Safety Evaluation of Sequential Warning Lights in Tapers at Nighttime Work Zones

Safety improvement at nighttime work zones is important because of visibility concerns after dark. The deployment of sequential lights is an innovative method to improve driver recognition of lane closures and work zone tapers. Sequential lights are wireless warning lights that flash in a sequence to delineate clearly the taper at work zones. The effectiveness of sequential lights was investigated with the use of controlled field studies. Traffic parameters were collected at the same field site with and without the deployment of sequential lights. Three surrogate performance measures (the speeds of approaching vehicles, the number of late taper merges, and the locations where vehicles merged into an open lane from a closed lane) were used to determine the impact of sequential lights on safety. The results of this study showed that sequential warning lights had a net positive effect: the warning lights reduced the speeds of approaching vehicles and enhanced driver compliance, and the lights shifted overall merge behavior upstream. Statistically significant decreases of 3.56 km/h (2.21 mph) mean speed and 1.61 km/h (1 mph) 85% speed resulted with sequential lights. The shift in the cumulative speed distributions to the left (i.e., speed decrease) was found to be statistically significant with the Kolmogorov–Smirnov test. With sequential lights, there was a statistically significant increase of 1.47 km/h (0.91 mph) in the speed standard deviation, and the percentage of vehicles that merged earlier increased from 53.49% to 65.36%.