Effect of Condition-Responsive, Reduced-Speed-Ahead Messages on Speeds in Advance of Work Zones on Rural Interstate Highways

Condition-responsive, reduced-speed-ahead messages were evaluated as part of the Midwest States Smart Work Zone Deployment Initiative, a pooled-fund study sponsored by Iowa, Kansas, Missouri, Nebraska, and the Federal Highway Administration. The messages were displayed on three portable changeable message signs (PCMSs) placed approximately 1, 3, and 8 miles in advance of a work zone on rural interstate highway in Nebraska. The messages were intended to advise drivers of the speed of slower traffic ahead and thereby encourage them to slow down. Speeds downstream of the PCMSs were measured and compared to the speeds displayed in the messages. The results of the analysis indicated that the messages were somewhat effective in reducing speeds. It was concluded that their effectiveness could have been improved if the distances between the PCMSs had been shorter so that the locations where the messages were displayed would have been closer to the points where traffic speeds were actually lower. Driver interviews revealed that the reduced-speed-ahead messages were understood and thought to be useful by most drivers who recalled seeing them. However, some drivers questioned their usefulness and doubted their reliability, because they hadn’t seen any reason to slow down.