Beth Taylor

Randy B. Machemehl

Development and Evaluation of Light Rail Transit Signal Priority Strategies

Gye-Hyeong Ahn

A traffic simulation model was developed to provide a methodology for traffic signal timing in oversaturated urban arterial networks. Two control objectives of traffic signal timing in oversaturated conditions were taken into consideration. One was to maximize the number of vehicles processed in an arterial network, which has an oversaturated traffic demand at the entry of the arterial street and moderate traffic demands at the entry of cross streets. The other was to prevent queue spillback or to minimize the occurrence of queue spillback if inevitable. Signal timing offset was the dominant factor affecting system performance; although, link length was also important. When link length is short, the optimum offset is approximately zero, regardless of the cycle length. As link length increases beyond the minimum 200 ft (61 m) tested, for highest efficiency, downstream intersection greens should begin before upstream intersection greens. This relationship, opposite to conventional progression greens, moves downstream queues before incoming platoon arrival. Cross street traffic operations can have significant effects upon arterial performance and system efficiency. System efficiency rapidly deteriorates when any cross street green becomes too short for the link length. Therefore, a "practical" minimum green interval for cross streets is necessary to accommodate upstream cross street through traffic and turning vehicles from the arterial. When the cross street green is shorter than the minimum, even with the best offset combination, queue spillbacks occur on the cross streets and system efficiency deteriorates.

Randy B. Machemehl

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