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(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
---|---|---|---|---|---|---|
0.53 | 47 | Left turn | All | Not specified | Not specified |
0.63 | 37 | Left turn | K,A,B,C | Not specified | Not specified |
0.75 | 25 | All | All | Not specified | Not specified |
0.71 | 29 | All | K,A,B,C | Not specified | Not specified |