Final Technical Report TransNow Budget No. 61-6023 DEVELOPING AN AREA-WIDE SYSTEM FOR COORDINATED RAMP METER CONTROL

Ramp metering has been broadly accepted and deployed as an effective countermeasure against both recurrent and non-recurrent congestion on freeways. However, many current ramp metering algorithms tend to improve only freeway travels using local detectors' inputs and overlook the negative impacts on local streets. This may generate two problems: 1) the optimal local settings may not result in a system-wide optimum in terms of traffic operations; and 2) the increased congestion on local streets due to on-ramp overflow may counteract the gains in freeway operations. To address these problems, we propose an area-wide ramp metering system to improve the coordination of ramp meters for system-wide optimization and on-ramp overflow minimization. Our experimental results show that our method can offer improved performance in ramp metering operations under tested scenarios and also reduce the likelihood of on-ramp overflow. This novel strategy for active ramp metering is inspired by the principles of a computer network congestion control strategy. In this strategy, certain types of congestion at a targeted freeway location can be significantly reduced by limiting on-ramp vehicle flows to a fraction of ramp demand and then additively increasing rates to avoid ramp queue spillover onto city streets. This approach can be actively used to immediately curb the growth of traffic congestion and therefore shorten travel delays. The effectiveness of this ramp metering approach has been evaluated by microscopic simulation experiments. Our experimental results show that our method can reduce system-wide travel delays in the tested scenarios by as much as 28.2% when compared with the Fuzzy Logic ramp metering algorithm, and also reduce the frequency and severity of on-ramp overflow. This indicates that this area-wide algorithm can provide benefit when applied to urban freeway corridors for congestion mitigation.