23 C.F.R. § 1240 app A to Part 1240
A. In States where State-submitted information on seat belt use rates does not include data for Front outboard occupants in passenger motor vehicles (FOPV), an adjustment will be made based on the national ratio of seat belt use rates for FOPV to the seat belt use rate for the group of occupants and vehicles that were included in the State-submitted information. The national seat belt use rates will be derived from the most recent National Occupant Protection Use Survey (NOPUS). For each affected State, the adjustment will be made by dividing the NOPUS seat belt use rate for FOPV by the NOPUS seat belt use rate for the surveyed group, or the seat belt use rate for the closest available group to the surveyed group. The NOPUS seat belt use rate for FOPV will be derived for each affected State by weighting the NOPUS seat belt use rates for passenger cars and for passenger motor vehicles that are not passenger cars (hereafter LTVs) by the relative number of registrations of passenger cars and LTVs in each State. This method will produce a factor which will be multiplied by the State's survey-based seat belt use rate to produce an adjusted seat belt use rate reflecting the required vehicle and occupant population.
B. The process may be expressed mathematically as follows:
Ua = Us((Npc * Rpc + Nltv * Rltv) / Ns)
Where:
Ua = the adjusted State seat belt use rate
Us = the State-submitted seat belt use rate
Npc = the national front outboard passenger car seat belt use rate from NOPUS
Nltv = the national front outboard LTV seat belt use rate from NOPUS
Rpc = the portion of State passenger motor vehicle registrations that are passenger cars
Rltv = the portion of State passenger motor vehicle registrations that are LTVs
Ns = the national seat belt use rate for the State-surveyed vehicle and occupant population (or closest available group from NOPUS)
23 C.F.R. § 1240 app A to Part 1240