Balancing infrastructure improvements and speed limits

Both infrastructure and speed limits play a significant role in the safety performance of the road network, and they are linked. Although many road crashes are attributed to human error, the severity outcome from any given crash is most strongly dictated by the infrastructure and environment that is provided. If protective infrastructure is present (for example a flexible roadside barrier instead of a tree) or the design of the road encourages speeds within human tolerance levels to injury, then the injury outcome is more likely to be of low severity.

There is very clear evidence about the safety benefits of both improved infrastructure and provision of appropriate speed limits. Evaluations have shown that provision of certain infrastructure (e.g. roundabouts, and flexible barriers in the centre and on the edge of high speed roads) virtually eliminates fatalities and serious injuries. However, extensive rollout of higher cost infrastructure tends to be limited to high volume roads. In the short to medium term, lower speeds limits can produce significant safety benefits. With speed reduction benefits there is a ‘power’ effect, meaning for even small reductions in speeds, there is a substantial reduction in risk, particularly for fatal and serious crash outcomes. As an example, a 10 km/h reduction in speed on a high speed road would result in over a 30% reduction in fatal and serious injury. Speed reduction is influenced by changes in speed limits, but this often needs to be supported by appropriate infrastructure. Austroads has provided recent guidance on this issue for high speed roads as well as urban arterial networks.

There are many examples around Australia demonstrating the safety benefits of improved infrastructure. These include lower cost infrastructure measures used on lower volume roads such as the rollout of sealed shoulders and audio-tactile line marking in Western Australia. Lower cost infrastructure measures are often supported by more appropriate speed limits, such as Queensland's Bruce Highway where wide centreline treatments were used in combination with lower speed limits. For higher volume roads there has also been extensive rollout of wire rope barrier systems, including in South Australia, New South Wales, Victoria and Tasmania.

This Action Plan builds on the success of previous infrastructure and speed-related safety improvements with a number of new initiatives. Actions 12 and 3, with Actions A and B, are together aimed at achieving 3-star AusRAP ratings or better on the most-travelled roads and improving safety on low-standard regional and remote roads. This will be done through a combination of implementing proven safety treatments, reducing speed limits on low-standard roads, and targeting safety-focused infrastructure funding. Action A calls for the establishment of network-wide safety plans for corridors, involving further application of treatments known to reduce fatalities and serious injuries, as well as improving design and the approaches to address risk for specific groups through infrastructure improvements. Action 3 calls for a combination of infrastructure and speed reduction measures to reduce trauma at urban intersections.

There are also specific actions relating to application of safer speeds. Action 6 highlights the need for lower speed limits to address vulnerable road user safety, and Action 7 calls for increased use of point-to-point and mobile speed cameras, while Action D involves the development of a national speed enforcement strategy.