Description: The D-25 Speed Advisory Sign System was intended to warn drivers of stopped or slow-moving traffic ahead and thereby enable them to reduce their speeds and avoid rear-end crashes with these vehicles. The three speed trailers were operated independently, and the speed displays showed the speed of the downstream traffic. When a traffic slowdown was detected, the strobe lights began flashing. When there was no slowdown, the strobe lights were off, and either the speed of traffic downstream or the work zone speed limit was displayed, which ever was lower. The system deployed for the purpose of the field evaluation consisted of three speed trailers placed at approximately ¼-mile interval in advance of a work zone on Interstate 80 near Lincoln, Nebraska. The results of the analysis indicated that the speed messages were effective in reducing the speed of vehicles approaching queued traffic during time periods when congestion was building. The speed profiles observed during the operation of the speed advisory system were generally smoother than those observed before system deployment. Before the trailers were deployed, vehicles began decelerating later but more intensively than after their deployment. Deceleration pattern at the trailer farthest from the lane closure taper (trailer 3) has completely changed when the speed trailer began displaying speed messages. Before system deployment most drivers only slightly reduced their speed between the first two speed measurement points, and they mostly reduced their speed between the second and third measurement points. After system deployment, motorists at trailer 3 decelerated more before they reached the speed trailer than after they passed it. Due to the limited time available for the field studies the long-term effectiveness of the speed advisory system could not be determined.
Report: MwSWZDI-2002-Pesti-D-25_Speed_Advisory_System.pdf 458 kb (published 2002)
State conducting research: Nebraska