Does the reduced visibility at priority-controlled intersections influence cyclist safety? Findings from a case study in the UK

In 2007, the UK’s Manual for Streets (MfS) was published, which set out new approaches to designing priority intersections in built-up areas. This promoted lower visibilities for drivers on minor road arms compared to those in the UK’s Design Manual for Roads and Bridges (DMRB). By reducing the visibilities for drivers, MfS aimed to reduce the corresponding speeds of drivers on the minor road approach, thus reducing the level and severity of collisions. Portsmouth became the first city in the UK to adopt 20mph speed limits in most built-up areas in 2007. Existing studies on vehicle-bicycle collisions at priority intersections indicate vehicles' speed and visibilities as key determinants. However, these relationships in the context of low-speed limit areas have not been explored in the literature. This research evaluates the effect of visibilities at low-speed (20mph) intersections through analysis of 120 locations around the city of Portsmouth. Structural Equations Modelling and Artificial Neural Network models were built and compared to represent the complex interplay between vehicles' speed, speed limits, visibilities, geometries, traffic flows, and collisions. This research sheds light on the effects of reduced visibilities on motorised vehicle collisions with bicycles in the context of low-speed and low-speed limit priority intersections.