Commercial Driver’s License: Endorsement “T”for Double and Triple Trailer Sets

Using a double or triple set of trailers is a great way to get the most efficient use out of your tractor trailer, doing the work of two or three trucks with just one vehicle. Before you pull double or triple sets with your vehicle you will need a “T” endorsement on your commercial driver’s license.

Commercial Driver’s License Restrictions and Endorsements

Here is a full list of the different restrictions and endorsements you can have tacked on to your commercial driver’s. Note that this list is from the DMV website for Minnesota license. Nearly all of these restrictions and endorsement qualification apply nationwide but rules very state by state so be sure to follow the rules set by the DMV in your particular state for operating a double and triple trailer set.

Prerequisites for “T” Endorsement

There are 3 weight classes for commercial driver’s licenses : Class C commercial driver’s licenses permit driving a vehicle under 26,001 pounds, and with this vehicle towing another vehicle under 10,000 pounds. Class B commercial driver licenses permit driving a vehicle over 26,001 pounds, but also have the stipulation of not being able to tow another vehicle over 10,000 pounds. Class A commercial driver licenses allow drivers to operate a vehicle over 26,001 pounds and also tow another vehicle over 10,000 pounds.
Anyone who wishes to pull a double or triple trailer set will first need a Class A commercial driver license. You will also need to pass a knowledge test that proves you possess the skills to drive with two or three trailers without endangering yourself or other drivers. Depending on which state you take this knowledge test in, you may have to pay a testing fee in additional to a fee for having the “T” endorsement applied to their commercial driver’s license.

Where to Take the Knowledge Test

Call your local DMV to make sure they can provide testing for you. Again, requirements and fees for the knowledge vary state by state. Check your local DMV website or call their office to know exactly everything you will need.

How to Pass the Knowledge Test for a “T” Endorsement

There are 4 subjects covered in the knowledge test for pulling double and triple trailers and they are as follows:

  • How to operate a vehicle with double or triple trailers
  • Coupling and uncoupling your trailers
  • Inspecting your double and triple trailers
  • Checking your air brakes

This first section is important because double and triple trailers are very tricky to operate —the additional trailers make your vehicle less stable. A speed that is safe for a regular sized car or even a tractor trailer with only a single trailer may be too fast for a vehicle with multiple trailers. Especially on turns or curves, vehicles with double or triple trailers don’t take much to flip over.
Steering must also be done very carefully and smoothly with no quick jerks. The last trailer at the end of your double or triple set is the one most likely to flip over. When this trailer flips over it will likely bring your other trailers and your cab down along with it—this is known as the “crack the whip” effect.
While driving a vehicle pulling double or triple trailers look ahead to see how traffic is developing further on along the road. When you pull as much weight as a double or triple trailer entails you have very little time to react—be sure to also give the cars in front of you plenty of space in case they brake.
Knowing how to couple and uncouple your multiple trailers is also a key point in keeping yourself and other safe. The damage that results in a trailer detaching while you are driving will cost you a lot of money and could hurt a lot of people.
The heaviest trailer should be connected directly to the cab. The lightest trailer should be in the rear.
Before every trip do a walk around examination of your vehicle with double or triple trailers. Check to see that all of your wheels are secure and all kingpins—check your air powered devices to ensure there are no leaks. Make sure your locking pins are in place. Also make sure that all electrical and air lines are secure and have enough slack to not tear during turns. See that your landing gear is entirely raised and is not damaged. Also check to make sure that the shut off valves at the rear of all front trailers is open and the shut off valve at the rear of the last trailer is closed.
If you review all of this information and research other procedures for operating a vehicle with double or triple trailers you will be sure to pass the knowledge test. Good luck and drive safe.

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