A local agency is installing traffic signals at a stop-controlled intersection to reduce right-angle crashes. The CMF is 0.86. If major-street AADT is 10,000 and minor-street AADT is 8,000, what improvement should be expected?

• A. 0.86% reduction.
• B. A 14% reduction in right-angle crashes.
• C. 86% reduction in all crashes.
• D. A 14% increase in crashes.

Answer: (B)

The key idea is how a Crash Modification Factor (CMF) works. A CMF of 0.86 means the post-treatment crash count is 0.86 times the pre-treatment count for the targeted crash type. That translates to a 1 − 0.86 = 0.14, or a 14% reduction in right-angle crashes.

So, after installing the traffic signal, you should expect about 14% fewer right-angle crashes. If there were 100 such crashes before, roughly 86 would occur after (a reduction of about 14 crashes). The given traffic volumes show the context for CMF applicability, but the improvement percentage comes directly from the CMF value.