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NCHRP Project 17-35: Evaluation of Safety Strategies at Signalized Intersections



Evaluations of Low Cost Safety Improvements Pooled Fund Study



Crash reduction factors (CRFs) or accident reduction factors (ARFs) provide a quick way for transportation agencies to estimate crash reductions associated with highway safety improvements. Many States and local jurisdictions use these factors to make program–planning decisions about implementing specific treatments and/or to quickly determine the costs and benefits of selected alternatives. Related to CRFs are accident modification factors (AMFs) and crash modification factors (or CMFs). CRFs are the quantitative results from research studies, indicating the percentage reductions in crashes that can be expected after implementing treatments or programs. Derived from CRFs, AMFs are used in predictive methodologies to estimate the reduction in crashes that can be expected for a specific treatment or installation. AMFs are often expressed in the form of (1–CRF); therefore a CRF of 15 percent would be represented as an AMF value equal to 0.85.

To achieve the greatest return on investment when choosing between alternative treatments, State and municipal AMF accuracy is important. The availability of more reliable AMFs also may be used in developing broad–based local and State policy decisions related to project planning and design.

The objective of this ongoing NCHRP project is to improve the quality of existing AMFs and to develop additional AMFs (or perhaps functions) to fill current voids. The first phase of this research study included a critical review of existing literature to document the best available AMFs, and a survey of State departments of transportation to determine the applicability of existing AMFs and priorities for new or improved AMFs. The results of the first phase were documented in a research results digest, which will be published later this year. The digest includes: 1) an AMF knowledge matrix that provides a status report on the quality of AMFs for a large number of treatments, 2) summaries of the AMFs that are considered credible at the time of the study, and 3) a discussion of other ongoing research efforts aimed at improving AMFs. The digest will be posted at the following Web address: