Assessing the Impact of Speed Limit Reduction near Signalized High Speed Intersections Equipped with Advance Warning Flashers: A Case Study in Nebraska

Adviser: Anuj Sharma This thesis evaluated the effects of 5 mph and 10 mph speed limit reductions in the vicinity of high-speed, signalized intersections equipped with Advance Warning Flashers (AWF). The selected methodology involved a field study of the impact of speed limit reduction at 7 high-speed, signalized intersections with AWF, using quantile regression models developed for speed. The quantile regression models for speed indicated that reduction of the speed limit from 60 mph to 55 mph did not have significant impact on observed speed during the green time. However, it was found that speed limit reduction from 65 mph to 55 mph led to statistically significant reductions in observed speed during the green period. The conclusions of this study, however, were limited by the low number of intersections where speed limits were reduced. Only two intersections with 10 mph reductions were available for observation where speed limit was reduced from 65 mph to 55 mph. Based on the available dataset, for a highway with a speed limit of 65 mph, a reduction to 55 mph at intersections equipped with AWF was found to be statistically significant in terms of reducing speeds over all speed percentiles during the green time. It is recommended that future research include other speed limit combinations, such as 5 mph reductions from 65 mph to 60 mph, and utilize larger datasets to provide for improved generalizability and transferability of results. A before-and-after study could also provide partially controlled conditions to isolate the impacts of speed limit reduction.