An MC number, or Motor Carrier number, is used to identify someone who transports passengers or regulated commodities as part of interstate commerce. The Federal Motor Carrier Safety Administration determines whether an MC number is required for those hired in interstate commerce.
Having an MC number is generally required for individuals who are for-hire carriers, those that transport passengers as part of interstate commerce or those that either transport or arrange for transport of federally regulated commodities. An MC number represents having interstate operating authority. Historically, MC numbers have been used, for example, to search for trucking companies.
By September 2016, a new federal Unified Registration System is expected to streamline the registration process for those involved in providing transportation, and this new system would make MC numbers obsolete. Once the system goes live, carriers would be identified only by USDOT identifiers.