A sign of the times

Dynamic message signs (DMS) are used on roads to keep drivers informed of conditions ahead. This study looks at the effects these signs have on driver behavior. The study involved online surveys through the Minnesota and Washington State Department of Transportation websites to obtain feedback from travelers on the use of travel time information. The Washington survey concentrated on the Seattle area. A high number of people said they have exited the highway and taken an alternate route due to DMS displays with longer than expected travel time estimates. There was a broad variance in delays shown before travelers diverted. Minnesota drivers diverted when the DMS displayed 5-10 minutes worth of delays, and Seattle drivers changed routes when the DMS reported a 15-20 minute delay. The study also evaluated traffic volume data, and findings confirmed the results of the survey. In Minnesota, DMS displays showing a travel time of five or more minutes than expected resulted in an increase of traffic diverting from the freeway. For delays of more than ten minutes, an even higher volume exited the freeway. Seattle had fewer instances of travel time delays being reported on the DMS, but the pattern showed that some drivers diverted when ten minutes of delays were reported, and even more did when delays were 20 minutes or more. An explanation for the difference in findings between Minnesota and Seattle is the distance DMS displays are spaced on the road. In Minnesota, they are usually 5-8 minutes apart in normal traffic, while those in the Seattle area are about 15-20 minutes apart. The findings suggest that when the travel time posted is double what is expected, drivers will divert. The findings of the study can help in understanding drivers' reactions to travel information, which can help in traffic management.


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  • Accession Number: 01495016
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Sep 17 2013 8:34PM