A USDOT number is a unique identifier given to certain types of commercial businesses by the Federal Motor Carrier Safety Administration (FMCSA) to help monitor and streamline safety compliance. It is required for companies that operate commercial vehicles transporting passengers or hauling cargo in interstate commerce. Commercial intrastate hazardous materials carriers who haul types and quantities requiring a safety permit must also register for a USDOT number. The number serves as a unique identifier when collecting and monitoring a companys safety information acquired during audits, compliance reviews, crash investigations, and inspections. Companies can determine if they need a USDOT number by visiting the FMCSAs website and completing an interactive quiz that asks a series of questions about their vehicles and business. Some states also require intrastate commercial motor vehicle registrants to obtain a USDOT number.