Abstract
The aim of this research was to develop operational strategies for integrating the operations between diamond interchange traffic signals and ramp metering signals. Integrated operational strategies were developed on the basis of the two commonly used diamond interchange phasing schemes: the basic three-phase scheme and the Texas Transportation Institute four-phase scheme. The key elements of the integration system and its operations include a proposed enhanced detection system and an operational algorithm. Through implementation of special signal timings at the diamond interchange, the traffic flows feeding the ramp meters can be effectively controlled and thus minimize ramp queues and the resulting need to flush the queues, which would possibly lead to freeway breakdown. The operational strategies were evaluated with VISSIM microscopic simulation under three general traffic demand scenarios–-low, medium, and high–-as characterized by the volume-to-capacity ratios at the metered ramps. The results of the evaluation indicated that the integrated operations were most effective under a medium traffic demand scenario in preventing or delaying the onset of ramp metering queue flush, thereby reducing freeway breakdown and system delays.
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