The maximum width for commercial motor vehicles is 102.36 inches, with a length of 48 to 53 feet and a height of 13 to 14 feet, according to the US Department of Transportation. The federal government has no legal height limit, but each state determines what height trailers can travel at.
While federal regulations leave it up to states to set length limits, the Department of Transportation claims that states must allow trailers to meet certain baseline specifications. A semi-trailer must be at least 48 feet long. A double trailer must be at least 28 feet long for each trailer. When the cab is included, there is no overall length limit. States can impose restrictions on trailers passing under low overpasses.
The statutory width restrictions do not include specialised devices like rear-view mirrors. Semi-trailers are not allowed to surpass 80,000 pounds on highways in general because too much weight can cause bridges to collapse.
On highways, specialised vehicles are limited in length. The minimum length for traditional auto and boat transfers is 65 feet. Transport trailers for beverages must be 28 feet long. The federal minimum length for saddlemount vehicles is 75 feet. In 1982, linear measurement standards were established, while weight criteria were established in 1991.