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 |
|---|
| 0.445 | 55.5 |  | All | K,A,B,C | Not specified | Urban |
| 1.066 | -6.6 |  | All | All | Not specified | Urban and suburban |
| 0.37 | 63 | | All | K,A,B,C | Not specified | Urban and suburban |
| 0.759 | 24.1 | | All | All | Not specified | Urban and suburban |
| 0.338 | 66.2 | | All | K,A,B,C | Not specified | Urban and suburban |
| 0.792 | 20.8 | | All | All | Not specified | Urban and suburban |
| 0.342 | 65.8 | | All | K,A,B,C | Not specified | Urban and suburban |
| 0.809 | 19.1 | | All | All | Not specified | Urban and suburban |
| 0.288 | 71.2 | | All | K,A,B,C | Not specified | Urban and suburban |
| 0.735 | 26.5 | | All | All | Not specified | Urban and suburban |
| 0.451 | 54.9 | | 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 | | All | 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 | | All | 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 |  | All | 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 | | All | 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 | | All | All | Not Specified | Urban |
| 1.05 | -5 | | 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 | | All | 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 | | All | 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 | | All | 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 | | All | All | Not Specified | Urban |
| 0.84 | 16 | | Angle | All | Not Specified | Urban |
Countermeasure: Increase yellow change interval
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| 1.07 | -7.3 | | All | K,A,B,C | 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 | | All | All | Not Specified | Urban |
| 1.02 | -2 | | All | K,A,B,C | Not Specified | Urban |
Countermeasure: Install dynamic signal warning flashers
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| 0.814 | 18.6 | | All | All | Not Specified | All |
| 0.82 | 18 | | All | K,A,B,C | Not Specified | All |
| 0.956 | 4.4 | | Truck related | All | Not Specified | All |
