Knowledge Resources

The Illinois DOT used ITS during reconstruction of a 40-mile section of Interstate 55 including the Lake Springfield Bridge. Reconstruction of the bridge involved closing the southbound span and diverting southbound traffic onto the northbound span, and then reversing the process once work on the southbound span was complete. To minimize congestion and improve safety in the work zone, the DOT deployed a Real Time Traffic Control System (RTTCS) from February 2001 to May 2002. The RTTCS consisted of 17 portable dynamic message signs (DMSs), 8 portable vehicle detectors, and 4 portable closed circuit television (CCTV) cameras linked to a central computer via a wireless communication system. The field components were solar powered.

The DMSs displayed a variety of messages including delay information, lane closure advisories, and the number of citations for moving violations. The CCTV camera images were used to confirm traffic and incident data. The central computer monitored traffic flow data from the vehicle detectors, calculated delay at each detector location, automatically displayed preprogrammed messages on DMSs, updated a real-time traffic condition map on the project website, and provided congestion and incident alerts for Illinois DOT staff via email or pager.

Although no official evaluation of the RTTCS was performed, DOT officials were satisfied with the performance of the system. There were only two crashes in the work zone due the lack of traffic backups and ample motorist warnings provided via DMSs. Safety was also enhanced by advisory messages on the number of citations that had been issued in the work zone. DOT staff reported a significant decrease in the number of moving violations after the system began displaying these messages.