A
Number of crashes
Ai
Area of cross section (average end area method)
Am
Area at midpoint of two cross sections
ai
Layer (course) strength coefficient
AADT
Average annual daily traffic
AASHTO
American Association of State Highway and Transportation Officials
ADT
Average daily traffic
C
Length of Chord
c
Length of subchord
CF
Cubic feet
CRF
Overall crash reduction factor
CRi
Crash reduction factor for a specific countermeasure i