Study Details

Study Title: Safety Evaluation of Signal Installation With and Without Left Turn Lanes on Two Lane Roads in Rural and Suburban Areas

Authors: Srinivasan et al.

Publication Date: OCT, 2014

Abstract: Data from 117 intersections on two lane roads in rural and suburban areas in North Carolina were used to determine the safety effect of signalization with and without left turn lanes. This was a before-after study that was conducted using the empirical Bayes method. Before signalization, all the 117 intersections were controlled by stop signs on the minor legs. As part of implementing the empirical Bayes method, safety performance functions were estimated using data from a reference group of minor road stop controlled intersections. Results have been provided for three and four leg intersections separately. Five types of crashes were investigated: total, injury and fatal, rear end, frontal impact (type 1), and frontal impact (type 2). It is clear that the introduction of signals without the addition of left turn lanes resulted in a reduction in total crashes, injury and fatal crashes, and frontal impact crashes (both types), and an increase in rear end crashes. When left turn lanes were added, rear end crashes decreased as well. Injury and fatal crashes and rear end crashes benefited the most from the addition of left turn lanes. Overall, frontal impact crashes did not benefit from the addition of the left turn lanes. These results along with information about the cost of adding left and right turn lanes could be used by NCDOT to determine the locations where these turn lanes would be most cost-effective.

Study Citation: Srinivasan, R., B. Lan, and D. Carter. "Safety Evaluation of Signal Installation With and Without Left Turn Lanes on Two Lane Roads in Rural and Suburban Areas." Report No. FHWA/NC/2013-11. North Carolina Department of Transportation. Raleigh, North Carolina. (October 2014).

Related Citations: Srinivasan, R., D. Carter, and B. Lan. "Crash Modification Factors for Signal Installation With and Without Left Turn Lanes on Two Lane Roads in Rural and Suburban Areas." Presented at the Annual Meeting of the Transportation Research Board, Paper No. 17-03743, Washington, D.C., (2017).

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Intersection geometry

Countermeasure: Install left-turn lane

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.748 25.2 4 Stars All All Not specified All
0.924 7.6 3 Stars All All Not specified All
0.876 12.4 3 Stars All All Not specified All
0.566 43.4 4 Stars All K,A,B,C Not specified All
0.799 20.1 4 Stars All K,A,B,C Not specified All
0.744 25.6 4 Stars All K,A,B,C Not specified All
0.412 58.8 4 Stars Rear end All Not specified All
0.555 44.5 4 Stars Rear end All Not specified All
0.494 50.6 4 Stars Rear end All Not specified All
1.02 -2 3 Stars Other All Not specified All
0.879 12.1 3 Stars Other All Not specified All
0.916 8.4 3 Stars Other All Not specified All
1.086 -8.6 3 Stars Other All Not specified All
1.016 -1.6 3 Stars Other All Not specified All
1.046 -4.6 3 Stars Other All Not specified All

Category:Intersection traffic control

Countermeasure: Install a traffic signal

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.716 28.4 4 Stars All All Not specified All
0.614 38.6 4 Stars All All Not specified All
0.639 36.1 4 Stars All All Not specified All
0.601 39.9 4 Stars All K,A,B,C Not specified All
0.803 19.7 3 Stars All K,A,B,C Not specified All
0.642 35.8 4 Stars All K,A,B,C Not specified All
1.198 -19.8 3 Stars Rear end All Not specified All
1.586 -58.6 4 Stars Rear end All Not specified All
1.427 -42.7 4 Stars Rear end All Not specified All
0.46 54 4 Stars Other All Not specified All
0.413 58.7 4 Stars Other All Not specified All
0.42 58 4 Stars Other All Not specified All
0.492 50.8 4 Stars Other All Not specified All
0.415 58.5 4 Stars Other All Not specified All
0.426 57.4 4 Stars Other All Not specified All

Countermeasure: Install a traffic signal and left turn lanes

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.541 45.9 4 Stars All All Not specified All
0.569 43.1 4 Stars All All Not specified All
0.561 43.9 4 Stars All All Not specified All
0.465 53.5 4 Stars All K,A,B,C Not specified All
0.484 51.6 4 Stars All K,A,B,C Not specified All
0.48 52 4 Stars All K,A,B,C Not specified All
0.505 49.5 4 Stars Rear end All Not specified All
0.892 10.8 3 Stars Rear end All Not specified All
0.487 51.3 4 Stars Other All Not specified All
0.365 63.5 4 Stars Other All Not specified All
0.387 61.3 4 Stars Other All Not specified All
0.711 28.9 4 Stars Rear end All Not specified All
0.55 45 4 Stars Other All Not specified All
0.424 57.6 4 Stars Other All Not specified All
0.448 55.2 4 Stars Other All Not specified All