If you’re transporting passengers, hauling cargo, transporting hazardous materials in interstate commerce you must have a USDOT number. Also if your truck has a gross vehicle weight ratio of 10,001 pounds or more.
You also need a USDOT number if the vehicle is designed to transport more than 8 passengers for pay or if the vehicle is used to transport more than 15 passengers not for pay such as a school or church event.
This only applies if the vehicle is involved in interstate commerce, such as trade, traffic between two states.
For more information regarding this matter please visit https://www.fmcsa.dot.gov/registration/do-i-need-usdot-number