Construction Area Late Merge (CALM) System

The system evaluated comprised 5 VMS, 4 RTMS, 2 microwave traffic sensors, and a laptop-based system control center, all integrated via UHF radio system. The system monitors traffic at each VMS and dynamically changes the messages displayed on the VMS and the operational mode of the system based on traffic conditions downstream of each respective VMS. Three operational modes were defined: early merge, late merge, and incident. Modes were characterized by traffic speeds. Threshold speeds where the system transitioned from one mode to another were based on prior research combined with site characteristics. The test site was an approach to a freeway to freeway interchange reconstruction in Kansas City. When the system was in late merge operation, lane distributions were statistically different than when in early merge operation, but the difference was small. An entrance ramp near the merge appeared to have a very strong effect on driver lane choice, influencing drivers to merge left, even when the system instructed them to hold their lanes. The system performed well (i.e., with few technical difficulties). The results underscored the importance of considering site characteristics very carefully when selecting sites for deployment of dynamic systems and/or late merge systems, and when designing the system deployment configuration.