TRB’s National Cooperative Highway Research Program (NCHRP) Report 705: Evaluation of Safety Strategies at Signalized Intersections explores crash modification factors (CMFs) for safety strategies at signalized intersections. CMFs are a tool for quickly estimating the impact of safety improvements. 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 before-after 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. (Author/publisher) This report is available online at http://www.trb.org/Publications/Blurbs/165938.aspx
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