If two crash countermeasures have CMFs of 0.69 and 0.78 installed together, what is the resultant CMF?

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Study for the Road Safety Professional Level 1 Exam. Enhance your knowledge with multiple-choice questions and explanations. Prepare effectively and succeed!

Multiple Choice

If two crash countermeasures have CMFs of 0.69 and 0.78 installed together, what is the resultant CMF?

Explanation:
When combining crash countermeasures, their CMFs multiply to give the overall CMF. This reflects that each measure reduces crashes by a proportion of what remains after the previous measures, assuming the effects are independent. Compute the product: 0.69 × 0.78 = 0.5382, about 0.54. So the resultant CMF is approximately 0.54, meaning about 46% fewer crashes than the baseline remain after both measures. Why not a sum, average, or maximum? A sum would imply more crashes than the baseline, which isn’t how CMFs work. An average or maximum doesn’t capture the compounded effect of applying both reductions to the same crash counts. The product correctly represents the combined, multiplicative impact on crash numbers.

When combining crash countermeasures, their CMFs multiply to give the overall CMF. This reflects that each measure reduces crashes by a proportion of what remains after the previous measures, assuming the effects are independent.

Compute the product: 0.69 × 0.78 = 0.5382, about 0.54. So the resultant CMF is approximately 0.54, meaning about 46% fewer crashes than the baseline remain after both measures.

Why not a sum, average, or maximum? A sum would imply more crashes than the baseline, which isn’t how CMFs work. An average or maximum doesn’t capture the compounded effect of applying both reductions to the same crash counts. The product correctly represents the combined, multiplicative impact on crash numbers.

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