A United States Department of Transportation, or USDOT, number is primarily issued to any business organization that owns commercial vehicles as a means of keeping track of the company's safety rating. The U.S. Federal Motor Carrier Safety Administration, or FMCSA, issues the USDOT number.
FMCSA defines a commercial vehicle as any vehicle that transports either people or goods on state expressways. Vehicles hauling cargo deemed unsafe by the Secretary of Transportation are also mandated to procure a USDOT number.
A USDOT number is used to monitor whether a commercial vehicle owner has complied with the safety regulations imposed by the FMCSA. The agency's official website provides a guideline on how to abide by its safety rules.