The gross weight of vehicles in regular operations (operating without a special permit) is governed by the FBF on Interstate highways, by the State bridge formula on non-Interstate highways, as well as by provisions related to axle spacing and limits on single axle loads.
With respect to those highways not in the Interstate Highway System, in all cases in which it exceeds state law in effect on January 4, 1975, the overall gross weight on the vehicle or combination of vehicles, including all enforcement tolerances, shall be as determined by the following formula:
W = 500((LN ÷ (N–1)) + 12N + 36)
where W = overall gross weight of the vehicle to the nearest 500 pounds; L = distance in feet between the extreme of the external axles; and N = number of axles on the vehicle. However, such overall gross weight of any vehicle or combination of vehicles may not exceed 80,000 pounds including all enforcement tolerances.