Enhanced delineation at horizontal curves can alert drivers to the sharpness of upcoming curves and encourage appropriate speeds for safe navigation. This can be achieved through a range of treatments, including chevron signs, retroreflective post markers, wide pavement markings and edge lines, dynamic and sequential curve warning signs, and speed feedback signs, among others.
Traffic calming measures can help to reduce run-off-road (ROR) crashes by reducing and moderating vehicle speeds using physical and perceptual treatments. These include speed platforms, traffic islands, narrow lanes and line marking, changes in delineation, surface colour and/or texture. Such measures are primarily used in low-speed urban environments.
Effectiveness
The effectiveness of chevron signs and in-lane curve warnings has been demonstrated in US research. Standard and oversized chevron signs produced up to 16% reductions in fatal and injury crashes, and 25% reductions in night-time crashes. Greater crash reductions are reported for sequential dynamic chevrons (60%) and in-lane curve warning pavement markings (up to 38%) (US Federal Highway Administration).
Traffic calming measures are most often used in urban environments to reduce vehicle speeds, with a focus on protecting vulnerable road users. Lowering speeds reduces the risk of ROR crashes which may involve pedestrians, as well as reducing the risk of other crash types. While the safety benefits of individual and combined treatments depend on many site-specific factors, Australian research has found traffic calming measures to reduce serious and fatal pedestrian crashes by as much as 70% (Austroads 2024 Guide to Road Safety Part 2).
Considerations
From a safe system perspective, guidance and traffic calming can generally be considered as supporting treatments and are applicable in a range of different environmental contexts. While there is considerable overlap, guidance treatments such as curve warnings and retroreflective post markers are common for high speed roads, where traffic calming measures may often be appropriate for low speed environments only.
