• The rules governing coupling devices and towing methods provide the requirements for vehicle tracking, fifth wheel assemblies, towing of full trailers, and safety devices in case of tow-bar failure or disconnection.
• A tow-bar must be structurally adequate for the weight being drawn, be properly and securely mounted, provide for adequate articulation at the connection without excessive slack, and be provided with a locking device that prevents accidental separation of the towed and towing vehicles.
• The rules applicable to devices used to couple vehicles together to pull trailers do not apply to devices used in driveaway-towaway operations.

The regulations governing the systems used to couple (connect) vehicles together are broken down into two sections: (1) vehicles using standard coupling devices to pull trailers (393.70) and “driveaway-towaway” vehicles, which involves piggy backing and tow-bar towing of other vehicles. (393.71)

Coupling devices and towing methods

The rules governing coupling devices and towing methods provide the requirements for vehicle tracking, fifth wheel assemblies, towing of full trailers, and safety devices in case of tow-bar failure or disconnection.

Tracking — The coupling devices connecting two or more vehicles operated in combination must be designed, constructed, and installed, and the vehicles must be designed and constructed, so that when the combination is operated in a straight line on a level, smooth, paved surface, the path of the towed vehicle will not deviate more than three inches to either side of the path of the vehicle that tows it.

Fifth wheel assemblies — The requirements for the mounting of the lower and upper half of fifth wheel assemblies, the locking of the assembly, and the location of the upper and lower half of the assembly are found in 393.70(b).

Towing full trailers — A full trailer must be equipped with a tow-bar and a means of attaching the tow-bar to the towing and towed vehicles. The tow-bar must:

• Be structurally adequate for the weight being drawn;
• Be properly and securely mounted;
• Provide for adequate articulation at the connection without excessive slack at that location; and
• Be provided with a locking device that prevents accidental separation of the towed and towing vehicles. The mounting of the trailer hitch (pintle hook or equivalent mechanism) on the towing vehicle must include reinforcement or bracing of the frame sufficient to produce strength and rigidity of the frame to prevent its undue distortion.

Safety devices — Every full trailer and every converter dolly used to convert a semitrailer to a full trailer must be coupled to the frame, or an extension of the frame, of the motor vehicle which tows it with one or more safety devices to prevent the towed vehicle from breaking loose in the event the tow-bar fails or becomes disconnected. (393.70(d))

Driveaway-towaway operations

The regulations governing coupling devices and towing methods for driveaway-towaway operations set forth the requirements for the maximum number of vehicles in combination, the carrying of vehicles on a towed or towing vehicle, the prohibition of bumper tow-bars on heavy vehicles, the restraint of the front wheels of a saddle-mounted vehicle, the towing of vehicles in a forward position, and several other important requirements. (393.71)