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Evaluation of Intersection Safety and Capacity Relevant to Signal Timing on Arizona’s State Highway System
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2024-09-01
[PDF-2.42 MB]
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Edition:Final Report
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Abstract:Traffic signal phase-change intervals are intended to provide a safe transition between two conflicting signal phases or a right-of-way transition between conflicting road-user movements. As a result, signal phase change (includes yellow change interval, red-clearance interval, and pedestrian intervals) has significant safety and operations implications at signalized intersections. Currently, there is no national standard for calculating these durations. Additionally, the current ADOT-recommended practice for calculating traffic signal intervals has resulted in two issues: (1) lengthy red-clearance intervals at interchanges with large conflict areas; and (2) yellow change interval durations with the potential of not meeting the needs of the driver population. The objectives of this research were to: (1) evaluate ADOT’s current signal timing design guidelines; and (2) recommend an optimal signal timing design for the Arizona state highway system. A comprehensive evaluation of the effects of the current signal timing design guidelines and a thorough pilot study were used to inform a set of recommendations. These recommendations were used to draft a proposed version of the ADOT’s Guidelines and Processes, which describes the interval duration calculation methods. Proposed changes to the methods include (1) an increase in the approach speed used to calculate left-turn yellow-change intervals; (2) an increase in the intersection speed used to calculate the red-clearance intervals at single-point urban interchanges; and (3) a decrease in the walk speed used to compute “DON’T WALK” interval durations at locations with a high volume of slower-moving pedestrians. These changes would yield increased yellow-change intervals, decreased red-clearance intervals, and longer “DON’T WALK” intervals.
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