Crash Reduction Factors
A crash reduction factor (CRF) is the percentage crash reduction that might be expected after implementing a given countermeasure at a specific site. For example, the installation of centerline rumble strips on a two-lane roadway can expect a 14% reduction in all crashes and a 55% percent reduction in head-on crashes.
Expected countermeasure effectiveness is also commonly expressed as a crash modification factor (CMF). A CMF is a multiplicative factor used to compute the expected number of crashes after implementing a given countermeasure at a specific site.
Both CRFs and CMFs are commonly used in the field of traffic safety and are related by a simple mathematical formula: CMF = 1 - (CRF/100). For example, if a particular countermeasure is expected to reduce the number of crashes by 23% (i.e., the CRF is 23), the CMF will be 1 - (23/100) = 0.77. On the other hand, if the treatment is expected to increase the number of crashes by 23% (i.e., the CRF is -23), the CMF will be = 1 - (-23/100) = 1.23.
Note: All future reference to countermeasure effectiveness will be expressed as crash modification factor to be consistent with the Highway Safety Manual.
The FHWA Office of Safety offers a variety of resources and training to aid transportation professionals in the application and use of CMFs.