Advanced Research Project: Coordination of Freeway Ramp Meters and Arterial Traffic Signals Field Operational Test (FOT)

In current traffic operating practice, traffic control at freeway on-ramps and arterial intersections are operated independently. Such a situation may significantly reduce performance on both roadways. It is recognized that for highly efficient and reliable traffic flow over the entire traffic network, it may be necessary to coordinate the traffic between roads of different levels due to the strong dynamic interaction between them: one of the outputs of the arterial intersection is the immediate input of the adjacent freeway on-ramp. (This is also the case for freeway off-ramps and arterial intersections, but off-ramps are typically not under traffic control.) The efficiency of the overall traffic network relies on the performance of traffic control systems in different levels and optimal coordination as a whole.

Arterial intersection traffic control maximizes flow by progressively coordinating traffic signals over a series of intersections. Conversely, freeway on-ramp traffic control maximizes mainline flow by restricting traffic from entering the mainline if the total demand (upstream mainline flow + expected on-ramp flow) approaches or exceeds the capacity of the downstream mainline section. Another conflict is that arterial intersection traffic control groups vehicles into platoons, while freeway on-ramp metering tends to break these platoons into individual vehicles, usually one vehicle per green. If an onramp is subjected to serious storage limit, either through high arterial demand or low on-ramp discharge, traffic may spill back from the on-ramp into the arterial. Balance these two to achieve maximum flow or minimum Total Travel Time for the overall system is the critical issue.

Project Team:
Caltrans Division of Traffic Operations: TBD Zhongren Wang (email:, Tel: 1-916-654-6133)

Caltrans Division of Research and Innovation: TBD Fred Yazdan (email:, Tel: 1-949-936-3462)

Caltrans District 4: Alan Chow, Manager of Operation (email:, Tel: 1-510-286 4577) Lester Lee, Senior TE (email:, Tel: 510-286 4528) Sean Coughlin, Senior TE (email:, Tel: 510-286 4804)

Department of Transportation, City of San Jose: Lily Lim-Tsao, PE, Traffic Division Manager (email:, Tel: 1-408-975-3269)

California PATH: Alex Skabardonis, Traffic Program Manager, Principal Investigator Xiao-Yun Lu, Project Manager, Principal Researcher

California PATH will practically execute the project: fulfill the proposed tasks, produce deliverables, and writing report. Other stakeholders will actively participate in the project by providing advice, necessary facilities and monitoring the progress of the project.