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.

A Comprehensive Review of Dynamic Speed Feedback Signs in Reducing Speed at Different Critical Locations

“…Researchers also evaluated the effects of DSFS on drivers of different vehicles, primarily cars and trucks. Several studies found no significant differences in speed reduction between cars and trucks [4,11,18]. Some studies found that the effect of speed reduction was greater for passenger cars than for other vehicles (heavy vehicles) [1,6,9], while several recent studies found that DSFS had greater effects on drivers of heavy vehicles [7,26,42].…”

“…In 2006, Monsere et al examined two overhead DSFSs on a horizontal curve on the interstate in a before-and-after study [18]. The overhead sign indicated the highest speed within the detection zone.…”

“…However, a variety of messages have been used and are listed in Table 7. "YOU ARE SPEEDING" followed by "SLOW DOWN", "YOUR SPEED IS______" followed by "SLOW DOWN", "YOUR SPEED IS______" followed by "THANKS FOR NOT SPEEDING" or "SLOW DOWN", and "YOU ARE SPEEDING" followed by "MINIMUM FINE $200" Overall, full-matrix displays that can switch between showing the current driving speed and providing supplementary warnings like "SLOW DOWN" when the driver surpasses the speed threshold have been observed to be more effective than signs that solely display the driver's speed [17,18,19,34]. Finally, triggering has also been mentioned as a possible factor, although more solid evidence is lacking.…”

“…In most studies, triggering speed was set relative to the speed limit. As described in the previous paragraph, some studies have displayed different messages depending on speed [10,18] however, some researchers have also suggested that uniform triggering may not be appropriate for the dynamic nature of traffic as well as for warning different types of vehicles. Jomaa et al investigated the effects of triggering speed on driving speed and its standard deviation [43].…”