A person may not operate on a highway which is part of the interstate system any vehicle:

1.    With a single axle that carries a gross weight in excess of twenty thousand pounds [9071.85 kilograms] or a wheel load over ten thousand pounds [4535.92 kilograms]. A wheel may not carry a gross weight over five hundred fifty pounds [249.48 kilograms] for each inch [2.54 centimeters] of tire width except that such limits may not be applied to tires on the steering axle. Steering axle weights are limited to twenty thousand pounds [9071.85 kilograms] or the axle rating established by the manufacturer, whichever is lower. Axles spaced forty inches [101.60 centimeters] apart or less are considered as one axle and, on axles spaced over forty inches [101.60 centimeters] and under eight feet [2.44 meters] apart, the axle load may not exceed seventeen thousand pounds [7711.07 kilograms] per axle. The wheel load, in any instance, may not exceed one-half the allowable axle load. Spacing between axles is measured from axle center to axle center.

2.    Subject to the limitations imposed by subsection 1 on tires, wheel, and axle loads, the gross weight of which exceeds that determined by the formula of:

W = 500 (LN/N-1 + 12N + 36) where W equals maximum weight in pounds carried on any group of more than one axle; L equals distance in feet between the extremes of any group of consecutive axles; and N equals number of axles in the group under consideration, except that two consecutive sets of tandem axles may carry a gross load of thirty-four thousand pounds [15422.14 kilograms] each, providing the overall distance between the first and last axles of the consecutive sets of tandem axles is at least thirty-six feet [10.97 meters]. The gross weight may not exceed eighty thousand pounds [36287.39 kilograms].