Evaluation of Work Zone Speed Limits: An Objective and Subjective Analysis of Work Zones in Missouri

This study objectively and subjectively examined speed characteristics and driver compliance with the posted speed limit in Missouri work zones. The objective evaluation collected vehicle speeds from four work zones with different configurations on I-44. The effects of lane closure, lane width reduction, and construction activity on speeds of cars and trucks were evaluated. Construction activity was found to have a statistically significant effect in reducing vehicle speeds. During no construction, passenger cars and trucks speeds were 3.5 and 2.2 mph higher than their speeds during periods of construction activity, respectively. The vehicle speeds were found to be statistically higher than the posted speed limit in all cases studied except when the lane width was reduced using tubular markers, which reduced the speed of cars and trucks by 8.5 and 11.1 mph for cars and trucks during construction activity, respectively. This figure was respectively 4.0 and 8.1 mph during no construction. Also, compliance with speed limits was lower for posted speed limits of 50 mph versus 60 mph. Two subjective evaluations were conducted: first, work zone speed limit practiced at state departments of transportations were surveyed, and second, drivers’ perceptions of driving through the work zones were investigated. Specific questions that evaluated driver perception were related to compliance with the posted speed limit, safety, and the effects of various factors on their speed. Results of subjective evaluation were consistent with the objective evaluation and showed that drivers suggest a work zone speed limit consistent with the speed that they drove through the work zone. When a work zone was mostly congested, 92% of car drivers and all of the truck drivers suggested a reduction in speed limits. Conversely, 92% of car drivers and 73% of truck drivers suggested a higher posted speed limit when the work zone was not congested. More than 90% of drivers agreed that construction activity prompted them to reduce their speed, a result that confirmed the outcome of the objective analysis.