Evaluation of Spatial and Temporal Speed Limit Compliance in Highway Work Zones

Typically, speed limits are reduced in work zones to safely accommodate construction activities and motorists on the roadway. This paper presents a methodology to evaluate the temporal and spatial effects of techniques designed to encourage compliance with work zone speed limits. The evaluations were performed over short and long segments within and adjacent to an Interstate construction work zone in suburban Indianapolis, Indiana, with the use of vehicle probe data. Space mean speed was measured by using 13 Bluetooth probe data acquisition stations, which provided a random sample of unique identifiers for approximately 11% of the passing vehicles. These space mean speed data were used to compute a series of comparisons between a day with no enforcement activity and a day with exceptionally high enforcement. During enforcement, the space mean speed decreased by approximately 5 mph throughout the 12.2-mi study segment. Within 30 min after the enforcement detail ended, however, space mean speeds increased, and there was no statistically significant residual impact on the space mean speed. Even at the absolute peak of enforcement, 75% of the probe vehicles exceeded the speed limit in all but one of the segments that had a posted speed limit of 45 mph. In addition, 25% of the probe vehicles exceeded the posted limit by more than 5 mph in all 45-mph segments during peak enforcement. The study is perhaps the largest ever conducted with respect to concurrent enforcement and extensive space mean measurement. The data represent an upper bound on the impact of enforcement activity on work zone speeds and should be of interest to public agencies as they consider compliance techniques.