A CMF of 0.86 is applied to reduce crashes at a signalized intersection. With an approach AADT of 10,000 and a minor street AADT of 8,000, what percentage reduction in right-angle crashes would you expect?

• A. No change in crashes
• B. 86% reduction
• C. 14% reduction
• D. 28% reduction

Answer: (C)

A CMF shows how crashes change after a safety measure is put in place. A CMF of 0.86 means you should expect 0.86 times as many crashes as before, or 14% fewer crashes (since 1.00 − 0.86 = 0.14). The traffic volumes on the two approaches tell you about exposure but don’t alter the percentage change implied by the CMF. So the expected reduction in right-angle crashes is 14%. The other options don’t fit because a CMF of 0.86 does not mean an 86% reduction, no change, or a 28% reduction (those would correspond to different CMF values).