Coordination of Freeway Ramp Meters and Arterial Traffic Signals Phase IIA – Site Selection and Simulation Development

The independent operation of freeway ramp meters and the adjacent arterial 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. The objectives of this study are to develop and implement a control algorithm for coordinated operation of metered freeway on-ramps and adjacent signalized intersections. The report describes the research performed in phase IIA of the project: development of a control algorithm, test site selection, and evaluation of a proposed algorithm on the test site through simulation. The field implementation and testing of the proposed algorithm at the selected test site will take place in the upcoming phase IIB of the project. A control algorithm was developed and evaluated at a real-world test site. The algorithm considers the available on-ramp storage and dynamically reduces the cycle length in order to avoid on-ramp queue spill-back and mitigate unnecessary delay in the conflicting directions. The simulation results show the proposed coordination strategy eliminated the queue spill-back on the metered on-ramps that activate the queue override. This resulted in 17.9% reduction on freeway delay. The analysis of field data on bottleneck discharge flows indicate that the proposed strategy may improve the freeway capacity by 5 to 10 percent. The delay on the parallel arterial was increased on the approaches feeding the on-ramps but decreased on the rest of the signal controlled approaches. The system-wide delay was reduced by 7 percent.