The California Variable Speed Advisory Project

Variable Speed Advisory (VSA) is an Active Traffic Management strategy, with the goal of affecting driver behavior on freeway mainlines.

The function of the VSA algorithm is to maximize the bottleneck capacity flow, and to gradually and properly decrease the speeds from the most upstream sign to the bottleneck location in order to achieve the highest throughput, reduce the shockwave, and hopefully eliminate the queue.

This pilot VSA project is to test the effectiveness of the VSA concept using the algorithm developed by PATH research on eastbound SR-78 as indicated in the map above. The roadside VSA signs will display the advisory speeds at increments/decrements of 5-10 mph on based on the traffic conditions during the AM/PM peak periods. The information to be updated at this website every 30 s will include: aggregated occupancy, flow and speed from Caltrans District traffic detector stations, radar speed from VSA signs, and message and advisory speed displayed on the VSA signs.

The Caltrans/UC Berkeley PATH Variable Speed Advisory Project is a joint project sponsored by the Caltrans Division of Research, Innovation and System Information (DRISI), and Caltrans District 11 (San Diego). It is developed and managed by the University of California at Berkeley Institute for Transportation Studies (ITS), Partners for Advanced Transportation Technology (PATH)