Applying the Twilight Envelope to the Forensic Analysis of Pedestrian and Bicyclist Conspicuity in the Dark

Abstract

The large majority of traffic crashes involving vulnerable road users such as pedestrians and bicyclists occur when ambient illumination levels are reduced. The difficulty drivers face in recognizing the presence of these road users in the darkness can be attributed to the selective degradation of foveal visual functions, which support a driver’s ability to detect and identify the presence of potential hazards and other objects in the environment. Clothing worn by pedestrians and bicyclists can contribute to their conspicuity to oncoming drivers; extensive research has demonstrated that dark-clothing-clad pedestrians are often recognized at dangerously short distances. Vehicle headlamps serve to illuminate the path ahead for drivers, particularly in the absence of artificial illumination along the roadway, in order to improve driver visibility in the dark. The twilight envelope is a means of determining the visibility distance afforded by headlamps. This approach to describing illumination was applied to the analysis of a traffic crash involving a vulnerable road user, providing insight into the driver’s visibility. Future research should address the relationship between the twilight envelope of vehicle headlamps and the distance at which drivers are able to recognize potential hazards such as pedestrians and bicyclists using those headlamps.