Glare susceptibility test results correlate with temporal safety margin when executing turns across approaching vehicles in simulated low-sun conditions

The purpose of this study was to compare the results of a laboratory glare susceptibility test with the execution of turns at an intersection (turns that required the driver to cross a lane containing approaching traffic). We measured glare susceptibility by means of low and high-contrast letter charts with and without a glare source. Driving performance in the absence and presence of simulated low sun was assessed using a simulator. In particular, we measured the difference between the time taken to complete a turn across the path of an approaching vehicle and the time to collision (TTC) with the approaching vehicle (the safety margin). The presence of glare resulted in a significant reduction in the safety margin used by drivers (by 0.65 s on average) and the mean number of collisions was significantly higher in the glare conditions than in the non-glare conditions. The effect of glare was larger for low-contrast than for high-contrast oncoming vehicles. Older drivers (45-60 years) had a significantly greater reduction in safety margin than younger drivers (19-29 years), though there was a large inter-individual variability in both age groups. We suggest that the reduction in retinal image contrast caused by low-sun caused drivers to overestimate the TTC with approaching vehicles.