The additive effects method adds the effects of the CMFs together and presumes that the CMFs are independent and do not have overlapping effects. The following is an example of how to calculate the combined CMF value for the additive effects method:

CMF

Combined

= 1 − 1 [(1 −

CMF

1

) + (1 −

CMF

2

) + (1 −

CMF

3

)]

The primary limitation to this approach is the possibility that the combined effects may exceed 100 percent reduction in crashes or a CMF value less than zero.