When is it permissible to tow more than one vehicle on the roadway?

• When the towing vehicle weighs more than 15,000 pounds, has three or more axles, and an air brake system for both vehicles
  Explanation:

  "A person may only operate a motor vehicle on the roadway towing more than one vehicle if the towing vehicle weighs more than 15,000 pounds, has three or more axles, and is equipped with an air brake system for both the towing and towed vehicles."
• When the towing vehicle has two axles and no air brake system
• When the towing vehicle is under 10,000 pounds and has standard brakes
• When both vehicles are of the same size