Left-turn movements at an intersection affect the capacity of that intersection. As the left-turning volume at an intersection continues to grow, the green time required to meet the left-turn demand increases. This, in turn results in longer cycle lengths. Also with the increase in the left-turn volume, the queues lengthen resulting in greater storage length requirements. The combinations of these effects tend to increase delay at the intersection and lower the level of service. Installation of multiple left-turn lanes (dual and triple) can result in the reduction of vehicle queue lengths, delays and left-turn storage length. Dual and triple left-turn lanes require less green time compared to single left-turn lanes to meet the left-turning vehicle demand. This saving in the green time can be allocated to the other operations at the intersection thus resulting in the increase of intersection capacity. The installation of these multiple left-turn raises questions for which the Missouri Department of Transportation (MoDOT) has not yet developed answers. Specifically, MoDOT seeks guidance on: (1) Criteria for determining when to install double and triple left-turns; (2) The type of phasing to be used for dual and triple left-turn lanes; (3) Whether to use 'Dallas' or permitted lead-lag phasing for any left-turn lanes; and (4) Where to begin reducing the number receiving lanes downstream of an intersection with multiple left-turn lanes. This study uses a combination of literature review and a nationwide survey of state practice to provide answers to these questions.
Assessment of Multiple Left-Turn Phasing Strategies
2003
50 pages
Report
No indication
English
Transportation & Traffic Planning , Transportation , Road Transportation , Left turn lanes , Missouri , Turning lanes , Traffic capacity , Literature review , Surveys , Highway planning , Traffic lanes , Left turns , Multiple left turn lanes , Traffic signal phasing , Dallas phasing , Permissive phasing , Protected phasing
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