Speed Reduction Effects of Speed Monitoring Displays with Radar in Work Zones on Interstate Highways

The speed monitoring display is a traffic control device that uses radar to measure the speeds of approaching vehicles and shows these speeds to traffic on a digital display panel. It is intended to slow traffic by making drivers aware of how fast they are traveling. In addition, it is expected that its radar will also cause some drivers using radar detectors to slow down. The effectiveness of this device was evaluated at a work zone on an interstate highway in South Dakota. The speed monitoring display reduced mean speeds and excessive speeds on the approach to the work zone. Mean speeds were reduced by 6 to 8 km/hr (4 to 5 mph), and the percentages of vehicles exceeding the advisory speed limit of 72 km/hr (45 mph) were reduced by 20 to 40 percentage points. These speed reductions are greater than those reported for the use of radar alone.