Study Details

Study Title: Evaluating the Safety Impact of Flashing Red Arrow Protected-Permissive Left-Turn Signal Control in Maryland

Authors: Rao et al.

Publication Date:JAN, 2019

Abstract: Maryland has used flashing red arrow (FRA) since the 1980’s at intersections operated with protected-permissive left-turn (PPLT) control, but impacts of this display on traffic safety have yet to be rigorously assessed. To evaluate the safety impacts of FRA and develop reliable guidelines this study has used data from 23 intersections in Maryland where the PPLT display was converted from a five-section (doghouse) cluster signal head with circular green to a three-section signal head with FRA and a supplemental sign. Safety Performance Functions (SPFs) calibrated for Maryland are developed on a sample of 20 intersections using PPLT display with circular green. Using the Empirical Bayes (EB) method, the results from the safety evaluation of FRA show that the respective crash modification factors (CMF) for left-turn crashes and total crashes were 0.53 and 0.75, thereby showing that FRA signals for PPLT control increase the safety at signalized intersections. Similarly, the CMFs for left-turn and total crashes resulting in injuries were found to be 0.63 and 0.71 respectively. Overall, among the 23 intersections, the left-turn crashes decrease by as much as 87%, and similar patterns were also observed for left-turn crashes resulting in injuries.

Study Citation: Rao, R.S., P.J. Rachtan, and G.L. Chang. "Evaluating the Safety Impact of Flashing Red Arrow Protected-Permissive Left-Turn Signal Control in Maryland". Presented at the 98th Annual Meeting of the Transportation Research Board, Paper No. 19-04784, Washington, D.C., (2019).

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Intersection traffic control

Countermeasure: Change from 5-section "doghouse" protected/permissive left turn to flashing red arrow protected/permissive left turn

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.53473 StarsLeft turnAllNot specifiedNot specified
0.63373 StarsLeft turnK,A,B,CNot specifiedNot specified
0.75253 StarsAllAllNot specifiedNot specified
0.71293 StarsAllK,A,B,CNot specifiedNot specified