Truck-mounted radar speed signs were effective in reducing traffic speeds by 5 to 23 percent versus reductions of 4 to 8 percent in work zones without them.

Evaluation of the use of radar speed displays for mobile maintenance operations at four sites in Oregon.

Date Posted

Evaluation of Radar Speed Display for Mobile Maintenance Operations

Summary Information

Workers performing mobile highway construction and maintenance operations have traffic moving only a few feet from their work area. Maintenance zone fatalities represent about 10% of all work zone fatalities. Maintenance operations typically consist of mobile operations over a short period. Examples include sweeping, surface patching, and line painting. This study evaluates benefits and limitations of using a truck-mounted radar speed sign (RSS) during mobile maintenance operations by examining four case studies.


The RSS was installed on an Oregon Department of Transportation (ODOT) maintenance truck, a vehicle moving along at a low speed (5-10 mi/h) behind maintenance equipment to warn drivers to slow down. The RSS was a full matrix model with 3 lines of 10-inch characters with the capability of showing different messages. Vehicle characteristics (vehicle type, speed, length, time of day, etc.), gathered with 14 traffic sensors, were the primary data collected. For each of the four operations selected (relamping, sweeping, spraying, and vactoring drains), two periods of testing were compared: one with the RSS turned on (treatment) and one with the RSS turned off (control).


Overall, the RSS display was effective in reducing vehicle speeds in the work zone. Quantitative analyses of speed data from the case studies find:

  • Decrease in vehicle speed between Road Work Ahead (RWA) signs and an active work area is greater with the RSS display turned on, 85th percentile speeds decreased by 2-5 mi/h (4%-8%) with the RSS turned off and 3-13 mi/h (5%-23%) with the RSS turned on.
  • Vehicle speed decreases while approaching and passing work equipment in all situations, but the 85th percentile speeds were about 2 mi/h less with the RSS display turned on.
  • There is a reduction in the percentage of drivers exceeding the speed limit between the RWA sign and work zone. The decrease is greater with the RSS turned on (27% to 48%) than when turned off (15% to 35%).
  • Mean speeds of those exceeding the speed limit with the RSS turned on ranged from 59.9 mi/h to 61.6 mi/h and from 59.5 mi/h to 62.8 mi/h without the RSS turned on.

An easy to use, mobile, and multi-functional traffic control device was found to help lower vehicle speeds and lower differential speeds between adjacent vehicles in maintenance work zones.

Goal Areas
Results Type
Deployment Locations