What does a CMF represent?

• A. A ratio of the effectiveness of two conditions
• B. A measure of weather severity
• C. A calibration factor for temporal adjustments
• D. A safety program step

Answer: (A)

CMF stands for Crash Modification Factor. The main idea tested is that a CMF is a ratio that shows how crash outcomes change when a safety countermeasure is applied, compared to when it is not. In practice, you’re comparing crashes under two conditions: with the measure in place and without it. This ratio tells you how effective the measure is at reducing (or increasing) crashes. A CMF less than 1 means crashes are reduced (for example, a CMF of 0.8 means a 20% reduction), a CMF of 1 means no change, and a CMF greater than 1 means crashes rise. CMFs are used in planning and evaluating safety improvements to estimate benefits and support cost-benefit analyses. They are not measures of weather severity, not calibration factors for timing, and not steps in a safety program.