When combinations of countermeasures are proposed for implementation, the value of the Crash Modification Factor (CMF) for the combination is the product of the CMFs of the individual countermeasures, meaning when CMFs overlap, they are combined multiplicatively. CMFs are considered overlapping when they are applied to the same segment of roadway or intersection, and the selected treatments address the same crash types or severities. If the selected treatments do not address any of the same crash types or severities, the CMFs are not considered overlapping.

The formulas below summarize how the overlapping CMFs and overlapping Annual Crashes Reduced are calculated.

Where:

CMF1 = The first CMF applied

CMF2 = The second CMF applied

CMF3 = The third CMF applied

CMF4 = The fourth CMF applied

Calculation for two overlapping CMFs:

Calculation for three overlapping CMFs:

Calculation for four overlapping CMFs:

To calculate additional overlapping CMFs, follow this pattern up to unlimited overlaps.