The Effects of Left-turn Lane Queue Lengths on Intersection Delay

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Conference Proceeding

Publication Date



The intersection delay, representing the levels of service, is the major performance measure of a signalized intersection. The most popular traffic software packages such as Highway Capacity Software (HCS) and Synchro provide detail delay calculation, level of service analyses, and queue analyses. However, the effects of available queue storage lengths of turn lanes on intersection delay were not addressed in the HCS and Synchro Version 5. The software packages reported identical results of lane group delays, regardless of the inputted turn lane queue storage lengths. Recently, Synchro Version 6 started to introduce a new series of traffic analysis to address how queue can reduce capacity and increase delay through spillback, starvation, and storage blockage between lane groups. The focuses of this study are to examine the storage blockage problem for left-turn lanes at signalized intersections, and provide potential strategies to reduce traffic congestion and improve traffic safety. This paper first examines the effects of inadequate left-turn queue storage lengths on intersection delay. Then, it describes the importance of addressing left-turn lane storage blockage problems. The methods to measure the performance of signalized intersections with inadequate left-turn lane queue storage lengths are then presented. This paper develops effective strategies in order to minimize negative traffic operational impact resulted from inadequate left-turn lane length. These strategies are illustrated by examples with microscopic simulation results from the SimTraffic. The paper also provides transportation professionals potential strategies to alleviate traffic congestion and safety problems caused by inadequate left-turn lane storage lengths at signalized intersections.

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Citation / Publisher Attribution

ITE 2004 Annual Meeting and Exhibit, Compendium of Technical Papers, Washington, D.C., August 2004.