Following the previous entry on signalised intersections, our focus now turns to unsignalised intersections (excluding roundabouts*), which may be either controlled or uncontrolled. Up to two thirds of all intersection crashes occur at unsignalised intersections according to US data. [1]
Controlled intersections
Controls at unsignalised intersections typically include Stop signs or Give Way (yield) signs on at least one of the intersection approaches. The conventional approach for unsignalised intersections is to give priority to the road of higher traffic volume and to maintain constant speeds on that road. However, a safe system approach is likely to include controls on all approaches, with appropriate speed management measures to reduce both crash risk and crash severity. Ideally, intersection design features should seek to ensure that potential impact speeds and angles are survivable for all road users. Pavement markings, median islands, advanced warning signs and raised platforms may all be used as supporting treatments.
At sites where vehicles are likely to conflict with pedestrians and/or cyclists, design features in a safe system approach should aim for speeds of no more than 30km/h. Where such speeds are unlikely to be achieved, segregation of the different road user types should be sought. Consideration should also be given to visual obstructions, line of sight, and the potential for inattentional blindness.
Uncontrolled intersections
Intersections lacking any specific controls are relatively rare and generally only found on low-speed roads of lowest traffic volumes, such as in rural, remote and some residential areas. Even where signs and other specific controls may be lacking, vehicles approaching intersections may be slowed with appropriate geometric design.
[1] Information sourced from Austroads Guide to Road Safety Part 2 and (US) FHWA “Intersection Safety”.
*Next week’s edition will take a look at roundabouts.