Automated Speed Photo Enforcement Effects on Speeds in Work Zones

Abstract

Automated speed enforcement in construction zones has the potential to increase compliance with the speed limit and improve safety. The effectiveness of speed photo enforcement (SPE) (by radar) in reducing speeds and increasing speed limit compliance in work zones was evaluated for the first time in the United States, at Illinois work zones. Details are presented on SPE implementation and its effectiveness at the point it was stationed and at a downstream location in a work zone. Speed data were collected at the location of SPE and at a location 1.5 mi downstream in the work zone to determine the point and spatial effects of SPE. Speeds were measured for free-flowing and platooned cars and heavy vehicles in shoulder and median lanes. Results showed that SPE is effective in reducing the average speed and increasing compliance with work zone speed limit. The SPE reduced speed in the median lane more than in the shoulder lane, as expected. In addition, the speed of free-flowing vehicles was reduced more than for platooned vehicles. The reduction of the mean speed varied from 3.2 to 7.3 mph. The percentage of vehicles exceeding the speed limit near SPE was reduced from about 40% to 8% for free-flowing cars and from 17% to 4% for free-flowing heavy vehicles. Near the SPE van, none of the cars exceeded the speed limit by more than 10 mph, and none of the heavy vehicles exceeded it by more than 5 mph. The data also showed a mixed spatial effect for SPE. At the downstream location, the speed reduction for cars was not significant, while it varied from 0.9 to 2.5 mph for heavy vehicles.