Traffic characteristics of protected/permitted left-turn signal displays

25 p. ; Prepared for the 79th Annual Meeting of the Transportation Research Board, Washington, D.C. January, 2000At least four variations of the permitted indication in protected/permitted left-turn (PPLT) control have been developed in an attempt to improve the level of driver understanding and safety. These variations replace the green ball permitted indication with a flashing red ball, a flashing yellow ball, a flashing red arrow, or a flashing yellow arrow indication. In addition, the "Manual on Uniform Traffic Control Devices" allows several PPLT signal display arrangements. The variability in indication and arrangement has led to a myriad of PPLT displays throughout the United States. The level of driver understanding related to each PPLT display type, and the associated impact on traffic operations and safety, has not been quantified. A study was conducted to evaluate the operational characteristics associated with different PPLT signal displays. Specifically, the study quantified saturation flow rate, start-up lost time, response time, and follow-up headway associated with selected PPLT displays. No differences in saturation flow rate and start-up lost time were found due to the type of PPLT signal display. Saturation flow rates ranged from 1,770 to 2,400 vehicles per hour of green per lane and were related to differences in driver behavior between geographic locations. The variation in start-up lost time and response time between locations was primarily related to differences in phase sequence. The flashing red permitted indications were associated with the longest follow-up headway times, since drivers are required to stop before turning left with a flashing red permitted indication. The shortest follow-up headway was associated with the five-section cluster display using a green ball indication

Traffic conflicts associated with protected/permitted left-turn signal displays

25 p. ; Paper prepared for the 79th Annual Meeting of the Transportation Research Board, Washington, D.C. January 2000.Several different protected/permitted left-turn (PPLT) signal displays are used in the United States, varying in configuration and permitted indication. Questions remain as to the safety implications of using each type of display. Since left-turn crash data do not contain information related to the type of signal display and permitted indication at the intersection, conflict studies are often used as a surrogate measure. This paper describes a study of 24 intersections in eight U.S. cities to evaluate traffic conflicts and events (safety implications) associated with selected PPLT signal displays. Based on the results of this study, there was no difference in the conflict rates associated with the PPLT signal displays evaluated. Conflict rates varied from 0.0 to 1.4 conflicts/1,000 entering vehicles. Conflicts attributed to driver misunderstanding of the signal display or indication were primarily associated with the green ball permitted indication. Most left-turn events were related to hesitation at the onset of the protected green arrow indication. Evaluating each event type individually suggested that the five-section horizontal display with both the green arrow and red ball illuminated was associated with a significantly higher rate of Type 1 (hesitate on green arrow indication) events. Currently, the Manual on Uniform Traffic Control Devices (MUTCD) requires simultaneous illumination of the green arrow and adjacent through movement indication in the PPLT signal display during the protected left-turn phase. This result demonstrated the increase in signal display complexity and driver workload with the simultaneous illumination of the green arrow and red ball indications

Traffic control guidelines for urban arterial work zones. Volume I: Executive summary. Final report.

Texas Department of Transportation, AustinFederal Highway Administration, Washington, D.C.Mode of access: Internet.Author corporate affiliation: Texas Transportation Institute, College StationReport covers the period Sept 1989 - Aug 1991Subject code: CCCCSubject code: CDNCSubject code: HBSubject code: KBMSubject code: YE

Use of protected/permitted left-turn signal control in the U.S.

14 p. ; Paper prepared for Transportation Frontiers for the Next Millennium: 69th Annual Meeting of the Institute of Transportation Engineers, Las Vegas, Nevada, August 1-4, 1999.The growing level of traffic demand on urban and rural roadways has led to increased use of protected/permitted left-turn (PPLT) signal control. PPLT signal phasing provides an exclusive phase for left turns as well as a permissive phase during which left turns can be made if gaps in opposing through traffic allow, all within the same signal cycle. The signal display most commonly used with PPLT signal phasing is a five-section signal display with a green arrow indication for the exclusive left-turn phase and a green ball for the permitted left-turn phase. However, many transportation agencies use different mounting locations, signal display arrangements, and permitted indications when implementing PPLT. In addition, there are at least four variations of the permitted indication, including the flashing red ball, flashing red arrow, flashing yellow ball, and flashing yellow arrow. This paper presents the results of a comprehensive agency survey sent to local, county, and state officials designed to determine the use of PPLT signal control in the United States. The first section presents general survey information, including the total number of surveys received and the total number of signalized intersections reported. This section also quantifies the number of signalized intersections containing PPLT signal displays. The second section presents the types of PPLT signal displays used by these agencies and typical signal display mounting practices. The third section presents intersection geometry and signal phasing practices most often used with PPLT signal phasing. Finally, the last section provides a brief summary of the results

Evaluation of flashing traffic signal operation. Final report.

Texas Department of Transportation, AustinTransportation Department, Washington, D.C.Mode of access: Internet.Author corporate affiliation: Texas Transportation Institute, College StationReport covers the period Sept 1991 - Aug 1993Subject code: CIFSubject code: HBESubject code: NKF