A novel spatial analysis method to evaluate the safety impact of alternate road lighting

The aim of this paper is to introduce a new method to assess the safety impact of road treatment that influences long sections of road network, such as alternate road lighting, i.e. switching off every other road light at selected roads. The new method used Spatial Traffic Accident Analysis (STAA)–a network-based GIS hotspot analysis method–to identify and map day-time and night-time road traffic accident (RTA) risk levels before and after the implementation of alternate road lighting along a study road. Using the change after treatment in day-time RTA risk levels as a comparison group, and the change after treatment in night-time RTA risk levels as a treatment group, the difference between the treatment change and the comparison change in RTA risk levels was evaluated and mapped along the study road. The spatial distribution of this difference resulted in three different levels of the safety impact of the alternate light treatment at different locations along the study road: no impact, possible impact and highly possible impact. Night-time RTA after the alternate light treatment at road locations with the last two safety impact levels were identified, and their contributory factors were found most likely related to the reduction in night-time sight distance linked to alternate road lighting, and thus validates the safety impact results from the new method.