You must obtain a CDL if you operate:

Any combination of vehicles with a Gross Combination Weight Rating (GCWR) of 26,001 pounds or more, providing the Gross Vehicle Weight Rating (GVWR) of the vehicle being towed is in excess of 10,000 pounds.

Any single vehicle with a GVWR of 26,001 pounds or more, or any such vehicle towing another not in excess of 10,000 pounds.

Any vehicle, regardless of size, designed to transport 16 or more persons, including the driver.

A vehicle required by federal regulations to be placarded while transporting hazardous materials.