Study Details

Study Title: Safety of Special Time-of-Day Protected/Permitted Left-Turn Signal Control Display

Authors: Ozmen et al.

Publication Date:JAN, 2009

Abstract: This paper provides a safety evaluation of a special protected/permitted left turn signal control that has been implemented in the urbanized area of Las Vegas, Nevada. The special left turn display provides protected only left turns during certain times of day by suppressing the permitted green ball and yellow ball displays. During other time periods, the signal resumes standard five-section protected/permitted operations. This special operation allows the use of lead-lag phasing during protected only control to improve progression and standard protected/permitted control for improving capacity and minimizing delays during low-volume time periods. Before and after studies were conducted using the crash data from 10 intersections that have implemented the special left-turn display. Results from the analyses indicated that there is no apparent increase in crashes, thus indicating no obvious safety concerns due to use of the special display.

Study Citation: Ozmen, O., Z.Z. Tian, and R. Gibby, "Safety of Special Time-of-Day Protected/Permitted Left-Turn Signal Control Display." TRB 88th Annual Meeting Compendium of Papers CD-ROM, #09-2074. Washington, D.C., (2009).

Related Citations: Ozmen, O., Z.Z. Tian, and R. Gibby, "Safety of the Las Vegas left-turn display". Accident Analysis and Prevention, Vol. 62, (2014) pp. 95-101.

CMFs Associated With This Study

Category: Intersection traffic control

Countermeasure: Change from protected/permitted to protected only left turn signal control during special time-of-day (left turn crashes)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.5841.5text textAllAllNot SpecifiedUrban