Browsing by Subject "Flashing traffic signals"

Now showing 1 - 3 of 3
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    Development of Guidelines for Permitted Left-Turn Phasing Using Flashing Yellow Arrows.
    (Minnesota Department of Transportation, 2015-06) Davis, Gary A.; Hourdos, John; Moshtagh, Vahid
    The objective of this project was to develop guidelines for time-of-day use of permitted left-turn phasing, which can then be implemented using flashing yellow arrows (FYA). This required determining how the risk for left-turn crashes varied as traffic-flow conditions varied during the course of a representative day. This was accomplished by developing statistical models, which expressed the risk of occurrence of a left-turn crash during a given hour as a function of the left-turn demand, the opposing traffic volume, and a classification of the approach with respect to the opposing traffic speed limit, the type of left-turn protection, and whether or not opposing left-turn traffic could obstruct sight distance. The models were embedded in a spreadsheet tool which will allow operations personnel to enter, for a candidate intersection approach, existing turning movement counts, and a classification of the approach with respect to speed limit, turn protection, and sight distance issues and receive a prediction of how the risk of left-turn crash occurrence varies throughout the day, relative to a user-specified reference condition.
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    Driver Comprehension of Flashing Yellow Arrows
    (Minnesota Department of Transportation, 2023-12) Davis, Gary A.; Stern, Raphael; Duhn, Melissa; Gao, Jingru
    In 2009, the FHWA's Manual on Uniform Traffic Control Devices (MUTCD) introduced the flashing yellow arrow (FYA) traffic signal as an alternative to circular green (CG) to indicate permitted left turns. The FYA is arguably a more intuitive indication that left turns are permitted but not protected and, in addition, the FYA signal heads can support time-of-day changes between protective and permissive left -turn phasing. In 2019, a Research Needs Statement stated that "Research is needed to examine driver comprehension of flashing yellow arrows in different light arrangements and the role of signage." Our objective in this project was to assess drivers' understanding of FYA signal indications and to see if the presence or absence of "Left Turn Yield" signs affect gap acceptance. This was accomplished by conducting an online survey of drivers regarding their understanding of FYA signals and by carrying out a field study of drivers' gap acceptance at a set of Twin Cities intersections.
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    Estimating the Crash Reduction and Vehicle Dynamics Effects of Flashing LED Stop Signs
    (Minnesota Department of Transportation, 2014-01) Davis, Gary A.; Hourdos, John; Xiong, Hui
    A flashing LED stop sign is essentially a normal octagonal stop sign with light emitted diodes (LED) on the stop sign’s corners. A hierarchical Bayes observational before/after study found an estimated reduction of about 41.5% in right-angle crashes, but with 95% confidence this reduction could be anywhere between 0% and 70.8%. In a field study, portable video equipment was used to record vehicle approaches at an intersection before and after installation of flashing LED stop signs. After installing the flashing stop signs, there was no change in the relative proportion of clear stops to clear non-stops when minor approach drivers did not face opposing traffic, but the relative proportion of clear stops increased for drivers who did encounter opposing traffic. Random samples of 60 minor approach vehicles were selected before and after installation of flashing LED stop signs and speeds for these vehicles when about 500 feet from the intersection, and average deceleration rates over the final 500 feet, were estimated using trajectory-based methods. Average approach speeds tended to be highest in June, somewhat lower in July, and lower yet in September and November, with September and November having roughly equal average speeds. The average deceleration rates showed a similar pattern.