Which tool is used to estimate the benefits associated with a particular safety countermeasure?

• A. Benefit-cost ratio
• B. Crash modification factor
• C. Regression-to-mean
• D. Cost per crash avoided

Answer: (B)

The tool used to estimate how many crashes a safety countermeasure will prevent is the crash modification factor. The CMF expresses the ratio of crashes after implementing the measure to the number of crashes that would have occurred without it. This lets you forecast safety benefits by applying the observed effect to current or baseline crash data. For example, if the baseline number of crashes is 100 and the CMF is 0.8, you’d expect about 80 crashes after the countermeasure, meaning roughly 20 crashes are avoided. This direct estimation of the change in crash frequency is why the CMF is the best choice for estimating benefits.

Benefit-cost ratio is a financial metric comparing benefits to costs and doesn’t by itself quantify the crash reduction. Regression-to-mean is a statistical bias that can distort before-after estimates. Cost per crash avoided is a related cost-effectiveness measure that depends on how many crashes are avoided, which you determine from the CMF.