Study Details

Study Title: Evaluation of Safety Strategies at Signalized Intersections

Authors: Srinivasan, et al.

Publication Date: 2011

Abstract: Crash modification factors (CMFs), also known as Accident modification factors, provide a computationally simple and quick way of estimating crash reductions. Many states and local agencies have a set of CMFs that are used for estimating the safety impacts of various types of engineering improvements. Typically, these factors are computed using beforeafter comparisons, although recent research also has suggested the use of cross-sectional comparisons. Currently, CMFs are often used in program planning to make decisions concerning whether to implement a specific treatment and/or to quickly determine the costs and benefits of selected alternatives. CMFs are also used in project development for nonsafety as well as safety-specific projects and could be used by agencies in deciding on policies affecting general project design (e.g., context-sensitive design solutions and traffic calming). CMFs are also key components of the latest safety-estimation tools and procedures, including the Interactive Highway Safety Design Model, SafetyAnalyst, and the procedures in the AASHTO Highway Safety Manual. NCHRP Project 17-18(3) developed a series of guides to assist state and local agencies in reducing injuries and fatalities in targeted emphasis areas. Each guide includes a brief introduction, a general description of the problem, strategies to address the problem, and a model implementation process. NCHRP Report 500, Volume 12: Guidance for Implementation of the AASHTO Strategic Highway Safety Plan, A Guide for Reducing Collisions at Signalized Intersections includes strategies for improving the safety of signalized intersections. However, the safety effectiveness of many of the strategies in the guide have not been rigorously evaluated. Under NCHRP Project 17-35, "Evaluation of Safety Strategies at Signalized Intersections," researchers at the University of North Carolina Highway Safety Research Center developed reliable CMFs for a number of safety strategies outlined in NCHRP Report 500, Volume 12. The research team reviewed the literature and ongoing research related to CMF development, surveyed the state DOTs, and developed a priority list of treatments deemed to be important in safety decisions. The final list was determined based on the availability of data needed in CMF development. CMFs were developed for the installing dynamic advanced warning flashers, converting signalized intersections to roundabouts, increasing clearance intervals, changing left-turn phasing, and introducing flashing yellow arrow. Users are encouraged to consider the quality and applicability of CMFs when selecting a CMF for use in the decision-making process. Users are also encouraged to consider the measures of uncertainty (standard error or standard deviation) associated with a given CMF. The details of each evaluation are included in the appendices. The appendices are posted on the TRB project website at http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp? ProjectID=461.

Study Citation: Srinivasan, R., Baek, J., Smith, S., Sundstrom, C., Carter, D., Lyon, C., Persaud, B., Gross, F., Eccles, K., Hamidi, A., and Lefler, N., "NCHRP Report 705: Evaluation of Safety Strategies at Signalized Intersections.", Washington, D.C., Transportation Research Board, National Research Council, (2011)

Related Citations: 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 geometry

Countermeasure: Convert signalized intersection to modern roundabout

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.792 20.8 4 Stars All All Not specified Urban and suburban
0.342 65.8 4 Stars All K,A,B,C Not specified Urban and suburban
0.809 19.1 4 Stars All All Not specified Urban and suburban
0.288 71.2 4 Stars All K,A,B,C Not specified Urban and suburban
0.735 26.5 3 Stars All All Not specified Urban and suburban
0.451 54.9 3 Stars All K,A,B,C Not specified Urban and suburban
0.576 42.4 4 Stars All All Not specified Suburban
0.259 74.1 4 Stars All K,A,B,C Not specified Suburban
1.15 -15 3 Stars All All Not specified Urban
0.445 55.5 4 Stars All K,A,B,C Not specified Urban
1.066 -6.6 3 Stars All All Not specified Urban and suburban
0.37 63 3 Stars All K,A,B,C Not specified Urban and suburban
0.759 24.1 4 Stars All All Not specified Urban and suburban
0.338 66.2 3 Stars All K,A,B,C Not specified Urban and suburban

Category:Intersection traffic control

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

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.031 -3.1 4 Stars All All Not specified Urban
0.962 3.8 4 Stars All K,A,B,C Not specified Urban
0.862 13.8 4 Stars Left turn All Not specified Urban
1.075 -7.5 4 Stars Rear end All Not specified Urban

Countermeasure: Changing left turn phasing from at least one permissive approach to flashing yellow arrow (FYA)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.753 24.7 5 Stars All All Not Specified Urban
0.635 36.5 5 Stars Left turn All Not Specified Urban

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

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.338 -33.8 5 Stars All All Not Specified Urban
2.242 -124.2 5 Stars Left turn All Not Specified Urban

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

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.922 7.8 4 Stars All All Not Specified Urban
0.806 19.4 4 Stars Left turn All Not Specified Urban

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

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.958 4.2 4 Stars All All Not Specified Urban
0.914 8.6 4 Stars All K,A,B,C Not Specified Urban
0.787 21.3 4 Stars Left turn All Not Specified Urban
1.05 -5 4 Stars Rear end All Not Specified Urban

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

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.081 -8.1 4 Stars All All Not Specified Urban
0.995 0.5 4 Stars All K,A,B,C Not Specified Urban
0.925 7.5 4 Stars Left turn All Not Specified Urban
1.094 -9.4 4 Stars Rear end All Not Specified Urban

Countermeasure: Increase all red clearance interval

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.798 20.2 4 Stars All All Not Specified Urban
0.863 13.7 3 Stars All K,A,B,C Not Specified Urban
0.804 19.6 3 Stars Rear end All Not Specified Urban
0.966 3.4 3 Stars Angle All Not Specified Urban

Countermeasure: Increase total change interval (greater than ITE recommended practice)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.922 7.8 3 Stars All All Not Specified Urban
0.937 6.3 3 Stars All K,A,B,C Not Specified Urban
0.643 35.7 4 Stars Rear end All Not Specified Urban
1.068 -6.8 3 Stars Angle All Not Specified Urban

Countermeasure: Increase total change interval (remains less than ITE recommended practice)

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.728 27.2 3 Stars All All Not Specified Urban
0.662 33.8 3 Stars All K,A,B,C Not Specified Urban
0.848 15.2 3 Stars Rear end All Not Specified Urban
0.84 16 3 Stars Angle All Not Specified Urban

Countermeasure: Increase yellow change interval

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.14 -14.1 3 Stars All All Not Specified Urban
1.07 -7.3 3 Stars All K,A,B,C Not Specified Urban
0.934 6.6 3 Stars Rear end All Not Specified Urban
1.076 -7.6 3 Stars Angle All Not Specified Urban

Countermeasure: Increase yellow interval and add all red interval

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.99 1 3 Stars All All Not Specified Urban
1.02 -2 3 Stars All K,A,B,C Not Specified Urban
1.12 -11.7 3 Stars Rear end All Not Specified Urban
0.961 3.9 3 Stars Angle All Not Specified Urban

Countermeasure: Install dynamic signal warning flashers

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.814 18.6 4 Stars All All Not Specified All
0.792 20.8 4 Stars Rear end All Not Specified All
0.745 25.5 4 Stars Angle All Not Specified All
0.82 18 4 Stars All K,A,B,C Not Specified All
0.956 4.4 3 Stars Truck related All Not Specified All