divided highway should result in a 25% increase in crashes (CMF of 1.25). However, the injury crash rate would reduce by 30% (CMF of 0.70) and the fatal crash rate would decrease by 45% (CMF of 0.55). This study does not distinguish by crash type – it is likely that the increase in crashes would be primarily due to an increase in run-off-road into median barrier crashes, whereas a decrease in injury crashes would be attributed to a significant reduction in head-on crashes, replaced by less severe run-off-road collisions.

3.6.1 Rigid Median Barriers Rigid median barriers are generally concrete barriers (Figure 3.15), used when space available for deflection is very limited (Jama et al. 2011). These barriers are generally costly to install (Alba et al. 2014). Figure 3.15: Example of concrete rigid median barrier

Source: ARRB Group.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Rigid barriers can be used on medians as narrow as 0.8 m, but, in such cases, the barrier would consume the entirety of the median space (Austroads 2010i). Ideally, rigid barriers should not be offset more than 3.0 m from the edge of a trafficable lane, and never more than 4.0 m. With any greater offset, angles of impact would be large, such that severe injuries become more likely (Austroads 2010c). The minimum length (run) of rigid barriers should be 20–30 m. Drainage provisions should be considered to prevent stormwater flooding. Concrete barriers can also be difficult to see at night-time due to their limited contrast with the roadway pavement, particularly under wet conditions and/or when drivers are affected by headlight glare (Roads and Traffic Authority 2010). The practitioner should therefore consider including linear delineation on the concrete barrier, particularly on curves (Figure 3.16). Figure 3.16: Linear delineation of concrete barrier on a curve

Source: ARRB Group.

Crash modification Tarko, Villwock and Blond (2008) indicate that concrete median barriers will eliminate all cross-median crashes (CMF of 0). However, as indicated previously, concrete median barriers do result in an increase in run-off-road to the right crashes into the barriers, with a 120% increase in single vehicle crashes (CMF of 2.2, i.e. more than double). The increased crashes were of much lower severity than the head-on crashes. Whilst Tarko, Villwock and Blond (2008) indicated a slight increase in all casualty crashes, the report does not distinguish between severity outcomes. Due to a likely increase in single vehicle crashes, Elvik and Vaa (2004) deduce that there would be a 15% increase in injury crashes. However, this study does not distinguish between minor and severe injuries, nor are separate crash reductions indicated by crash type. Gan, Shen and Rodriguez (2005) indicate that installation of concrete median barriers should reduce all fatal crashes by 90% (CMF of 0.10) and injury crashes by 10% (CMF of 0.90).

Treatment life Austroads (2010f) recommends a treatment life of 30 years for rigid median barriers.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

3.6.2 Semi-rigid Median Barriers Semi-rigid median barriers provide a degree of deflection to absorb some energy from impact in minimal road space. These barriers generally fall under three different categories:

 W-beams, consisting of W-shaped steel beams facing traffic, supported by steel or wooden posts  thrie-beams, similar to a W-beam but with more corrugations and a higher mounting position. They provide increased rigidity and are typically able to contain larger vehicles

 tubular beams of various hollow shapes (e.g. rectangular) supported by posts  steel tubular section on bridge barriers (Jama et al. 2011). Examples of the most common W-beam barrier in use along a wide and narrow median are shown in Figure 3.17 and Figure 3.18 respectively. Figure 3.17: W-beam barrier along wide median

Source: ARRB Group. Figure 3.18: W-beam barrier along narrow median

Source: ARRB Group.

When placing back-to-back semi-rigid barriers on curve medians, consideration should be given to ensure that the inside barrier maintains sufficient tension in the rail to perform as designed (Austroads 2010c). Specific manufacturer requirements will apply. The minimum length of installation for semi-rigid barriers should typically be 30 m (Austroads 2010c).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

When installing semi-rigid barriers near kerbs, they should either be installed within 200 mm of the kerb or some distance behind to avoid the kerb/barrier configuration from causing vehicles to vault over the barrier (Austroads 2010c).

Crash modification Alluri, Haleem and Gan (2013a) report that W-beam barriers prevent 95% of cross-median crashes (CMF of 0.05), including almost 100% of crashes involving cars (CMF of ~0.00) and 90% of crashes involving light trucks (CMF of 0.10). The effectiveness for medium and heavy trucks was lower with reductions of 80% (CMF of 0.20) and 75% (CMF of 0.25) respectively.

Treatment life Austroads (2010f) recommends a treatment life of 30 years for semi-rigid median barriers.

3.6.3 Wire Rope Median Safety Barriers Wire rope median safety barriers (WRMBs), also called wire rope safety fences (WRSF) or cable barriers, are essentially flexible crash barriers. The barrier uses steel cables supported by collapsible posts to absorb energy, contain errant vehicles and redirect them back towards their intended path. The system was first introduced to New South Wales in 1991, and is now in use in all jurisdictions in Australia (Austroads 2009b). WRMBs as a means to prevent crossover crashes may be applied on a median or along wide centrelines (Figure 3.19) (Austroads 2009b). When undivided roads are upgraded to wide centrelines with WRMBs, traffic has been found to travel further from the centre of the road, such that vehicles are both physically restrained, and also have a greater buffer to avoid head-on and run-off-road to the right crashes (Marsh & Pilgrim 2010). Figure 3.19: WRMB in wide centreline

Source: ARRB Group.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Whilst barrier selection is made on a case-by-case basis depending on the specific needs of a site, WRMBs are often favoured over rigid or semi-rigid barrier systems. Early findings from the use and outcomes of WRMBs, reported in Austroads (2009b) show generally favourable results. As this infrastructure technology has progressed and various products of this type have come onto market, evaluation and research continues into the performance, whole-of-life costs and implementation aspects of such provision. The reader is advised to consult with their local jurisdiction as to policies on the use and maintenance of WRMBs. Whole of life costs for WRMB will vary depending on the barrier specification and its maintenance schedule as well as the likely rate of collisions into the barrier (and subsequent need for repairs). Indications are that some situations, other barrier types or alternate treatments may prove more cost effective. When considering the installation of wire rope barriers, the following factors should be considered (Austroads 2010c):

 lateral slope should typically not exceed 10:1  care should be taken to ensure adequate tension (before, during and after an impact) on WRMBs where horizontal curve radius is less than 600 m

 WRMBs may not be appropriate on sag vertical curves as: – tension may lift poles out of the ground (particularly during cold weather) – the WRMB may be elevated over the sag allowing the vehicle bonnet to pass under the barrier so that the ropes may make contact with and encroach into the occupant compartment

 WRMB should not connect directly to other barrier types and should be positioned such that the other barriers do not interfere with WRMB deflection. Ideally, WRMBs should be located on medians wide enough that barrier deflection will not cross over into opposing traffic. However, this is not always possible on brownfield sites, and the installation of WRMBs on a narrow median often provides greater safety benefits than any associated risks. Appendix H of Part 6 of the Austroads Guide to road design (Austroads 2010c) provides additional guidance on the installation of WRMBs on narrow medians. It is highlighted that a WRMB system cannot remain continuous for very long stretches of road. Adjacent WRMBs need to overlap in such a manner that the anchor point angled towards one stream of traffic is shielded by the other WRMB system, as shown in Figure 3.20. Figure 3.20: Overlapping of WRMB systems

Source: ARRB Group.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Crash modification Table 3.2 summarises a number of head-on, single-vehicle and FSI crash reduction and modification factors for the installation of WRMBs, sourced from various references. Table 3.3 presents further factors based on varying levels of crash severity. As can be seen, despite an increase in total crashes, the severity of crashes is significantly reduced which, as explained earlier, is a major consideration within the Safe System approach to road safety. Table 3.2:

Summary of crash reduction and modification (bracketed) factors for WRMB treatment of head-on, single-vehicle and FSI crashes extracted from selected studies Study

Head-on

Single-vehicle

FSI crashes

60–95% (0.05–0.40)

–40 to –95% (1.40–1.95)

0–75% (0.25–1.00)

TfNSW (Private communication, April 2015)

95% (0.05)

–95% (1.95)

–

Villwock, Blond and Tarko (2009)

95% (0.05)

–70% (1.70)

Negligible(1) (1.0)

Alluri, Haleem and Gan (2013b) – all

80% (0.20)

–40% (1.40)

25% (0.75)

Alluri, Haleem and Gan (2013b) – cars

–

–

10% (0.90)

Alluri, Haleem and Gan (2013b) – light trucks

–

–

35% (0.65)

Alluri, Haleem and Gan (2013b) – motorcycles

–

–

75% (0.25)

Olsen et al. (2011)

60% (0.40)

–

45% (0.55)

Candappa et al. (2009)

85% (0.15)

–

65% (0.35)

Range of studies

1

It should be noted that this refers to a negligible change in the number of FSI crashes, not the number of fatal or serious injuries. Presumably, even if the number of FSI crashes did not change, a shift to single-vehicle crashes from head-on crashes would result in fewer vehicles involved and therefore, fewer crash casualties.

Note: Crash reduction for FSI crashes is an important focus for the Safe System approach. Table 3.3:

Crash modification factors for crashes of varying severity extracted from selected studies Study

Alluri, Haleem and Gan (2013b) – crash rate Nilsson and Prior (2004) – casualty numbers

Fatal

Serious injury

Minor injury

Property damage only

All

0.58

0.80

0.88

1.88

1.38

050–0.65

0.55–0.70

~1.0

1.30

–

Chimba et al. (2014) found that crashes into WRMBs increased with increasing:

     

shoulder width (a counter-intuitive finding) differential elevation degree of curve traffic volume speed limit number of curves.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Crashes decreased with an increase in (Chimba et al. 2014):

 number of lanes  cable offset  median width. These variables suggest that, with greater lateral distance, drivers should be able to regain control of errant vehicles, preventing a collision with the WRMB (Chimba et al. 2014).

Treatment life Roads and Maritime (2015b) adopts a service life of 30 years for this treatment. Studies have shown that WRMBs are cheaper to install, but have higher maintenance costs than other median barriers as they require periodic retensioning of the cables due to general wear and tear (Neuman et al. 2008). A benefit of WRMBs is that, after a collision, repairs can be done much faster, often taking a matter of minutes. This generally involves removing damaged posts and inserting new posts into the sockets. In terms of anticipated strikes, when used in wide centrelines, barriers are expected to be struck every 1–2 million vehicle kilometres. When used in conjunction with audio-tactile linemarkings, the strike rate is anticipated to be lower (Marsh & Pilgrim 2010).

3.6.4 2+1 Roads WRMBs are used extensively in Sweden in a design layout referred to as a ‘2+1 road’. Whilst this treatment is not a typical median treatment, it is prudent to include mention of this highly successful scheme. The 2+1 road design involves a three-lane cross-section. The outside lanes serve as a general traffic lane for one direction each. The centre lane serves as an overtaking lane for each direction of traffic, alternating every 1–2.5 km, with a transition zone of up to 300 m in length (Figure 3.21) (Austroads 2009b). Figure 3.21: Typical 2+1 road configuration

Source: ARRB Group.

An example of an Australian 2+1 road configuration is shown in Figure 3.22. In the foreground of this image, approaching traffic has an overtaking lane, whilst departing traffic has only one lane. In the background, departing traffic has an overtaking lane, and the tapered beginning of the approaching overtaking lane can be seen.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Figure 3.22: 2+1 roadway

Source: ARRB Group.

The 2+1 layout has been applied on roads with speed limits of between 90 km/h and 110 km/h with significant safety benefits, and is therefore seen as one of the key contributors to the Safe System approach. It is reported that the layout has resulted in an 80% reduction in fatalities, and a 55% reduction in severe injuries (Bergh et al. 2003 in Austroads 2009b). It is considered that this treatment is suitable for consideration for roads with an overtaking head-on crash history, for which traffic flows are not sufficient to support a dual divided carriageway (Department of State Growth Tasmania 2014). The treatment is recommended for roads with traffic flows rates of up to 1200 veh/h in one direction of travel (Derr 2005). A typical 2+1 road cross-section on a 13 m wide carriageway would include (Austroads 2009b):

   

1.25 m wide median 3.25 m lanes for the two-lane direction 3.5 m lanes for the one-lane direction 0.75 m hard shoulders on each side of the carriageway (Figure 3.23).

Figure 3.23: Typical 2+1 road cross-section

Source: ARRB Group.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Crash modification It has been found that converting a 13 m wide road to a 2+1 road with a WRMB reduced fatal crashes (all crash types) by 80% (CMF of 0.20). For motorcyclists, the number of FSI crashes (all crash types) was reduced by 40–50% (CMF of 0.60–0.50) by the introduction of 2+1 roads (Carlsson 2009). When analysing such roads by speed limit (Carlsson 2009):

 110 km/h roads returned 75% reduction in the fatal crash rate (CMF of 0.25)  90 km/h roads returned an 80% reduction in the fatal crash rate (CMF of 0.20). Bergh et al. (2003 in Austroads 2009b) report that 2+1 roadways have reduced fatal crashes by 80% and severe injury crashes by 55% (CMFs of 0.20 and 0.45 respectively).

Treatment life An extensive literature search has failed to identify any adopted service life values for the installation of 2+1 roadways. In the absence of these values, it is assumed that this treatment should have a service life similar to that of WRMB, i.e. 30 years (Roads and Maritime 2015b).

3.6.5 Moveable Barriers Moveable delineation and barrier systems have been used where tidal flow is sought on a road space during peak traffic periods. Systems have developed in time, such that some are now capable of deflecting errant vehicles and be relocated during the day to cater for alternating traffic flow peaks (Figure 3.24). These systems can be designed to consume as little as 0.30 m road space and can eliminate head-on crashes in situations where this may not at first appear possible (World Highways 2015). Lane changeovers can be done quickly. The Auckland Harbour Bridge moveable barriers (2 km length) take 30 minutes to transfer, including 10 minutes setting up the machinery (Resolve Group, private communication, July 2015). A further example is the moveable barrier system on Victoria Road in Sydney, which has been in operation since 2011. Figure 3.24: Images of moveable barrier being transitioned, including over Auckland Harbour Bridge (right)

Source: World Highways (2015).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Crash modification In the absence of any literature identifying crash modification factors for moveable barriers specifically, this treatment would be expected to have similar crash modification outcomes to other concrete barriers (Section 3.6.1).

Treatment life With refurbishment, moveable barriers have an indefinite treatment life (Resolve Group, private communication, July 2015).

3.6.6 Motorcyclist Concerns with Median Barriers Integral to the Safe Systems approach is providing a safe road environment for all road users, i.e. including motorcyclists. Concerns have been raised as to the compatibility of median barriers with collisions involving motorcycles. Whilst the proportion of fatal motorcycle crashes involving safety barriers is low at 5.4% in Australia, this is very high relative to the fatality rate for car occupants (Jama et al. 2011; Bambach, Grzebieta & McIntosh 2013). In Europe, whilst collisions with safety barriers are a factor in 8–16% of motorcyclist deaths, motorcyclists are 15 times more likely to sustain fatal injuries from colliding with a barrier than a car occupant in the same impact (EuroRAP 2008). In the USA, motorcyclists have an 80 times greater risk of sustaining fatal injuries from a barrier collision than car occupants (Gabler 2007). As a result of the increased risk, protection for motorcyclists has been mandated when using guardrails in Portugal and the Netherlands (Delhaye 2011). Despite the concerns, it is believed that motorcyclist safety is improved by the presence of median barriers. Whilst they may present their own hazards to motorcyclists, they also contain errant vehicles in opposing traffic. This reduces the risk of motorcyclists being involved in high-severity head-on collisions with errant vehicles (EuroRAP 2008). Concrete barriers are generally preferred by motorcyclists as, having a smooth concrete surface, the barriers distribute forces more evenly when motorcyclists are thrown against them, reducing injuries (Alba et al. 2014). The most common type of reported motorcycle-into-barrier crash in Australia and New Zealand is from collisions with steel W-beam barriers (Grzebieta, Bambach & McIntosh 2013). Barrier support posts present the greatest hazard for motorcyclists. Injuries from motorcyclist collisions with barrier support posts can be five times as severe as other motorcyclist collisions (EuroRAP 2008). The next most critical issue is the presence of protrusions along the top of barriers which can serve as sharp cutting edges acting against motorcyclists sliding along the top of a barrier (Grzebieta, Bambach & McIntosh 2013).

Modified or shielded posts As the posts present the greatest source of harm for motorcyclists, modifications to these posts have been considered by many manufacturers and road designers (Austroads 2010b). Posts with a sigma (Σ), Z or C cross-section are less harmful to motorcyclists compared to an I-shaped cross-section. In Australia, C-posts are the most commonly used (Alba et al. 2014; EuroRAP 2008). Post protectors can be fitted onto wire rope safety barriers or steel barriers (Figure 3.25a). These cover the posts, shielding motorcyclists from the barrier post edge. The barrier post edge, in particular its sharpness, is the most harmful factor in a motorcyclist impact. Post protectors are made of energy-absorbent material such as polystyrene, and they last four years. They are most effective in low-speed collisions, such as in urban areas or on tight curves (Austroads 2010b). These protectors should only be used once testing has confirmed they do not affect barrier performance. Rub rails may be installed along the underside of W-beam barriers to allow riders thrown from the motorcycles to slide along without being injured by the posts (Figure 3.25b) (Austroads 2010b).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Figure 3.25: Examples of motorcycle barrier post protection systems (see Section 1.6)

(a) Post protector

(b) Rub rail

Source: Ingal Civil (2015a).

Source: Ingal Civil (2015b).

3.6.7 Median Barrier Terminal Treatments The ends of barriers present potential hazards when struck by errant vehicles, so the terminal design should be considered carefully. Along with other considerations, barrier terminals should not (Austroads 2010c):

 stop an errant vehicle abruptly  cause a vehicle to roll, vault or yaw inappropriately  penetrate into the occupant space of the vehicle. Part 6 of the Austroads Guide to road design (Austroads 2010c) provides guidance on the appropriate selection of terminal treatments.

3.7

Flexible Bollards

Flexible bollards, also known as safe-hit posts, provide a visual separation and physical obstacle between opposing streams of traffic (Figure 3.26). They are a possible treatment where there is insufficient road space for the installation of a traditional median or median barrier and are often installed in conjunction with barrier kerbs (Section 3.5) (Partridge 2015). Flexible bollard systems may occupy the same space as wire rope barriers, allowing for their retrofitting if required (Figure 3.27). The features are fully flexible and are not designed to physically prevent vehicles from crossing the median. This treatment has been seen to reduce vehicle travel speeds slightly and encourages drivers to travel further from the median (Mackie, March & Pilgrim 2011).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Figure 3.26: Flexible bollards on motorway

Source: ARRB Group. Figure 3.27: Flexible bollards that may later be replaced with WRMB

Source: Mackie, March and Pilgrim (2011).

Crash modification An extensive literature search has failed to identify any indications of crash modifications for this treatment. It is recommended that more research be conducted to investigate the benefits of flexible bollards as a median treatment, both in isolation and in combination with other treatments.

Treatment life An extensive literature review has failed to identify any adopted service life values for flexible bollards. In the absence of any such literature, it is assumed that they should have a similar service life as for RRPMs, i.e. five years (Austroads 2010f).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

3.8

Median Turning Bays

Whilst primarily a treatment to allow turning into driveways and entrances with minimal rear-end crashes, studies have shown that the installation of median turning bays (known in New Zealand as flush medians) also help to reduce head-on crashes. These bays serve to provide a buffer between opposing directions of travel (Neuman et al. 2003). Figure 3.28 presents a diagram demonstrating the operation of median turning bays, whilst Figure 3.29 presents an example of a median turning bay. Figure 3.28: Diagram of operation of median turning bays

Source: Adapted from Roads and Maritime Services (2015a). Figure 3.29: Example of median turning bay

Source: ARRB Group.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Median turning bays help to reduce head-on crashes in two ways:

 They give the driver a more protected location to judge acceptable gaps in the oncoming flow. This in turn reduces driver pressure, encouraging the driver to make safer decisions.

 They provide a painted median between opposing vehicles, providing the safety benefits of such medians, as discussed in Section 3.1 (Neuman et al. 2003). Median turning bays can be installed on four-lane undivided roads by modifying the layout to a three-lane roadway with a median turning bay. Alternately, two-lane roads can be reconstructed to include a median turning bay (Neuman et al. 2003).

Crash modification Based on expert opinion alone, Gan, Shen and Rodriguez (2005) suggest that this treatment should reduce head-on crashes by 35% (CMF of 0.65), and all crash types by 30% (CMF of 0.70).

Treatment life CMF Clearinghouse (2015) recommends a service life of between 7 and 20 years for this treatment.

3.9

Median Design

3.9.1 Median Width Wider medians provide a greater recovery area for a driver to correct the position of an errant vehicle. They may also reduce the impact of headlight glare and give drivers a greater sense of separation from opposing vehicles. As such, the rate of head-on crashes has been found to be inversely related to the width of medians. This is inclusive of the median shoulder width (Neuman et al. 2008). Similarly, whilst wider medians reduce the risk of a crossover incident, computer simulations indicate a disbenefit in the form of an increase in susceptibility to roll-over incidents (Stine et al. 2010).

Crash modification The safety benefits of widening medians based on the road environment are outlined in Table 3.4 for fullaccess controlled medians (i.e. no at-grade crossings) and in Table 3.5 for partial-access controlled medians or no-access controlled medians (i.e. intermittent at-grade crossings). These findings are based on there being no median barriers. Table 3.4:

Crash modification factors for full-access controlled medians based on width Rural 4 lanes

Urban 4 lanes

Urban 5+ lanes

Median width (m)

All

Crossmedian

All

Crossmedian

All

Crossmedian

3.05 6.10 9.14 12.19 15.24 18.29 21.34 24.38 27.43 30.48

1.00 0.96 0.93 0.90 0.87 0.84 0.81 0.78 0.75 0.73

1.00 0.86 0.74 0.63 0.54 0.46 0.40 0.34 0.29 0.25

1.00 0.95 0.90 0.85 0.80 0.76 0.72 0.68 0.65 0.61

1.00 0.89 0.80 0.71 0.64 0.57 0.51 0.46 0.41 0.36

1.00 0.93 0.86 0.80 0.74 0.69 0.64 0.59 0.55 0.51

1.00 0.89 0.79 0.71 0.63 0.56 0.50 0.45 0.40 0.35

Source: Adapted from Harkey et al. (2008).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Table 3.5:

Crash modification factors for partial-access controlled or no-access medians based on width Rural 4 lanes

Median width (m) 3.05 6.10 9.14 12.19 15.24 18.29 21.34 24.38 27.43 30.48

Urban 4 lanes

All

Cross-median

All

Cross-median

1.00 0.95 0.91 0.87 0.83 0.79 0.76 0.72 0.69 0.66

1.00 0.84 0.71 0.60 0.51 0.43 0.36 0.31 0.26 0.22

1.00 0.95 0.90 0.85 0.81 0.77 0.73 0.69 0.65 0.62

1.00 0.87 0.76 0.67 0.59 0.51 0.45 0.39 0.34 0.30

Source: Adapted from Harkey et al. (2008).

Treatment life An extensive literature search has failed to identify an appropriate treatment life for wide medians. In the absence of any such literature, it is assumed that median width modifications would have a similar service life to that of median installations, i.e. five years for painted medians and 20 years for raised medians (Austroads 2010f).

3.9.2 Cross-section Depressed medians with an inverted trapezoidal shaped cross-section have a theoretically lower incidence of crossover incidents than medians with a v-ditch shaped cross-section. In a computer simulated environment, about 22% fewer incidents of crossovers occurred when the median had an inverted trapezoidal shape (Stine et al. 2010) Median grade needs to be carefully controlled. Steeper grades have a lower risk of median crossovers, but a higher risk of roll-over incidents (Stine et al. 2010). Austroads (2010i) suggests that depressed medians should have a gradient of between 6:1 and 25:1 (10:1 being desirable); raised medians have a recommended gradient range of between 6:1 and 33:1.

Crash modification Stine et al. (2010) demonstrate that use of an inverted trapezoidal shape could reduce head-on crashes by 20% compared to those with a v-ditch shaped cross-section (CMF of 0.80).

Treatment life CMF Clearinghouse (2015) suggests a service life of 10–20 years to changes to median slope.

3.9.3 Pavement Edge Drop-off Edge drop-off (Figure 3.30) between the roadway and the median can affect a driver’s ability to regain control of an errant vehicle, and is therefore related to the incidence of head-on crashes. A driver’s ability to recover from entering a pavement edge drop-off is related to the shape and height of the edge drop and availability of recovery area. As the height of the edge drop-off increases, the driver’s ability to recover decreases. Maintenance standards for edge drop-off vary across jurisdictions, according to factors such as road classification, traffic volume and pavement width by road and shoulder type. Providing a smooth recovery area, including smooth pavement edges, will increase a driver’s ability to regain control of the vehicle (Neuman et al. 2008).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Figure 3.30: Examples of uneven pavement edge drop-off

Source: BP Bitumen (2012).

Methods to improve the edge drop-off include:

 installing a wedge at 30–35 degrees to flatten the slope  adding channelling devices along the elevated side of the drop-off to prevent vehicles travelling beyond this point (Neuman et al. 2008). Maintenance procedures should also be reviewed to ensure that pavement edge deterioration is identified and treated in a timely manner. To improve driver awareness of the edge drop-off it may be beneficial to provide additional pavement markers to delineate the pavement edge (Neuman et al. 2008).

Crash modification An extensive literature search has failed to identify any literature identifying crash modification factors for this treatment. It is recommended that such investigations be conducted in the future.

Treatment life CMF Clearinghouse (2015) recommends a treatment life of seven years for edge treatments.

3.9.4 Median Shoulder A paved median shoulder (Figure 3.31) allows drivers to regain control of an errant vehicle under more controlled conditions. This reduces the chances that drivers may overcorrect their vehicle leading to a loss of control (Neuman et al. 2008). Harwood et al. (2014) highlight that road agencies may be reluctant to install wider median shoulders so as to encourage vehicles to make emergency stops at the roadside shoulder instead. However, widening medians has been shown to reduce the overall crash rate. A matrix of CMFs is provided in Table 3.6. There may be benefit in widening shoulders as a crash reduction treatment, or in cases where loss-of-control crashes are more likely.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Figure 3.31: Example of paved median shoulder on highway

© 2015 Google Source: Google Maps (2015), ‘New South Wales’, map data, Google, California, USA.

Crash modification Crash modification factors for various median shoulder widths on freeways are shown in Table 3.6. Table 3.6:

CMFs for varying the median shoulder width on freeways Inside shoulder width (m) (after)

Inside shoulder width (m) (before)

0.6

0.6 1.2 1.8 2.4 3.0 3.7

1.00 1.03 1.07 1.11 1.15 1.19

0.6 1.2 1.8 2.4 3.0 3.7

1.00 1.03 1.06 1.10 1.13 1.17

1.2

1.8

Fatal and injury crashes 0.97 0.93 1.00 0.97 1.03 1.00 1.07 1.03 1.11 1.07 1.15 1.11 Property damage only crashes 0.97 0.94 1.00 0.97 1.03 1.00 1.06 1.03 1.10 1.06 1.13 1.10

2.4

3.0

3.7

0.90 0.93 0.97 1.00 1.03 1.07

0.87 0.90 0.93 0.97 1.00 1.03

0.84 0.87 0.90 0.93 0.97 1.00

0.91 0.94 0.97 1.00 1.03 1.06

0.88 0.91 0.94 0.97 1.00 1.03

0.86 0.88 0.91 0.94 0.97 1.00

Source: Adapted from Harwood et al. (2014).

Treatment life CMF Clearinghouse (2015) indicates that treatments to widen or improve shoulders should have a treatment life of 10–20 years.

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3.10 Median Glare Treatments Glare is defined as an increased amount of brightness in the visual field, to an extent that it is much greater than the luminance the eyes are adapted for, which in turn may cause discomfort or limit visual performance (Bagui, Ghosh & Jha 2004). Glare from the headlights of opposing vehicles can cause drivers to become disorientated and/or lose control of their vehicle, which can include veering towards the opposing lane. There are a variety of antiglare screens available for use, including concrete barriers, fencing, mesh, fabric and tree plantations. A glare screen height of 1.8 m is recommended to provide antiglare protection for drivers in a range of vehicles (Bagui & Ghosh 2009). Antiglare screens (Figure 3.32) can be considered when headlight glare from opposing traffic cannot be controlled through other means, such as sufficient separation between opposing lanes, either laterally or vertically, or through the use of guardrails higher than 700 mm (Bagui, Ghosh & Jha 2004). Figure 3.32: Antiglare screens (see Section 1.6)

Source: ARRB Group.

Crash modification An extensive literature search has failed to identify any literature identifying crash modification factors for this treatment. It is recommended that such investigations be conducted in the future.

Treatment life CMF Clearinghouse (2015) recommends a 10–20 year treatment life for the installation of anti-glare screens.

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3.11 Median Plantations Median plantations (Figure 3.33) can provide a visual and physical separation of opposing traffic. Additionally, they serve as a shield from headlight glare (Bagui, Ghosh & Jha 2004). Figure 3.33: Median plantation

Source: ARRB Group.

Median plantations should be continuous to prevent intermittent dazzling of drivers from glare (Bagui & Ghosh 2009). Median plantations serve a number of functions:

    

visually and physically separate opposing traffic streams delineate road alignment shield drivers from glare (see Section 3.10) enhance aesthetics of roadway maintain driver interest by varying the landscaping (Bagui & Ghosh 2009).

Trees used in the median should be able to thrive in the local environment with minimal maintenance and not grow to a large enough diameter to pose a hazard to motorists (Hallenbeck et al. 2013). Generally, trees with a diameter of under 100 mm (once fully grown) are considered appropriate (Turner & Mansfield 1990). When including plantations in medians, consideration should be given to the maintenance requirements of the median, including safety of road users and maintenance crew during maintenance, and the potential for the plantations to present any visual obstructions as they grow.

Crash modification Moore and Cutler (1992) did not find any significant changes in cross-median crash rates from the installation of median plantations. However, more recently Hallenbeck et al. (2013) have demonstrated an overall crash reduction after unprotected trees were planted in medians.

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Sullivan (2003) found a statistical increase in fatal and injury crashes following the installation of large trees (with a diameter greater than 100 mm) in medians. Therefore, it is suggested that median landscaping should only include trees with trunks that do not exceed 100 mm in diameter once fully grown.

Treatment life An extensive literature search has failed to yield any appropriate values for the service life of landscaping medians. In the absence of any such literature, the 15-year service life for ‘upgrade median’, adopted by CMF Clearinghouse (2015) has been assumed.

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4. Other Road Infrastructure Solutions 4.1

Speed Management

Speed is a major factor in the incidence and severity of road crashes, including head-on crashes. Head-on crashes are the third most common crash type for speed-related rural crashes in Australia, and the second most common in New Zealand (Austroads 2010c). Central to the Safe System approach is management of vehicle speeds to ensure that those crashes that do occur happen at survivable impact speeds. As a pillar of a Safe System, speed management (safer speeds) should be considered as a means for reducing head-on crash incidence and severity. There are a number of options available for managing speed, many of which are discussed in Austroads (2014c).

Crash modification Whilst there are a range of methods available to reduce travel speeds based on the environment, as an indication, Jaarsma et al. (2011) indicates that reducing speed limits from 80 km/h to 60 km/h on minor rural areas can reduce head-on crashes by 20% (CMF of 0.80).

Treatment life Whilst there are a range of methods available to reduce travel speeds based on the environment, as an indication, signage to encourage lower speeds has a nominal treatment life of ten years (Austroads 2010f).

4.2

Intermittent Overtaking Lanes

Intermittent overtaking lanes provide motorists with opportunities to overtake slower-moving vehicles without moving into the opposing traffic lane. This helps to reduce poor overtaking choices resulting from frustration or impatience. As such, this treatment can help reduce overtaking-related head-on crashes (Neuman et al. 2003). Also, by providing an additional lane between the general (non-overtaking) flow of traffic in both directions, the overtaking lane provides a buffer between most traffic, helping to reduce head-on crashes involving errant vehicles (Neuman et al. 2003). Such a treatment may involve some construction work to install an additional lane, and therefore incurs both cost, construction time and ongoing maintenance. However, as the resulting layout is only three lanes wide, it requires less resources to implement than converting the roadway to a four-lane road, whilst also providing for frequent overtaking opportunities (Neuman et al. 2003). As well as its 2+1 road layout with WRMBs (Section 3.6.4), Sweden has also adopted 2+1 road configurations without WRMBs. Instead of WRMBs, painted medians are used to divide traffic. This system is used on roads with a maximum speed limit of 90 km/h, and has reduced FSI crashes by 40% (Carlsson 2009). Jaehrig (2014) has demonstrated that even passing lanes as short as 0.6–1.2 km are long enough to reduce the pressure on overtaking (for road sections with AADT of 5 000–10 000 vpd). This may be an effective countermeasure when there are constraints preventing more wide-scale implementation of passing lanes. Care needs to be taken as the short overtaking distances encourage overtaking drivers to travel faster. This has not been found to affect the safety of the road, but such overtaking lanes should not be positioned close to intersections (Jaehrig 2014). Such overtaking lanes may be of particular benefit on steep inclines, where slower vehicles are more common, and on roads with limited sight distance, where drivers may otherwise begin overtaking manoeuvres unaware of approaching traffic.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Figure 4.1:

Roadway featuring intermittent overtaking lanes

Source: ARRB Group.

Crash modification Roads and Maritime (2015b) suggests that intermittent passing lanes can reduce head-on crashes by 25% (CMF of 0.75). The reductions in fatal and serious injury crashes are not as significant as 2+1 roads with WRMBs, being about half that of the latter. However, compared against standard 13 m wide roads, FSI crash rates for intermittent overtaking lanes without a median barrier were reduced by almost 40% (CMF of 0.60) (Carlsson 2009). An expert panel commission by the US National Cooperative Highway Research Program (NCHRP) determined that intermittent passing lanes on two-way, two-lane rural roads in one direction would lead to a 25% reduction in all crashes (CMF of 0.75). Where passing lanes are added to both directions of traffic, a 35% reduction (CMF of 0.65) is expected (Niessner 2005; Harkey et al. 2008). These modification factors exclude any crash reduction taking place upstream or downstream of the site. It might be presumed that there would be a crash reduction upstream and downstream of an area where an overtaking lane has been applied, as drivers are encouraged to wait for safer opportunities to overtake (Niessner 2005; Harkey et al. 2008; Carlsson 2009). Considering upstream and downstream crashes as well as crashes at overtaking lanes, Bagdade et al. (2011) indicate negligible change to total crashes (CMF of 1.00), but a 40% reduction in injury crashes (CMF of 0.60). Considering target crashes only (head-on crashes included), the treatment resulted in a crash reduction of 45% (CMF of 0.55). It has been found that even short overtaking lanes, 0.6–1.2 km long, provided at least every 4 km, can reduce FSI crashes related to overtaking by 65% (CMF of 0.35) (Jaehrig 2014). Austroads (2010d) indicates a total crash reduction of 25% (CMF of 0.75) with the provision of overtaking lanes.

Treatment life CMF Clearinghouse (2015) recommends a treatment life of 15 years for the installation of overtaking lanes.

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4.3

Improved Pavement Surface

In 2001 in the US, 13% of cross-median crashes on interstate roads were due to wet surfaces, and a further 4% to roadways affected by snow and ice. A high number of wet weather crashes can be indicative of crashes where the pavement’s skid resistance is a factor. By improving the level of skid resistance at a location, the incidence of loss-of-control crashes in wet conditions would reasonably be expected to fall (Neuman et al. 2008). High-friction pavement treatments are most typically used at locations where hard braking may be required, e.g. on downgrades or approaching a crossing or perhaps sharp curves. These treatments are generally only effective on road surfaces that initially have a coefficient of friction below 0.7 (Harwood et al. 2014).

Crash modification When applied at appropriate locations, improving the pavement surface can reduce total crash rate by 5–10% (CMF of 0.90–0.95), entirely due to a reduction in wet and snowy weather related crashes (Harwood et al. 2014). Roads and Maritime (2015b) have adopted a head-on CRF of 35% (CMF of 0.65) for head-on crashes in wet weather.

Treatment life CMF Clearinghouse (2015) indicates a service life of five years for high friction surface treatments. General improvements for pavement friction can have a surface life of ten years.

4.4

Shoulder Treatments

Head-on crashes may result from drivers overcorrecting after drifting to the side of the road. By widening and sealing shoulders, drivers are given more space to correct their vehicle path (Austroads 2010e).

Crash modification Austroads (2009c) indicates a 40% reduction in head-on crashes (CMF of 0.60) from the sealing of shoulders. Emer et al. (1991) in Austroads (2010e) indicate a 10% reduction in head-on crashes from shoulder construction (CMF of 0.90) and a 20% reduction in head-on crashes from shoulder repairs (CMF of 0.80). The Land Transport Safety Authority (1995) in Austroads (2010e) indicate a 45% reduction in head-on crashes (CMF of 0.55) when shoulder improvements are made at crash blackspots on bends. Gan, Shen and Rodriguez (2005) indicate a 45% reduction in head-on crashes from widening a paved shoulder (CMF of 0.55) and a 30% reduction in all crashes (CMF of 0.70).

Treatment life CMF Clearinghouse (2015) recommends a service life of 10–20 years for treatments that improve or widen the shoulder.

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4.5

Improved Roadside Forgiveness

Austroads (2014a) reported that head-on crashes appear to be higher on roads featuring an unforgiving roadside environment. Roadsides that appear unforgiving or give the impression of being very close to the roadway may encourage drivers to travel closer to the centre of the road than they otherwise might. This reduces the clearance between opposing traffic, and hence can increase the incidence of head-on crashes. In response, obvious roadside hazards should be removed, relocated further from the roadway or shielded. If roadside hazards are replaced by frangible items, these items should be visibly more forgiving, so that drivers feel more comfortable travelling closer to them.

Crash modification An extensive literature review has failed to identify any specific crash modification factors for improvements to the roadside. It would be informative to undertake research as to the relationship between roadside forgiveness and head-on crash rates.

Treatment life Treatment life will vary based on the treatments required to improve roadside forgiveness. As a guide, CMF Clearinghouse (2015) recommends a treatment life of 10–20 years to relocate or remove fixed objects.

4.6

Curve Delineation and Warning

It is important that drivers set up for, and enter, curves at an appropriate speed in order to maintain control of their vehicle. Without appropriate delineation to assist the driver, the driver may approach at too high speed, or enter the curve along an inappropriate path, which may result in the vehicle crossing into oncoming traffic. To warn and inform drivers of approaching curves, warning signs, speed advisory signs, chevron boards, curve alignment markers (CAMs) and guideposts have all been traditionally used (Austroads 2010e). More recently, vehicle activated signs have been designed to be used on the approach to curves to attract greater attention from drivers to advise them to reduce travel speeds. These may be set to activate for a short time when an approaching vehicle is exceeding a set threshold speed. IIPMs, discussed in Section 2.6, are also an option to provide enhanced night-time delineation where curve alignment will not permit headlights to adequately illuminate RRPMs. Figure 4.2 and Figure 4.3 show examples of curve delineation and warning treatments. Further information on curve delineation and warning methods can be found in Austroads (2014c).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Figure 4.2:

Delineation of curve with CAMs

Source: ARRB Group. Figure 4.3:

Delineation and warning of curve with vehicle activated signage and chevron board

Source: TMR, private communication, February 2015.

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Crash modification Roads and Maritime (2015b) has adopted the following relevant head-on crash reduction factors:

   

CAMs: 20% (CMF of 0.80) curve warning signs: 25% (CMF of 0.75) guideposts: 10% (CMF of 0.90) vehicle activated signs: 15% (CMF of 0.85).

Table 4.1 summarises various treatments available and their associated safety benefits as sourced from Austroads (2010e). Table 4.1:

Summary of various curve delineation treatments and respective crash reduction and modification factors

Treatment type

Crash category

Crash reduction

Crash modification factor

Head-on

75%

0.25

All

50%

0.50

Daytime

40%

0.60

Night-time

55%

0.45

Lane departure (including head-on)

20%

0.80

Curve warning signs

All

30%

0.70

Guide posts

All

20%

0.80

Vehicle activated signs

All

30%

0.70

CAMs

Improved curve delineation

Source: Austroads (2010e).

Treatment life The following service lives for various options of treatment methods are suggested:

 10 years for signage (warning signs, curve alignment markers, etc.) and posts that may be used to warn and inform drivers of curves (Austroads 2010f)

 3–5 years for improved delineation (Austroads 2010f)  5–10 years for vehicle activated signs (Austroads 2014c).

4.7

Addressing Wrong-way Movements

Some head-on crashes are a result of drivers mistakenly driving on the wrong side of a road or freeway. Whilst such crashes are generally less common, they are more likely to result in fatal and serious injury outcomes (Neuman et al. 2008). Wrong-way related crashes most frequently originate at freeway exit ramps (i.e. when a driver enters the freeway via the exit ramp), and are more common during night-time, particularly during the early morning hours (Cooner, Cothron & Ranft 2004). Figure 4.4 shows signage used in the Barossa Valley in South Australia. Due to the high number of foreign visitors on the road, signage such as this is included near stopping bays and along re-entry points to the scenic drive to remind foreign drivers to travel on the correct side of the road, and thus avoid entering the lane of opposing traffic.

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Figure 4.4:

‘Drive on left in Australia’ signage used in the Barossa Valley

Source: Orderinchaos (2014).

‘Wrong way/go back’ signs may also be used at exits to motorways, facing away from the correct travel stream, so any drivers mistakenly entering via the exit are aware to turn around to avoid a crash (Figure 4.5). In order to improve the visibility of these signs, the following treatments may be considered (Morena & Leix 2012; Zhou & Rouholamin 2014):

    

lower placement of signs below the standard to ensure they are at driver’s eye height

      

installation of wrong-way pavement marking arrows

use of oversized signs reflective sheeting on the sign supports enhancement of signs with LEDs position of STOP bars on the exit ramps as a cue that the exit ramp is intended only for traffic leaving the freeway installation of pavement marking extensions guiding traffic past the exit ramp and onto the entrance ramp delineation of traffic island to highlight the separation between the lamps multiple signs on same post inclusion of FREEWAY ENTRANCE signs for all on ramps reflective pavement markers shining red for wrong way traffic red delineator installed on guardrail along exit ramp, facing wrong way traffic.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Figure 4.5:

Wrong way/go back signage at motorway exit (inset shows greater detail)

© 2015 Google Source: Google Maps (2015), ‘New South Wales’, map data, Google, California, USA.

Crash modification It appears that, due to the low number of such crash scenarios, no literature has been found discussing the crash reductions resulting from treatments to address wrong-way movements. However, due to their likely high severity, it is still important to address wrong-way movements where there is an increased likelihood of such dangerous actions.

Treatment life There are a number of methods available to address wrong-side-of-road driving. As a guide, the following service lives for various treatment options are suggested:

 10 years for relevant signage (Austroads 2010f)  3–5 years for pavement markings delineation (Austroads 2010f)  5 years for RRPMs (Austroads 2014c).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

5. Conclusion The primary objective of this report is to present an overview of median and centreline treatments to reduce head-on crashes. However, this report also introduces the road safety practitioner to other methods available to treat head-on crashes. The report provides information on well-proven treatments and methods in addressing head-on crashes, including any issues associated with their implementation that should be considered prior to their adoption. This report has also presented some innovative treatments – many of which have yet to be formally evaluated, i.e. there is currently insufficient data to confirm their benefits. Nonetheless, these methods are expected to address head-on crashes, and may be of benefit in situations where the crash history site does not justify the expense associated with more established treatments. Appendix A summarises the road engineering based treatments discussed in this report, including an indication of their likely performance (stated in the form of crash modification factors), and typical characteristics that may inform the decision to adopt this treatment. Where information is lacking or not yet available, the table also identifies areas of research that could benefit understanding of road safety solutions. It is important to note that the table is an overview only, and the reader is advised to refer to the in-text details for greater detail. The reader is also advised to consult with the relevant jurisdiction for the crash modification factors, costs and treatment lives used for local cost-benefit analysis methods, as well as any specific policies or design specifications pertaining to that treatment for the jurisdiction. Consultation with manufacturers is also recommended in order to determine any product-specific requirements.

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Harkey, DL, Srinivasan, R, Baek, J, Council, FM, Eccles, K, Lefler, N, Gross, F, Persaud, B, Lyon, C, Hauer, E & Bonneson, JA 2008, Accident modification factors for traffic engineering and ITS improvements, NCHRP report no. 617, National Cooperative Highway Research Program, Transportation Research Board, Washington, DC, USA. Harwood, DW, Gilmore, DK, Graham, JL, O’Laughlin, MK, Smiley, AM & Smahel, TP 2014, Factors contributing to median encroachments and cross-median crashes, NCHRP report 790, Transportation Research Board, Washington, DC, USA. Haynes, R 2009, ‘Frustrated drivers allegedly use median strip on The Norwest Boulevard, Glenwood’, Daily Telegraph, 22 September 2009, viewed 24 March 2016, . Highway Engineering in Australia 2008, ‘Intelligent road studs: improve safety and visibility on rural roads’, Highway Engineering in Australia, vol. 40, no. 3, pp. 10. Hirasawa, M, Tetsuya, T, Motoki, A & Kazuo, S 2006, ‘Developing optimal centerline rumble strips and evaluating their safety benefits on national highways in Hokkaido, Japan’, Transportation Research Board annual meeting, 85th, 2006, Washington, DC, TRB, Washington, DC, USA, 15 pp. Høye, A 2011, ‘The effects of electronic stability control (ESC) on crashes: an update’, Accident Analysis & Prevention, vol. 43, no. 3, pp. 1148-59. Ingal Civil 2015a, Stack cushion, Ingal Civil, Minto, NSW, viewed 24 March 2016, . Ingal Civil 2015b, Ingal rub rail, Ingal Civil, Minto, NSW, viewed 24 March 2016, . Insurance Institute for Highway Safety 2012, Status report – Lane departure warning, vol. 47, no. 5. Insurance Institute for Highway Safety 2014, Status report – Quick work Better autobrake helps more models earn top ratings for front crash prevention, vol. 49, no. 4. Jaarsma, R, Louwerse, R, Dijkstra, A, de Vries, J & Spaas, J 2011, ‘Making minor rural road networks safer: the effects of 60 km/h-zones’, Accident Analysis & Prevention, vol. 43, no. 4, pp. 1508-15. Jaehrig, T 2014, ‘Safe passing as a measure to improve road safety on rural roads in Germany’, ARRB conference, 26th, 2014, Sydney, NSW, ARRB Group, Vermont South, Vic, 13 pp. Jama, HH, Grzebieta, RH, Friswell, R & McIntosh, AS 2011, ‘Characteristics of fatal motorcycle crashes into roadside safety barriers in Australia and New Zealand’, Accident Analysis & Prevention, vol. 43, no. 3, pp. 652–60. Jamieson, N, Frith, W, Lester, T & Dravitzki, V 2013, Stability of motorcycles on audio tactile profiled (ATP) roadmarkings, NZ Transport Agency research report 526, NZ Transport Agency, Wellington, NZ. Kar, K & Weeks, RS 2009, ‘Centerline rumble strips for reducing lane departure crashes’, Accident Reconstruction Journal, vol. 19, no. 4, pp. 33-5. Lambert, J & Rechnitzer, G 2002, Review of truck safety: stage 1: frontal, side and rear underrun protection, report 194, Monash University Accident Research Centre, Clayton, Vic. Levett, SP, Job, RFS & Tang, J 2009, ‘Centreline treatment countermeasures to address crossover crashes’, Australasian road safety research policing education conference, 2009, Sydney, NSW, Roads and Traffic Authority, Sydney, NSW, 14 pp. Lilley, M 2012, ‘The NZ Transport Agency Highways And Network Operations Traffic Control Devices trials updated’, Australasian road safety research policing education conference, 2012, Wellington, New Zealand, Ministry of Transport, Wellington, NZ, 8 pp.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Lyon, C, Persaud, B & Eccles, K 2015, Safety evaluation of centerline plus shoulder rumble strips, report FHWA-HRT-15-048, Federal Highway Administration, McLean, Virginia, USA. Mackie, H, Marsh, F & Pilgrim, M 2011, ‘Do ‘safe-hit’ post medians have a place in New Zealand’s safe roads system?’, Institution of Professional Engineers New Zealand (IPENZ) transportation conference, 2011, Auckland, New Zealand, Harding Consultants, Christchurch, NZ, 12 pp. Main Roads Western Australia 2014, Design of kerbing, MRWA, Perth, WA, viewed 24 March 2016, . Marsh, F & Pilgrim, M 2010, ‘Evaluation of narrow median wire rope barrier installation on Centennial Highway, New Zealand’, Journal of the Australasian College of Road Safety, vol. 21, no. 2, pp. 34-41. Migletz, J & Graham, J 2002, Long-term pavement marking practices: a synthesis of highway practice, NCHRP synthesis 306, Transportation Research Board, Washington, DC, USA. Ministry of Transport 2015, Electronic stability control, Ministry of Transport, Wellington, New Zealand, viewed 24 March 2016, . Morena, DA & Leix, TJ 2012, ‘Strategies to curtail wrong-way crashes on freeways’, Accident Reconstruction Journal, vol. 22, no. 4, pp. 29-34. Moore, R & Cutler, CD 1992, ‘The effect of plantations on median accidents’, report CALTRANS-TO-92-2, California Department of Transportation (Caltrans), Sacramento, CA, USA. National Highway Traffic Safety Administration 2011, Countermeasures that work: a highway safety countermeasure guide for state highway safety offices, 6th edn, report DOT HS 811 444, NHTSA, Washington, DC, USA. Neuman, TR, Pfefer, R, Slack, KL, Hardy, KK, McGee, H, Prothe, L, Eccles, K & Council, F 2003, Guidance for implementation of the AASHTO strategic highway safety plan: volume 4: a guide for addressing headon collisions, NCHRP report no. 500, National Cooperative Highway Research Program, Transportation Research Board, Washington, DC, USA. Neuman, TR, Nitzel, JJ, Antonucci, N, Nevill, S & Stein, W 2008, Guidance for implementation of the AASHTO strategic highway safety plan: volume 20: a guide for addressing head-on crashes on freeways, NCHRP report no. 500, National Cooperative Highway Research Program, Transportation Research Board, Washington, DC, USA. Nilsson, K & Prior, N 2004, ‘Wire rope safety barriers and the Pacific Highway program: RTA research and investigations’, Road safety research, policing and education conference, 2004, Perth, Western Australia, Road Safety Council of Western Australia, Perth, WA, vol. 2, 10 pp. Niessner, CW 2005, Crash reduction factors for traffic engineering and intelligent transportation system (ITS) improvements: state-of-knowledge report, Research Results Digest 299, National Cooperative Highway Research Program, Washington, DC, USA. Olsen, AN, Schultz, GG, Thurgood, DJ & Reese, CS 2011, ‘Hierarchical Bayesian modeling for before and after studies’, Transportation Research Board annual meeting, 90th, 2011, Washington, DC, TRB, Washington, DC, USA, 16 pp. Olson, D, Sujka, M & Manchas, B 2013, Performance analysis of centerline and shoulder rumble strips installed in combination in Washington State, report WA-RD 799.1, Washington State Department of Transportation, Olympia, WA, USA. Orderinchaos 2014, Drive on Left in Australia, sign at Bethany, SA, Wikimedia Commons, viewed 24 March 2016, . Partridge, R 2015, ‘No room for a median treatment? Think again’, Institution of Professional Engineers New Zealand (IPENZ) transportation conference, 2015, Christchurch, New Zealand, Institution of Professional Engineers New Zealand, Wellington, NZ, 7 pp.

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Persaud, BN, Retting, RA & Lyon, CA 2004, ‘Crash reduction following installation of centerline rumble strips on rural two-lane roads’, Accident Analysis & Prevention, vol. 36, no. 6, pp. 1073-9. Roads and Traffic Authority 2010, Delineation: section 16: guide posts and delineation of safety barriers, Roads and Traffic Authority, North Sydney, NSW. Roads and Maritime Services 2015a, Road users’ handbook, Roads and Maritime, Sydney, NSW. Roads and Maritime Services 2015b, Nomination form for councils, Roads and Maritime, viewed 24 March 2016, . Ross, HE, Sicking, DL, Zimmer, RA & Michie, JD 1993, Recommended procedures for the safety performance evaluation of highway features, NCHRP report 350, Transportation Research Board, Washington, DC, USA. Sayed, T, deLeur, P & Pump, J 2010, ‘Impact of rumble strips on collision reduction on highways in British Columbia, Canada: comprehensive before-and-after safety study’, Transportation Research Record, no. 2148, pp. 9-15. Schultz, GG, Thurgood, DJ, Olsen, AN & Reese, CS 2011, ‘Analyzing raised median safety impacts using Bayesian methods’, Transportation Research Record, no. 2223, pp. 96-103. Smadi, O, Hawkins, N, Nlenanya, I & Aldemir-Bektas, B 2010, Pavement markings and safety, report IHRB Project TR-580, Iowa Department of Transportation, Ames, IA, USA. Stine, JS, Hamblin, BS, Brennan, SN & Donnell, ET 2010, ‘Analyzing the influence of median cross-section design on highway safety using vehicle dynamics simulations’, Accident Analysis & Prevention, vol. 42, no. 6, pp. 1769-77. Styles, T, Cairney, P, Studwick, G & Purtill, S 2003, ‘Trial and evaluations of internally illuminated pavement markers’, Road Safety Research, Policing and Education Conference, 2003, Sydney, NSW, Roads and Traffic Authority, Sydney, NSW, vol. 2, pp. 550-5. Sullivan, EC 2003, Safety of median trees with narrow clearances on urban conventional highways, California Department of Transportation (Caltrans), Sacramento, CA, USA. Tarko, AP, Villwock, NM & Blond, N 2008, ‘Effect of median design on rural freeway safety: flush medians with concrete barriers and depressed medians’, Transportation Research Record, no. 2060, pp. 29-37. Torbic, DJ, Hutton, JM, Bokenkroger, CD, Bauer, KM, Harwood, DW, Gilmore, DK, Dunn, JM, Ronchetto, JJ, Donnell, ET, Sommer, HJ, Garvey, P, Persaud, B & Lyon, C 2009, Guidance for the design and application of shoulder and centerline rumble strips, NCHRP report no. 641, National Cooperative Highway Research Program, Transportation Research Board, Washington, DC, USA. Traffic Technology Today 2014, Germany trials green markings on three-lane highways, Traffic Technology Today, viewed 24 March 2016, . Transport Canada 2013, Electronic stability control, Transport Canada, Ottawa, Ontario, viewed 24 March 2016, . Transport for NSW 2012, Head-on crashes with heavy vehicles: relevance of safety barriers, report TSR 12/01, TfNSW, Chippendale, NSW. Turner, D & Mansfield, E 1990, ‘Urban trees and roadside safety’, Journal of Transportation Engineering, vol. 116, no. 1, pp. 90-104. VicRoads 2005, Use and operation of internally illuminated pavement markers, Traffic Management Note no. 20, VicRoads, Kew, Vic. VicRoads 2014, Traffic engineering manual volume 2 chapter 15: pavement markings, 5th edn,, VicRoads, Kew, Vic.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Villwock, N, Blond, N & Tarko, AP 2009, ‘Safety impact of cable barriers on rural interstates’, Transportation Research Board annual meeting, 88th, Washington, DC, TRB, Washington, DC, USA. Volvo Trucks Australia 2011, The new Volvo FE Euro 5, Volvo Trucks Australia, Wacol, QLD, viewed 24 March 2016, . Whittaker, A 2012, ‘The safety benefit of continuous narrow painted median strips: continuous narrow painted median trial: preliminary findings’, Department of Transport and Main Roads, Brisbane, QLD. World Highways 2015, ‘The moveable barrier’s time has arrived’, The Global Road Safety Review 2015, World Highways, Kent, UK. Zhou, H & Rouholamin, MP (eds) 2014, Proceedings of the 2013 national wrong-way driving summit, report FHWA-ICT-14-009, Illinois Department of Transportation, Springfield, IL, USA. Standards Australia AS/NZS 3845.1:2015, Road safety barriers systems and devices part 1: road safety barrier systems. AS 1742.2-2009, Manual of uniform traffic control devices part 2: traffic control devices for general use.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Summary of Treatments Most effective at reducing crash:

Range for: Treatment

Centreline

Crash reduction factors

Crash modification factors

Head-on: 15%

0.85

Standard (all): 30%

0.70

No-overtaking zone (all): 35%

0.65

Raised profile Head-on: 20–55% 0.45–0.80 centrelines FSI head-on: 25–65% 0.35–0.75 All: 10–15%

0.85–0.90

All FSI: 10–30%

0.70–0.90

Raised profile Head-on: 35–65% centreline FSI head-on: 30% and Lane departure: edgelines 20–65%

Indicative cost(1)

3

$400–$5 000/km

5

$1 000–$9 000/km



 Appropriate along no-overtaking zones  Most effective at addressing fatigue-related or distractionrelated loss-of-control crashes, including head-on crashes  Consideration should be given to noise levels in urban areas

5

$3 000–$14 000/km



 Suitable where insufficient warrants for raised profile centrelines

5

$2 500–$17 500/km

3

$2 500/km

Incidence Severity



 On rural roads, AADT over 300 vpd  On urban roads, AADT over 2500 vpd  Curve/crest profile may warrant centrelines on lower volume roads



 Appropriate along no-overtaking zones  Most effective at addressing fatigue-related or distractionrelated head-on crashes  Consideration should be given to noise levels in urban areas

0.35–0.65 0.70 0.35–0.80

FSI lane departure: 45%

0.55

All: 20%

0.80

Profiled All night-time: 10– thermoplastic 15% stripes

0.85–0.90

Road marking tape

0.85–0.90

All night-time: 10– 15%

Typical treatment life (years)

Typical road characteristics



 For treatments requiring minimal markings to perform under severe conditions

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Most effective at reducing crash:

Range for: Treatment

RRPMs

IIPMs

Crash reduction factors

Crash modification factors

Head-on: 15%

0.85

All: 5%

0.95

All night-time dry: 10%

0.90

All night-time wet: 20%

0.80

Typical treatment life (years)

Indicative cost(1)

5

$600/km

 For use where alignment does not permit adequate headlight illumination of RRPMs  For use where night-time delineation over long distances is required

5

$2 000/km

 Too narrow for raised median  Minimum width of 0.6 m, ideal minimum width of 1.0 m  Care should be taken to prevent drivers treating median as a transit lane

5

$12 000/km



 85th percentile speed below 75 km/h only  Useful substitute when raised medians unsuitable (narrow width, drainage issues)

5

$25–$90 per unit



 1.0 m width  Appropriate for roads as narrow as 7 m (lanes of 3 m width)

3–5

$14 000–$35 000/km



 For speed zones greater than 60 km/h  Minimum length of 10 m at 60 km/h to 40 m at 100 km/h  Care should be taken to prevent drivers treating median as a transit lane

20

$110–$300/m2

30

$50 000–$70 000/km

Typical road characteristics Incidence Severity  As augmentation of centrelines wherever appropriate 

No findings available 

Painted median

Head-on: 40%

0.60

All: 15–20%

0.80–0.85 

Pavement bars

No findings available

Wide centreline treatment

Head-on: 50–80% All: 60%

0.40

Raised median

Head-on: 60%

0.40

All: 40–55%

0.45–0.60

All FSI: 45%

0.55

0.20–0.50

Barrier kerbing

No findings available

Median barriers

All: –25%

1.25

All Injury: 30%

0.70

All fatal: 45%

0.55

 For speed zones less than 70 km/h





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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Most effective at reducing crash:

Range for: Treatment Crash reduction factors Rigid median Head-on: 100% barriers Single vehicle: 120%

Semi-rigid median barriers

Wire rope median safety barriers

Crash modification factors

Typical treatment life (years)

Indicative cost(1)

30

$400 000– $500 000/km



 Not on inside of very tight curves  Either within 200 mm from kerb or separated significantly from it  Minimum length of 30 m

30

$110 000– $200 000/km



30

$110 000– $350 000/km

30

$150 000– $400 000/km

Indefinite (with refurbishment)

None provided

Typical road characteristics Incidence Severity

0.0 2.2



 Offset 1–3 m from edge of lane (no more than 4 m)  Minimum length of 20–30 m

Injury: –15–10%

0.90–1.15

Fatal: 90%

0.10

Head-on: 95%

0.05

Head-on (cars): 98%

0.02

Head-on (trucks): 75–90%

0.10–0.25

Head-on: 60–95%

0.05–0.40

Single vehicle: –40 to –95%

1.40–1.95

All FSI: 0–75%

0.25–1.00

 Lateral slope < 10:1  Tension not affected by horizontal or vertical radius  Sufficient displacement from other barriers and hazards for deflection

0.20

 13 m cross-section

2+1 road with All fatal: 80% WRMB Motorcycle FSI: 40–50%

0.50–0.60

Fatal (110 km/h): 75% 0.25 Fatal (90 km/h): 80%

0.20

Severe injury: 55%

0.45

Moveable barriers

Assumed as for rigid barriers

Flexible bollards

No findings available

Median turning bays

Head-on: 35%

0.65

All: 30%

0.70

Widen median

Head-on: 0–75%

0.25–1.00

All: 0–50%

0.50–1.00







 As ford rigid barriers, but on locations where tidal flow is required during peak periods



 Where installations of wire rope barrier not justified by crash history

30

$50–$250 per unit



 At intersections with history of rear-end as well as head-on crashes

7–20

$10 000/km

5–20

$100–$400/m2



 Should not be used on roads that are prone to congestion

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Most effective at reducing crash:

Range for: Treatment Crash reduction factors Median Head-on: 20% cross-section

Crash modification factors 0.80

Pavement No findings available edge drop-off

Typical road characteristics Incidence Severity  Trapezoidal median cross-sections have lower head-on incidence than v-ditch cross-sections



 Traversable median edge allows recovery of errant vehicle



Typical treatment life (years)

Indicative cost(1)

10–20

$750 000/km

7

$20 000–$80 000/km



 Care not to encourage drivers to treat median shoulder as break down area

10–20

$50–$100/m2

No findings available



 For use when road geometry promotes opposing headlight glare that is not blocked by median barrier

10

$100 000– $500 000/km

Low to negligible



 Tree trunks should not exceed 100 mm diameter once fully grown

15

$300 per tree

 For use where high speeds (legal or illegal) are a factor in head-on crash occurrence

10

$1 000/km

15

$50 000/km

Median shoulder

FSI: 0–15%

Median glare treatments Median plantations

0.85–1.00

Speed Head-on (from 80 to management 60 km/h): 20%

0.80

Intermittent overtaking lanes

Head-on: 25%

0.75

Target crashes: 45%

0.55

All FSI: 40%–65%

0.35–0.60

All injury: 40%

0.60

All: 25%

0.75

Improved pavement surface

Head-on: 35%

0.56

All:5–10%

0.90–0.95

Shoulder treatments

Head-on: 10–45%

0.55–0.90

All: 30%

0.70

Improved roadside forgiveness

No findings available

Curve delineation/ warning

Head-on: 10–75% All: 20–50%



 Where head-on crashes are associated with unsafe overtaking manoeuvres 



 Wet/snowy environments  Where hard braking required (i.e. downhill gradients or sharp curves)

5–10

$5–$150/m2



 Appropriate shoulders reduce the incidence of drivers of vehicle drifting to the left overcorrecting into oncoming traffic

10–20

$100–$300/m2



 Roadsides that appear more forgiving encourage drivers to travel further from the centreline, increasing the buffer between opposing traffic

10–20

None provided

3–10

$3 500/curve

0.25–0.90 0.50–0.80





 Appropriate where head-on crashes occur on or near curves

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Most effective at reducing crash:

Range for: Treatment Crash reduction factors Addressing wrong-way movements 1

Crash modification factors

Typical road characteristics Incidence Severity

No findings available 

 Roads with high tourist volumes (e.g. nationally significant routes, airport access roads)  Motorway exits

Typical treatment life (years)

Indicative cost(1)

3–10

$4 000/treatment

Costs are a guide only to assist in comparing treatments. Practitioners are advised to consult with their local jurisdiction for more accurate cost estimates when preparing a costbenefit analysis. Costs may vary based on the jurisdiction, project scope, site location and other environmental factors.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Other Countermeasures to Address Head-on Crashes The previous sections of this report have discussed road engineering and speed management techniques to address head-on crashes. Whilst this is the primary focus of this Austroads report, a Safe System approach requires consideration of all four pillars in the travel system to address a safety concern. As such, this section briefly discusses interventions based on the other two remaining pillars in a Safe System, safer road users and vehicles.

B.1

Driver Interventions Fatigue Management

Fatigue has been identified as a contributing factor to head-on crashes. This may be due to travelling long distances (more common in rural environments) and chronic sleep impairment, such as from shift work (more common in urban environments) (Austroads 2014a; Austroads 2010e). Measures to encourage drivers to only drive having had sufficient sleep may be difficult to implement when sleep impairment is a chronic lifestyle issue, such as associated with shift workers. However, work-related fatigued driving may be managed through employer-based policies and programs (National Highway Traffic Safety Administration 2011).

Driver Distraction Driver distraction or inattention is also associated with head-on crashes in urban and rural environments (Austroads 2014a; Austroads 2010e). Measures to encourage drivers to avoid distractions in the car may be difficult as many drivers will consider some distractions as important and common to most drivers, and therefore will not give them up. This is especially difficult as drivers are typically poor judges of the impact of distracting activities on their driving performance (National Highway Traffic Safety Administration 2011).

B.2

Vehicle-based Treatments Front Underrun Protection

In a head-on crash, when passenger cars and trucks have differing heights and geometries, parts of the car may travel under, or ‘underrun’ the truck structure. This is known as ‘vehicle incompatibility’ (Lambert & Rechnitzer 2002). Crashes between passenger vehicles and trucks are generally most severe when occurring head-on, with head-on crashes involving light trucks of only three tonnes (twice the mass of passenger vehicles) at high risk of resulting in fatal or serious injuries, even on urban arterial roads. This is due to both the high kinetic energy transfers resulting from the mass of the truck, and the potential for underrun. As a result, the majority of fatal crashes between passenger vehicles and trucks are head-on crashes (Lambert & Rechnitzer 2002).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

In head-on crashes featuring underrun, any amount of underrun may significantly compromise the crashworthiness of the underrun vehicle. Once underrun occurs, the vehicle’s ability to absorb crash energy is compromised, and there is increased risk of intrusion into the occupant compartment. Considering the high potential severity of head-on crashes with trucks, it is important to maximise the crashworthiness of the vehicles involved, by addressing underrun (Lambert & Rechnitzer 2002). Whilst Lambert and Rechnitzer (2002) recommend front underrun protection for all trucks (see Figure B 1) with a gross vehicle mass (GVM) greater than 3.0 tonnes, the current Vehicle Standard (Australian Design Rule 84/00 – Front Underrun Impact Protection) 2009 only requires front underrun protection for heavy goods with optional compliance for medium goods vehicles with a GVM greater than 4.5 tonnes. Figure B 1:

Truck fitted with front underrun protection (circled)

Source: Volvo Trucks Australia (2011).

Crash modification Penetration of front underrun protection on the heavy vehicle fleet is still low, and as a result, statistical analysis of the benefits of this technology are so far inconclusive (Chislett & Robinson 2010). It should be expected that, by allowing vehicles to maximise their crashworthiness, the severity of any crashes should be lower when front underrun protection is in place. However, considering the high forces involved in head-on crashes with trucks, it is likely that many crashes will continue to result in fatal and serious injuries despite this advance.

Anti-lock Braking Systems Anti-lock braking systems (ABS) are designed to prevent wheel lock-up in braking. ABS detects the onset of wheel lock-up and limits braking pressure to prevent lock-up occurring. ABS will then reapply braking until the onset of wheel lock-up, at which point it releases again. This allows braking efficiency to be close to the maximum possible. Drivers will sense a pulsating effect when ABS is applied as the brakes are constantly applied and released throughout activation (Burton et al. 2004).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

ABS allows for maximum braking efficiency, even on surfaces with poor skid resistance. As a result, drivers should be able to avoid some collisions altogether by bringing their vehicle to a complete stop earlier than otherwise. In other situations where collisions may be unavoidable, with improved braking efficiency, the speed of impact should be lower, thus reducing the severity of impact (Burton et al. 2004). As wheels do not lock up during braking with ABS, the technology also allows for drivers to steer whilst braking (Burton et al. 2004).

Crash modification Burton et al. (2004) report that ABS has been found to reduce the rate of head-on collisions. Studies have shown a reduction in multi-vehicle collisions ranging from 10% to 40% (CMF of 0.60–0.90), with a greater reduction for collisions in wet or slippery conditions.

Electronic Stability Control Electronic stability control (ESC) is designed to avoid loss of control of a vehicle by tracking the vehicle’s steering input and direction of travel. When steering and direction of travel are not corresponding, ESC applies the brakes. To correct oversteer (when the back of the vehicle slides out), either the nearside or offside front brake is applied, depending on the side where there is loss of control. Similarly, for understeer (when the front of the vehicle starts to skid), braking is applied to the nearside or offside rear, depending on the direction of loss of control (Chouinard & Lécuyer 2011) (see Figure B 2). From November 2011, ESC was made mandatory for all new passenger vehicles sold in Australia (Høye 2011). From 1 July 2015, ESC was made mandatory for all new passenger vehicles sold in New Zealand (Ministry of Transport 2015).

Crash modification Burton et al. (2004) and Aga and Okada (2003) both indicate that ESC can reduce the rate of head-on crashes by 30% (CMF of 0.70). This technology is more effective for severe head-on crashes, reducing their incidence by 40% (CMF of 0.60) (Aga & Okada 2003).

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Figure B 2:

Overview of effect of Electronic Stability Control4

Source: Transport Canada (2013).

Lane Departure Warning Lane departure warning systems use sensors or a video camera to detect the position of the lane or edgeline on a road relative to the vehicle’s position. If the line is being approached without a lane change indication being activated, the system alerts the driver (Austroads 2010h). A more advanced version of this technology is lane departure prevention, which will gently steer the vehicle back into its lane if it begins to deviate. This may prove more effective than a warning system that relies on driver input (Insurance Institute for Highway Safety 2012).

Crash modification Austroads (2010h) has provided an estimate, based on manufacturer’s estimates, that this technology would reduce all crashes by about 25% (CMF of 0.75).

4

Note, diagram is sourced from Transport Canada and depicts vehicles travelling on the right-hand side of the road.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Collision Warning and Prevention Systems Collision warning systems use sensors or video cameras to detect whether a collision may be imminent. Passive systems then warn the driver of the collision, and prepare the vehicle’s passive safety systems for a collision (e.g. pretension seatbelts). Active collision prevention systems will activate the vehicle’s braking in order to avoid a collision. These systems have been identified as being effective to avoid or reduce the severity of both head-on and run-off-road collisions (Austroads 2010h).

Crash modification Austroads (2010h) indicates that collision warning systems are expected to reduce fatal crashes (of any crash type) by 10–15% (CMF of 0.85–0.90) and serious injury crashes by 10–20% (CMF of 0.80–0.90). However, this excludes the additional crashes associated with a transfer of otherwise fatal crashes to serious injury crashes. A net reduction in serious injury crashes is still expected. Insurance Institute for Highway Safety (2014) indicates that forward collision warning systems can reduce multiple vehicle crashes by 5% (CMF of 0.95). Collision prevention systems reduce such crashes by 10–15% (CMF of 0.85–0.90). Insurance Institute for Highway Safety (2014) indicates that a combined lane departure and collision warning system reduces multiple vehicle crashes by 15% (CMF of 0.85). Injuries are reduced by 25% for occupants in the equipped vehicles, and by 40% to other parties.

ANCAP Vehicles are not necessarily tested or designed for maximum safety in all head-on collisions. The Vehicle Standard (Australian Design Rule 69/00 – Full Frontal Impact Occupant Protection) 2006 set the minimum requirements for how a vehicle in the Australian fleet should perform under frontal impacts. However, Fitzharris et al. (2006) have demonstrated that this minimum is insufficient to ensure occupants are free of risk of fatal or serious injuries. The Australasian New Car Assessment Program (ANCAP) conducts a suite of crash tests, including a headon offset crash test at 64 km/h. Vehicles are given a star rating (out of five) based on their performance in the crash tests, and the safety features present in the vehicle. To receive the maximum five-star rating, among other requirements, a vehicle is expected to provide good protection of vehicle occupants such that a headon offset crash at 64 km/h should be survivable for both driver and passenger. In contrast, the worst performing vehicles receive a one-star rating, and ANCAP (2015) indicates that occupants are likely to die from injuries sustained in this type of crash. One-star rated vehicles still meet the minimum requirements set by Vehicle Standard (Australian Design Rule 69/00), indicating the range of vehicles that may be accepted on Australian roads.

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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Austroads 2016 | page 73