Coordination of Freeway Ramp Meters and Arterial Traffic Signals Phase II-B - Field Implementation

The independent operations of freeway ramp meters and the adjacent arterial intersection traffic signals often causes queue spill back on the freeway on-ramps and the surface street network that result in activation of queue override, which negates the benefits of ramp metering. This is due to the lack of coordination between the two traffic control systems which are usually operated by different agencies. Field measurements at a real-world test site show that queue override reduces the freeway bottleneck capacity by 10%. A control strategy for coordinating freeway ramp metering and arterial traffic signals was developed, field implemented, and evaluated in this study. The algorithm takes available on-ramp storage into account and dynamically reduces the cycle length of the feeding intersection signal control in order to avoid on-ramp queue spill-back and mitigate unnecessary delay in the conflicting directions. The proposed algorithm was tested in the morning peak during a four-month period. Observations in the field suggest that the proposed control was able to significantly reduce travel time and delay on freeways while preventing on-ramp queue spill-back to arterials.