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Mid-America Transportation Center

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

Final Report
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Missouri University of Science & Technology


  • Principal Investigator: Ghulam Bham ( (573)341-6286)
  • Graduate Students
  • Krishna Vallati Manoj
  • Mojtaba Mohammadi
  • Undergraduate Students
  • William Frederickson
  • Project Status
  • Start Date: 3/10/2008
  • End Date: 8/31/2010
  • Sponsors & Partners
  • Smart Work Zone Deployment Initiative
  • Mid-America Transportation Center
  • About this Project
    Brief Project Description & Background
    Many states have enacted temporary speed reduction regulations for work zones, and a variety of speed limits are in place. Experience has shown that the effectiveness of signs in reducing the speed of traffic through work zones varies. The differences in speed limit have made enforcement difficult as motorists often do not follow or fail to notice changes in speed limits. Moreover, hazardous conditions for drivers and construction workers are common in work zones because construction activities disturb normal traffic flow. Ensuring safety in work zones while maintaining highway capacity has become one of the most overwhelming challenges confronted by traffic engineers and researchers.
    Research Objective
    In cooperation with the Missouri Department of Transportation, the research team objectively investigated traffic speeds and driver compliance with posted speed limits in work zones on I-44 to systematically assess the impact of static speed limit signs.
    Potential Benefits
    Most state DOTs continue to rely on static speed limit signs to reduce speed in work zone, even though static signs are largely ineffective at ensuring driver compliance with the posted speed limit. Static speed limits remain the same regardless of construction activity. This can lead some drivers to ignore speed limit signs, which results in higher variance in the vehicle speeds. Variable speed limit signs can be adjusted in real time based on the traffic congestion and construction activity. This will help in the mobility and safety of traffic during periods with no-construction activity.
    This study objectively and subjectively examined characteristics of vehicle speeds and drivers’ compliance with the posted speed limit in work zones. The objective evaluation extracted free flow speeds of vehicle from four work zones with different configurations located on I-44. The free flowing speeds of cars and trucks were evaluated using statistical tests, and studied the effects of lane closure, lane width reduction, and construction activity on vehicle speeds. Vehicle speeds were statistically higher than the speed limit in all cases studied except when the lane width was reduced using tubular markers. The subjective evaluation conducted two surveys. State departments of transportation (DOTs) were surveyed about common practices in work zones and drivers’ perceptions of traveling through a work zone were assessed. The dominant factors that DOTs use to determine reduced speed limits are the presence of workers, lane width, roadway alignment, and type of activity. Most DOTs rely primarily on static speed limit signs, but only 25% of the respondents found such signs effective. Questions on the driver survey addressed safety, speed in work zones, compliance with the posted speed limit, and the effects of various factors on speed. The results were consistent with the objective evaluation and most drivers suggested a work zone speed limit consistent with their own speed.
    Total Project Cost
    $ 15,000
    Modal Orientation
  • Highways
  • Multimodal Transportation
  • Safety and Human Performance
  • Work Zones