Federal regulation limit automobile size and weight on commonwealth highways. This contains all interstate highways across the country, as well as other federal roads designated within the nationwide Highway system or nationwide Network.

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Federal weight boundaries of vehicles and axle loading limits are governed by the Federal Bridge law (FBL), which has four primary rules:The best weight permitted on a single axle is 20,000 lbsThe maximum full weight permitted on any 2 consecutive axles spaced eight or fewer feet apart (like tandem axles) is 34,000 lbsThe maximum enabled Gross automobile Weight (GVW), or the maximum enabled total load on any type of group of continuous axles top top a vehicle, is figured out by the Federal bridge Formula (FBF).The best Gross auto Weight (GVW) ~ above Interstate highways is 80,000 lbs, even when the result of the formula is greater.

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The Federal bridge Formula (FBF)

Where:W = the maximum allowed total weight in pounds for all axles in the team (rounded come the nearest 500 lbs, and rounding down when right in the middle - i.e. 62,250 lbs rounds to 62,000, while 62,300 lbs rounds to 62,500)L = the size or street in feet (rounded come the nearest foot) indigenous the facility of the forward-most axle in the team to the center of the rear-most axle in the groupN = the total number of axles in the group

Essentially, the Federal leg Formula allows a vehicle to weigh much more when over there are more axles and/or there is much more distance to spread out its weight out.

The Federal leg Table

For convenience, the federal Highway administration published the Federal leg Table, which enables one to quickly lookup the commonwealth maximum gross weight on a auto or team of continuous axles, based on number of axles and overall axle length: