Evaluation of Ramp Control Effectiveness in Two Twin Cities Freeways

Abstract

Recent public opposition threatened to eliminate ramp control as a traffic management option in the Twin Cities of Minneapolis and St. Paul, which have one of the most extensive ramp control systems in the nation. In response to this, the Minnesota Department of Transportation had to produce tangible independent evidence that ramp metering is effective, to avoid turning off the meters. Simulation is the most widely accepted technique for achieving the stated objectives without turning the metering system off, and therefore it was used in this study. Two freeway sections were selected for detailed testing, and the results along with the methodology are presented here. The results confirm that ramp metering is effective on the ramp and freeway system (not just the freeway), but they also revealed excessive delays on certain ramps that appear to support the concerns raised by the users. Real-life issues related to the simulation implementation process (data collection and filtering, calibration, and interpreting and summarizing results) are also presented. Through the course of this work, simulation reliability was established by defining a successful calibration and validation methodology and by identifying, in the process, certain operational problems related to the deployed surveillance and control system that had been unknown. Finally, a general methodology was developed for evaluation that can easily be adapted to any user-specified control strategy or used to improve an already existing one without field disruptions.