Analysis of the Impact of the ATMS Deployment in Southeast Michigan
Investigator:	William C. Taylor, Department of Civil and Environmental Engineering

The objective of this project funded by the Michigan Department of Transportation, is to determine the impact of Variable Message Signs (VMS) on the level of congestion on the freeway network. This is accomplished by collecting and analyzing speed and volume data from over 2200 detectors located on the freeway network in Metropolitan Detroit. A typical speed profile is shown in Figure 1. These data are used to determine the numerical value of the Congestion Index (CI) at specific locations and across several corridors in the network. Data for the years 1997, 1999, 2000, and 2002 are compared to determine trends in congestion levels in both the morning peak period and the afternoon peak period. The data indicate that the CI values have decreased with the use of the variable message signs to communicate with the motorists.

Analysis of the detector data is also used to evaluate the impact of the VMS signs on driver behavior. The intent of a message displayed on these signs is to divert some drivers to alternate routes to reduce the severity and duration of incident based congestion. Comparison of the ratio of drivers that utilize alternative routes immediately downstream from the VMS when the sign displays a message warning of congestion ahead is used as a measure of the diversion effect of the signs. Figure 2 shows the freeway system near the location of one set of VMS installations, and Figure 3 shows the reduction in the percentage of vehicles delayed as a result of an accident when drivers are provided information on the accident location.