What does the Crash Modification Factors (CMFs) indicate?

The Crash Modification Factors (CMFs) are used primarily to estimate the effect of a specific roadway feature or traffic control device on the frequency of crashes. They indicate the effectiveness of a particular safety measure compared to a baseline condition. Consequently, the CMF reflects the ratio of crashes expected after a safety intervention to the number that would be expected without the intervention. A CMF greater than 1 indicates an increase in crashes, while a CMF less than 1 suggests a reduction in crashes.

The other choices, while related to crash data analysis, do not accurately describe CMFs. The statistical model used to adjust expected crash frequency refers to methodologies that might incorporate CMFs but does not define what they are. Estimation of crash severity focuses on the impacts of crashes rather than the frequency, which is not the purpose of CMFs. Finally, the distribution of crash counts pertains to how crashes are spread across different types of facilities or locations, which is distinct from the function of CMFs. The correct characterization of CMFs as an effectiveness ratio captures their role in evaluating the impact of safety interventions.