Measuring the Impacts of Speed Reduction Technologies

Abstract

This paper presents the results of a quantitative and qualitative evaluation of a dynamic curve warning system deployed at one site on Interstate 5 in Oregon. On a dynamic message sign, the system displays messages directed to drivers on the basis of the observed speed of approaching vehicles. For the evaluation, three measures of effectiveness were selected: (a) the change in mean speed for passenger cars and commercial vehicles, (b) the change in the speed distribution for both passenger cars and trucks, and (c) public response to the sign. Speed samples were taken of vehicles with a laser ranging and detection device recording both speed and distance information over 7 days: four in the before period and three in the after period. The quantitative evaluation indicated that the advanced curve warning system was effective in reducing the mean speeds of passenger cars and trucks by approximately 3 mph for the southbound direction and 2 mph for the northbound direction. After the system was installed, the distribution of vehicle speeds was statistically different, with a lower number of vehicles in the higher speed bins. Because the system was installed only recently, crash reduction impacts have not yet been evaluated. Intercept surveys of motorists at nearby rest areas revealed a positive perception of the system. Overall, the results of the evaluation indicate that the advanced curve warning system is effective.