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When uncoupling doubles or triples, what is important to know about unlocking the pintle hook?
When inspecting doubles or triples, in what position should the air shut-off valves be in?
Shut-off valves (at rear of trailers, in service and emergency lines):
When pulling doubles or triples, what is important to know about the order of the trailers?
When inspecting the air brakes on doubles and triples, you wait for air pressure to reach normal, then push in the red “trailer air supply” knob. When you go to the rear of the last trailer, what should you do to complete this check?
When inspecting doubles and triples you must make sure there is air all the way to the back of the last trailer, otherwise what may not work?
Doubles and triples are more likely to turn over than other combination vehicles because of what effect?
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The Doubles and Triples written CDL Exam is required for your doubles and triples endorsement. This section explains how important it is to be careful when driving with more than one trailer, how to couple and uncouple correctly, and about inspecting doubles and triples carefully.
This section covers:
Pulling Double/Triple Trailers
Take special care when pulling two and three trailers. There are more things that can go wrong, and doubles/triples are less stable than other commercial vehicles. Some areas of concern are discussed below.
Prevent Trailer from Rolling Over
To prevent trailers from rolling over, you must steer gently and go slowly around corners, on ramps, off ramps and curves. A safe speed on a curve for a straight truck or a single trailer combination vehicle may be too fast for a set of doubles or triples.
Beware of the Crack-the-Whip Effect
Doubles and triples are more likely to turn over than other combination vehicles because of the "crack-the-whip" effect. You must steer gently when pulling trailers. The last trailer in a combination is most likely to turn over.
There are more critical parts to check when you have two or three trailers. Check them all. Follow the procedures described later in this section.
Look Far Ahead
Doubles and triples must be driven very smoothly to avoid rollover or jackknife. Therefore, look far ahead so you can slow down or change lanes gradually when necessary.
Doubles and triples take up more space than other commercial vehicles. They are not only longer, but also need more space because they cannot be turned or stopped suddenly. Allow more following distance. Make sure you have large enough gaps before entering or crossing traffic. Be certain you are clear at the sides before changing lanes.
Be more careful in adverse conditions. In bad weather, slippery conditions and mountain driving, you must be especially careful if you drive double and triple bottoms. You will have greater length and more dead axles to pull with your drive axles than other drivers. There is more chance for skids and loss of traction.
Parking the Vehicle
Make sure you do not get in a spot you cannot pull straight through. You need to be aware of how parking lots are arranged in order to avoid a long and difficult escape.
Antilock Braking Systems on Converter Dollies
Converter dollies built on or after March 1, 1998, are required to have antilock brakes. These dollies will have a yellow lamp on the left side of the dolly