Study Details

Study Title: Crash Modification Factors for Changing Left Turn Phasing

Authors: Srinivasan et al.

Publication Date:JAN, 2012

Abstract: This study estimated crash modification factors (CMFs) from before-after evaluations of two treatments targeted at left turn crashes at signalized intersections: (1) changing from permissive to protected-permissive phasing, and (2) implementation of flashing yellow arrow (FYA) for permissive left turns. Results of the first evaluation, which was based on 59 intersections from Toronto and 12 from North Carolina, indicated a substantial reduction in left turn opposing through crashes, especially at intersections where more than one leg was treated, and a small percentage increase in rear end crashes. For the second evaluation (FYA), which was based on data from 51 signalized intersections from Oregon, Washington, and North Carolina, results indicated a safety benefit at locations with some kind of permissive left turn operation before, and a disbenefit where there was protected only operation before. A key aspect of the study was the estimation of the standard deviation of the distribution of the CMF in addition to the conventionally estimated standard error of the mean CMF value. For several CMFs, the standard deviation of the distribution was larger than the standard error of the mean value of the CMF, indicating substantial variation in the treatment effect across sites. This indicates the need for further research into the development of crash modification functions instead of crash modification factors, and for the use of large treatment databases to undertake more extensive disaggregate analysis of safety effects. Equally important, it emphasizes the importance of providing more explicit consideration of CMF variability in future editions of the Highway Safety Manual.

Study Citation: Srinivasan, R.; Lyon, C.; Persaud, B.; Baek, J.; Gross, F.; Smith, S.; Sundstrom, C. A. " Crash Modification Factors for Changing Left Turn Phasing." Presented at the Transportation Research Board 91st Annual Meeting, Paper No. 12-2521, January 22-26, 2012, Washington, DC.

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Intersection traffic control

Countermeasure: Change permissive left-turn phasing to protected/permissive

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.031-3.14 StarsAllAllNot specifiedUrban
0.9623.84 StarsAllK,A,B,CNot specifiedUrban
0.86213.84 StarsLeft turnAllNot specifiedUrban
1.075-7.54 StarsRear endAllNot specifiedUrban
1.033-3.34 StarsAllAllNot specifiedUrban
0.9584.24 StarsAllK,A,B,CNot specifiedUrban
0.85814.24 StarsLeft turnAllNot specifiedUrban
1.063-6.34 StarsRear endAllNot specifiedUrban
1.015-1.53 StarsAllAllNot specifiedUrban
0.9950.53 StarsAllK,A,B,CNot specifiedUrban
0.86513.53 StarsLeft turnAllNot specifiedUrban
1.236-23.63 StarsRear endAllNot specifiedUrban

Countermeasure: Changing left turn phasing from permissive on one leg and protected-permissive on another leg to flashing yellow arrow (FYA)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.82717.33 StarsAllAllNot specifiedUrban
0.9118.93 StarsAllK,A,B,CNot specifiedUrban
1.058-5.83 StarsRear endAllNot specifiedUrban
0.63836.23 StarsLeft turnAllNot specifiedUrban
0.58641.43 StarsLeft turnAllNot specifiedUrban

Countermeasure: Changing left turn phasing from permissive to flashing yellow arrow (FYA)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.40459.63 StarsAllAllNot specifiedUrban
0.58423 StarsLeft turnAllNot specifiedUrban
0.52947.13 StarsLeft turnAllNot specifiedUrban

Countermeasure: Changing left turn phasing from protected to flashing yellow arrow (FYA)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.187-18.73 StarsAllAllNot SpecifiedUrban
2.043-104.34 StarsLeft turnAllNot SpecifiedUrban
2.073-107.34 StarsLeft turnAllNot SpecifiedUrban
1.509-50.94 StarsAllAllNot SpecifiedUrban
1.479-47.93 StarsAllK,A,B,CNot SpecifiedUrban
1.752-75.23 StarsRear endAllNot SpecifiedUrban
2.683-168.33 StarsLeft turnAllNot SpecifiedUrban
3.696-269.63 StarsLeft turnAllNot SpecifiedUrban

Countermeasure: Changing left turn phasing from protected-permissive to flashing yellow arrow (FYA)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.56343.73 StarsLeft turnAllNot SpecifiedUrban
0.9544.63 StarsAllAllNot SpecifiedUrban
0.75224.83 StarsAllK,A,B,CNot SpecifiedUrban
1.344-34.43 StarsRear endAllNot SpecifiedUrban
0.82183 StarsLeft turnAllNot SpecifiedUrban
0.7303 StarsLeft turnAllNot SpecifiedUrban
0.83816.23 StarsAllAllNot SpecifiedUrban
0.76223.83 StarsLeft turnAllNot SpecifiedUrban

Countermeasure: Changing left turn phasing on more than one approach from permissive to protected-permissive

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.9455.53 StarsAllAllNot SpecifiedUrban
0.87812.24 StarsAllK,A,B,CNot SpecifiedUrban
0.76223.84 StarsLeft turnAllNot SpecifiedUrban
1.021-2.13 StarsRear endAllNot SpecifiedUrban
1.023-2.33 StarsAllAllNot SpecifiedUrban
1.057-5.73 StarsAllK,A,B,CNot SpecifiedUrban
0.83416.63 StarsLeft turnAllNot SpecifiedUrban
1.261-26.13 StarsRear endAllNot SpecifiedUrban

Countermeasure: Changing left turn phasing on one approach from permissive to protected-permissive

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.085-8.54 StarsAllAllNot SpecifiedUrban
1.005-0.53 StarsAllK,A,B,CNot SpecifiedUrban
0.9198.13 StarsLeft turnAllNot SpecifiedUrban
1.091-9.14 StarsRear endAllNot SpecifiedUrban
0.9851.53 StarsAllAllNot SpecifiedUrban
0.81518.53 StarsAllK,A,B,CNot SpecifiedUrban
0.9287.23 StarsLeft turnAllNot SpecifiedUrban
1.128-12.83 StarsRear endAllNot SpecifiedUrban