http://ops.fhwa.dot.gov/Freight/sw/overview/index.htm federal regulations https://ops.fhwa.dot.gov/Freight/sw/overview/index.htm "Commercial Vehicle Size and Weight Program" 80,000 pounds safe weight limits national weight standards imposes weight restrictions on tractor trailers Federal Highway Administration imposes weight restrictions on tractor trailers http://ops.fhwa.dot.gov/Freight/sw/overview/index.htm Commercial Vehicle Size and Weight Program DOT's website Federal Motor Carrier Safety Administration (FMCSA) reports