The purpose of this document is to outline the safety benefits that can result from road managers applying the principles of Western Australia’s Towards Zero road safety strategy.
Roads and roadsides and traffic safety
The quality of road infrastructure design plays a fundamental role in crash risk and in the severity of injuries in the event of a crash. This role is critical in two instances: in the initial design of the road and in the subsequent treatment of sites with high crash risk or incidence (blackspots).
The importance of improved road design can be demonstrated by black spot program evaluations which show that casualty crash frequency has been reduced on average by around 25-35% across all types of treatment, and by up to 90% for the best-performed countermeasures such as roundabouts and flexible roadside barriers (e.g., Scully, Newstead, Corben & Nimmi, 2006). Evaluations of best practice infrastructure improvements typically show Benefit-to-Cost Ratios (BCR) of around fiveto-one and even higher ratios for the best performing components of black spot programs.
These results show that substantial reductions in road trauma are readily achievable where design standards are improved, with the greatest gains being made where best practice is adopted. Best practice features introduced at the early design stage reduce both human and financial costs of road trauma that otherwise inevitably occur before accident black spot programs are able to detect and then address poor safety performance. Further, retro-fitting best practice designs can be costly and sometimes unaffordable, leaving road managers with little option but to reduce speed limits if improved safety is to be achieved. The trade-off between accessibility and safety then becomes a critical issue for debate and resolution.
To avoid burdening future generations with today’s (or worse, growing) levels of road trauma and the associated high costs of retro-fitting safety to Australia’s road network, it is essential that current design standards and practices are critically reviewed to meet Australia’s road safety vision to create a truly Safe System.
Safe road and roadsides – designing for Towards Zero in Western Australia Western Australia’s Towards Zero road safety strategy emphasises the need for roads to be forgiving of human errors. Road and roadside design practices must be transformed to ensure that these mistakes do not result in the loss of life or long-term health. To meet this challenge using a Safe System strategy, physical design features need to be considered in conjunction with kinetic energy or, in more common terms, vehicle speeds if a truly forgiving environment is to be produced.
Main Crash Types
Roads comprise two main elements: intersections and road lengths between intersections. Analyses of Western Australia’s serious casualty problem for the period 2005 to 2007 found that some 33% of serious casualties occurred at intersections, rising to 44% in metropolitan Perth (Corben, Logan, Johnston & Vulcan, 2008). A further 33% of serious casualties resulted from run-off-road crashes and in regional Western Australia, the run-off-road problem contributed almost 40% of all serious casualties.
Crash types at intersections that typically produce the most severe consequences include crosstraffic and side-impact crashes arising from turning right against on-coming traffic. At some locations, crashes involving pedestrians can be both prevalent and severe.
Along road lengths, the predominant crash types producing serious casualties are single-vehicle crashes into trees, poles, embankments and other roadside hazards, or involve over-turning. Headon collisions also produce serious casualties, making up 8% of regional serious casualties (Corben et al., 2008). In urban settings, pedestrian collisions are also common along road lengths and in metropolitan Perth account for approximately 10% of all serious casualties.
Biomechanical Limits of Humans to Crash
Violence These dominant crash types provide initial guidance for improving road and roadside design. Our knowledge of humans’ biomechanical tolerance of the forces, levels of acceleration and kinetic energy involved in key crash types also assists in designing a traffic system that minimises the loss of life and health.