Assessing the impact of low-speed limit zones' policy implications on cyclist safety: Evidence from the UK

As part of the shift in policy to promote active travel, the UK's Manual for Streets (MfS) guidance proposed new approaches for priority intersections design in residential areas, promoting lower geometric visibilities for drivers on minor road arms to reduce collision severity, and the low-speed (i.e., 20 mph) limit zone policy. However, the relationship between speed, visibility, and collisions has not been explored comprehensively for these low-speed limit residential areas. This study aimed to evaluate the impact of shorter visibilities on vehicle-bicycle collisions at priority intersections in Portsmouth, UK. Using piecewise Structural Equations Modeling and Artificial Neural Network models, 120 locations in the city were analysed to understand the complex interplay between vehicles' speed, speed limits, visibilities, geometries, traffic flows, and collisions. The research question was whether shorter visibilities supported policy intentions by reducing bicycle collisions in low-speed limit areas, as MfS suggested. The results show that greater visibility 9 m back to left and right positively correlates with higher road traffic collisions. In comparison, greater left-hand visibility at 2.4 m back from minor arms has a counter-effect that improves safety. This supports the notion that shorter visibility in residential areas aid cyclist safety. This study contributes significantly to the literature by shedding light on the impact of shorter visibility on road safety. The findings have important implications for transportation policy and practice, highlighting the importance of the MfS approach for improving cyclist safety in the design of priority intersections.