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Page 1 Doubles/Triples Test Study Guide for the CDL

General Information

Some drivers will pull double or triple trailers. This study guide gives the basic information necessary to know about pulling doubles/triples.


Double and triple trailers are at a greater risk for rollovers than single trailers, with the last trailer being the most likely to be affected. Sudden movements can make the trailer swing out and then back again, much like the tip of a whip, which is why this swinging is called the “crack-the-whip” effect. You can help prevent trailer rollovers by driving slowly around corners, controlling your speed, and braking early.

Managing Space

Double and triple trailers are longer than single trailers and require more space to be maneuvered. Because of this, more care must be taken to avoid potentially hitting the curb or another vehicle while turning or changing lanes. Slowing down or changing lanes must be done gradually to avoid jackknifing or losing control. Drive carefully in adverse conditions, and always park in a spot you can pull through to help prevent possible accidents.

Special Considerations During Inspections

Consider a few extra things during the standard seven-step inspection of double and triple trailers:

  • The shutoff valves at the rear of the front trailers must be open and the shutoff valves at the rear of the back trailer must be closed.

  • Check if the converter dolly air tank drain valve is also closed.

  • Ensure that air lines are supported and that the glad hands are connected.

  • Check if the spare tire is secured, the pintle-eye of dolly is in place, the pintle hook is latched, the safety chains are secured, and the light cords are firmly in their sockets.

  • Additionally, when loading a double/triple trailer, always ensure the lightest trailer is in the rear and the heaviest is in the front.


Double Trailers

The steps for coupling double trailers are as follows:

1) Secure second trailer
2) Position converter dolly in front of second trailer
3) Couple tractor and first semi-trailer (follow standard procedure)
4) Connect converter dolly to front trailer
5) Connect converter dolly to rear trailer.

To uncouple a double trailer, begin by uncoupling the rear trailer. Uncouple the converter dolly by lowering the landing gear, disconnecting the safety chains, applying the spring brakes or wheel chocks, releasing the pintle hook, and pulling away from the dolly.

Triple Trailers

The steps for coupling triple trailers are as follows:

1) Couple second and third trailers
2) Uncouple tractor and pull away from trailers
3) Couple tractor and first semi-trailer (following standard procedure)
4) Couple tractor and first semi-trailer to second and third trailers.

To uncouple triple trailers, first uncouple the third trailer by pulling out the dolly and unhitching it, using the same method you would for double trailers.