Advanced Research Project: Field Test of Combined Variable Speed Limit and Coordinated Ramp Metering for Freeway Traffic Control

The goal of cooperative vehicle-highway systems is to increase system performance and sustainability (e.g., road safety, mobility, emissions impacts, fuel savings, customer satisfaction, etc.) by planning and using communications and sensor infrastructure seamlessly in order to improve the overall performance of the driver/traveler-vehicle-roadway system. Speed harmonization is one of the strategies within cooperative vehicle-highway systems, but as presently implemented with the use of variable speed limit signs, it has limited effectiveness because it depends upon unpredictable and uncoordinated behavior of drivers in response to these signs. Further, speed harmonization systems that are currently deployed are costly to install as they may require gantries and signs to provide the advice. Recent research sponsored by FHWA has found that new traffic flow optimization methods can significantly improve traffic flow and performance through speed harmonization [1].

This project implemented speed harmonization by developing and testing traffic flow optimization models and algorithms to establish target speeds by highway section and then continuously (or nearly continuously) communicating speed guidance directly into the vehicles with minimal distraction of the driver, but with the driver maintaining supervisory control at all times. This project was executed in the STOL at TFHRC and associated LLs. LLs include open road facilities where testing with live traffic can be done within acceptable safety limits and with permission of roadway owners. Such an LL were equipped with data collection capabilities to support research, and not just be used for demonstration. Instrumentation was deployed and tested at the STOL and then deployed in multiple operational roadway locations in keeping with the LL paradigm. This work will prepare and test roadside infrastructure as well as variously automated vehicles in the STOL local setting, and then deploy the actual STOL LL research effort to selected freeways and/or arterials.


  • [1] Freeway Traffic Control Using Variable Speed Limits, X. Lu, C. Nowakowski, D. Su, S.E. Shladover, PATH, June 2011, Report under Cooperative Agreement DTHFH61-07-H-00038.