Improving safety at nighttime work zones is important because of the extra visibility concerns. The deployment of sequential lights is an innovative method for improving driver recognition of lane closures and work zone tapers. Sequential lights are wireless warning lights that flash in a sequence to clearly delineate the taper at work zones. The effectiveness of sequential lights was investigated using controlled field studies. Traffic parameters were collected at the same field site with and without the deployment of sequential lights. Three surrogate performance measures were used to determine the impact of sequential lights on safety. These measures were vehicle speed and speed variability, vehicle lateral position at taper, and vehicle merge location. The results of this study indicate that sequential warning lights had a net positive effect in reducing the speeds of approaching vehicles, enhancing driver compliance, and shifting the overall merge behavior upstream. Statistically significant decreases of 2.21 mph mean speed and 1 mph 85% speed resulted with sequential lights. The shift in the cumulative speed distributions to the left (i.e. speed decrease) was also found to be statistically significant using the Kolmogorov-Smirnov test. But a statistically significant increase of 0.91 mph in the speed standard deviation also resulted with sequential lights. With sequential lights the percentage of vehicles that merged earlier increased from 53.49% to 65.36%.