Sealed shoulders
Sealing of road shoulders provides road safety benefits and reduces costs associated with pavement maintenance. Sealed shoulders reduce run-off-road (ROR) crash rates by providing opportunity for drivers to recover from inadvertent lane departure, while also providing a buffer between roadside objects and the traffic lane. Further benefits include the provision of space for vehicles to stop clear of the traffic lane when necessary, and space for vulnerable road users such as cyclists to separate from larger motorised vehicles.
Effectiveness
Sealed shoulders of adequate width are associated with significant crash rate reductions, with such width ranging from 0.5 - 2.0m depending on road environment factors such as speed, geometry, road user types, and others. In Australia, rural roads with minimal or no sealed shoulder have been found to have almost twice the risk of casualty crashes than roads with sealed 2m shoulders (Austroads 2024 Guide to Road Safety Part 2). Safety benefits are especially evident on the outside of horizontal curves, but also clearly apply to other sections. These benefits are likely to be enhanced when combined with complementary treatments such as audio-tactile line marking (ATLM) and/or wide edge lines.
Considerations
Sealed shoulders can be considered a supporting treatment to help reduce both crash risk and crash severity. The presence or absence of barriers, clear zones, drains and other roadside features and treatments should be considered when planning for shoulder enhancement or modification.
Durability of pavement including on shoulders can be enhanced through sloped pavement edges to eliminate vertical drop-offs, which are more prone to erosion and more likely to contribute to loss of control crashes of errant vehicles.
Insufficient available space may often preclude shoulders of appropriate or desirable width. Steep cuttings, embankments and culverts are among a wide range of environmental constraints. Other treatments such as wide centrelines and median barriers may substantially reduce the available shoulder width. In such cases, rigorous cost-benefit analyses should be used to determine prioritisation of treatments which compete for lateral space.
