Use of Radar-Equipped Portable Changeable Message Sign to Reduce Vehicle Speed in South Carolina Work Zones

This research examines the use of radar equipped portable changeable message signs to reduce driver speeds in South Carolina DOT work zones. The 85th percentile speed, mean speed, and percentage of vehicles exceeding the speed limit were considered in evaluating four different message sequences tested within a two-phased data collection effort, and generally exhibited a range in speed reduction from 3 to 10 mph (4.8 to 16.1 km/h). All message sequences were found to reduce driver speeds, and two were selected for further study based on their effects and novelty. Research data support the findings that radar equipped changeable message signs are an effective means to reduce vehicle speeds in localized areas. Data collection and analysis are focused on singling out individual speeding vehicles and providing the driver specific messages. The messages evaluated in this research included special instructions, speed notifications and feedback, and the magnitude of legal penalties. However, long-term impact of messages on motorists was not evaluated; rather attempts were focused on finding the most effective speed reduction message sequence. Previous research on the use of changeable message signs with radar as a work zone speed reduction device is discussed.