Tractor trailers or semi trucks, to which they often are referred, can come in a variety of sizes. Federal regulations, however, mandate a specific limit in dimensions on interstates. Federal Rules on Weight The gross maximum weight of a semi truck on federal interstates is 80,000 pounds. Some states allow for temporary permits on this weight limit. Federal Size Rules On federal highways, semi trucks can be up to 102 inches wide and tow one 48-foot trailer or two 28-foot trailers. There is no limit on height in federal law, except for structural clearances. State Variances in Weight On highways that aren’t part of the federal interstate system, some states such as Michigan have restrictions on the amount of weight between two axles that varies according to the season. State Size Variances In Colorado, there is a height limit of 13 feet, except on some designated highways, and total trailer length must be less than 57 feet, 4 inches. Exceptions Many states allow for overweight permits on a temporary basis, as well as oversize loads provided that certain safety conditions are met.
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