California Partners for Advanced Transportation Technology

Freeway ramp metering is an effective control strategy to preserve freeway capacity, reduce freeway delays, and improve travel time reliability. The ramp metering operation may cause on ramp queue spillback that interferes with the adjacent surface streets. In such situations, most ramp metering systems employ a “queue override” function, which temporarily suspends ramp metering to dissipate the on-ramp queues. A detailed field study was performed at a metered freeway on-ramp merge in San Jose, California using video recordings. The analysis of the collected field data over a two week period show that the freeway bottleneck discharge flow is reduced by 10% on the average when the queue override is activated. The paper provides suggestions for managing queue spillbacks at metered on-ramps.