Condition-responsive advisory speed 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 1.61 km (1 mi), 4.83 km (3 mi), and 12.87 km (8 mi) ahead of a work zone on a 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 with the speeds displayed in the messages. The results of the analysis indicate that the messages were somewhat effective in reducing speeds. Their effectiveness could have been improved if the distances between the PCMSs had been shorter and thus the message locations would have been closer to the points with lower traffic speeds. Driver interviews revealed that the advisory speed messages were understood and thought to be useful by most drivers who had seen them. However, some drivers questioned their usefulness and doubted their reliability, because they had not seen any reason to slow down.
Abstract