You are required to have a USDOT number if you are engaged in interstate commerce using a vehicle with a gross weight rating or gross combination weight of 10,001 pounds or more. Vehicles designed to transport 8 or more passengers (including the driver) for compensation and vehicles designed to transport more than 15 passengers (including the driver) regardless of compensation are also required to have a USDOT number.
Companies hauling hazardous materials requiring placarding across state lines also need a USDOT number, regardless of the vehicle’s weight.