Safety in highway work zones has become a concern among Departments of Transportation (DOTs) throughout the country as the highway network has begun to age and more maintenance and construction work has been necessary. Safety in highway work zones is more compromised than in other areas for two reasons. First, the construction workers are near traveling vehicles as they perform their already dangerous work, increasing the risk of an accident. Second, the highway user is at increased risk because of the increase in roadside obstacles, because other vehicles are more likely to act in unpredictable ways (such as sudden braking or lane changes), and because vehicles are more likely to be traveling closer together (due to decreased capacity). Researchers are looking at several mechanisms for improving safety in highway work zones, including lowering the mean speed of vehicles in the work zone, encouraging drivers to be alert in work zones, improving the control of traffic in merging areas, and improving the safety devices that separate vehicles and construction workers. This study focuses on the goal of reducing speed in work zones. First, methods of speed reduction used by state DOTs throughout the country are identified, and the research surrounding them is summarized. Next, the methodology and results of a field study that tests the efficacy of the Speed Monitoring Display (SMD) are described in detail. Finally, the results of a survey that was conducted to ascertain drivers' opinions of the SMD are presented. For the field study, three main conditions were analyzed: a no-treatment case, with the MUTCD signs and barriers; a treatment case using the SMD; and a treatment case using a police vehicle. In the no-treatment case, average vehicle speed was reduced about 3 mph as vehicles entered the work area of the work zone. With the SMD, average vehicle speed was reduced an additional 4 mph. With the police vehicle, average vehicle speed was reduced about 6 mph more than in the no-treatment case. Thus, average vehicle speed was reduced in all treatment cases; however, the police vehicle was slightly more effective than the SMD at reducing average speeds. (These conclusions are valid at a 95 percent confidence level.) The results of the survey also suggest that the SMD is a promising option for state DOTs. According to drivers' self-reports, those who normally drive a little faster than the speed limit are likely to slow down in reaction to an SMD, but drivers who normally ignore the speed limit are likely to ignore an SMD. The majority of drivers surveyed had positive reactions to SMDs, reporting that they feel SMDs are accurate, not distracting, and not difficult to read.



College and Department

Ira A. Fulton College of Engineering and Technology; Civil and Environmental Engineering



Date Submitted


Document Type





speed display, speed monitoring display, speed limit, work zone, police, police enforcement, construction, maintenance