SPR 14-481 Permitted Left Turn Guide

Grants and Contracts Details


A fundamental objective of traffic signals is the development of signal plans that could improve efficiency of operations and reduce delays. An issue that is of concern is the potential for increased delays for protected only phases when it is possible to accommodate them through a combination of protected-permitted phasing. Another issue is the use of permitted phasing in lieu of protected phasing at certain times of the day when the demand is lower than peak periods. In this case, using a permitted phase at night (e.g. 11:00 pm to 5:00 am) will reduce delays and has the potential to improve safety since drivers may avoid taking unnecessary risks due to prolonged waiting for a green indicator. The primary objective of this research is to determine any potential changes to existing practices and policies with regards to permitted left-turn phasing to improve vehicular efficiency. This research will provide a guide that will lay the foundation for a more responsive evaluation and implementation of left-turn accommodation at signalized intersections aiming to improve flow and reduce delays. It is expected that the results will be used to improve flow and reduce delays by creating a more appropriate and traffic-responsive system while considering time of day flow variations and demands. The anticipated benefits are expected to include lower delays for traffic, potential safety improvements, and a more robust left-turn evaluation and accommodation policy.
Effective start/end date7/1/136/30/14


  • KY Transportation Cabinet


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