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Summary:Use of the flashing yellow arrow indication for permissive left-turn control has become more common in the U.S. since it was adopted in the 2009 Edition of the Manual on Uniform Traffic Control Devices. A complete understanding of the safety implications at signalized intersections is critically important. This paper examines the results of a permissive left-turn driver behavior study conducted in a high fidelity driving simulator. The experimental results suggest 1) that when there are more pedestrians present in the conflicting crosswalk, the driver's average fixation duration on crossing pedestrians is greater than when there is minimal pedestrian activity; 2) that 4% to 7% of drivers do not fixate on pedestrians in the crosswalk when completing their left turn; and 3) that 39% of drivers do not fixate on likely pedestrian locations when pedestrians are not present.

Many jurisdictions are using the flashing yellow arrow (FYA) to control protected and permissive left turns. For cost and other reasons, some jurisdictions have or are considering implementing FYA with a three-section vertical head, displaying the flashing yellow indication in the same signal face as the protected green arrow. The current Manual on Uniform Traffic Control Devices permits the operation of a three-section vertical head only for permissive turns in locations where heights are restricted. This paper summarizes a comparison of driver performance with three- and four-section FYA signal configurations gathered in a high-fidelity, motion-based driving simulator with mobile eye-tracking equipment. The experiment controlled for the effects of the opposing traffic, the presence and walking direction of pedestrians, and the signal head arrangement. A 24-intersection simulated environment was created, and 27 subjects completed the course, producing 620 permissive left-turn maneuvers for further analysis. Driver performance was measured from the (a) average total eye glance durations at specific areas of interest and (b) the position of the pedestrian in the crosswalk when the driver initiated the left turn. No statistically significant differences between the average fixation duration when the FYA was presented with a three- or four-section signal head were identified. The pedestrian's position in the crosswalk when the driver began the left turn was not statistically significantly different for three of the four pedestrian walking directions presented. Overall, measurable driver performance does not seem to be sensitive to the vertical positioning of the FYA display in the permissive interval.

This research documents the operational benefits of additional phases, barrier bars, and a call-based transit priority signal-phasing strategy over a more traditional eight-phase, two-barrier preemption-based transit signal–phasing strategy. The call-based timing strategy, with a more flexible ring-and-barrier structure, takes advantage of additional phases to run less-impactful transit prioritization for light-rail trains. These two strategies have been field implemented in Portland, Oregon, at the signalized intersection of Southwest Porter Street and Southwest Moody Avenue, an intersection that has distinct signalized movements for the private-automobile, streetcar, light-rail train, bus, pedestrian, and bicycle modes. The operations of the two-intersection signal-phasing strategies were evaluated and tested by using hardware and software-in-the-loop microsimulation (in Vissim) to isolate the expected change in operational efficiency in modal delay. The two-barrier preemption-based transit signal-phasing strategy showed high variability in delay for certain movements, in particular, pedestrians. The call-based phasing strategy with flexible ring-and-barrier structure reduced total and average intersection delay. This research shows that the call-based phasing strategy with flexible ring-and-barrier structure can provide a less disruptive transit prioritization. Agencies should consider the call-phased transit priority strategy over the more traditional preemption-based strategy at a signalized intersection when ( a) delaying potential preemptive movements mode will not have large safety effects, ( b) pedestrian demand is high, ( c) preemption service will be frequent, or ( d) the intersection is operating at or over capacity.