Section 7: Doubles and Triples

Section 7: DOUBLES AND TRIPLES

THIS SECTION COVERS
• Pulling Double/Triple Trailers
• Coupling & Uncoupling
• Inspecting Doubles and Triples
• Checking Air Brakes

This section has information you need to pass the CDL knowledge test for driving safely with double and triple trailers. It tells about how important it is to be very careful when driving with more than one trailer, how to couple and uncouple correctly, and of inspecting doubles and triples carefully. (You should also study Sections 2, 5, and 6.)

7.1 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.

Preventing Trailers 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 double or triple trailers

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 steep gently when pulling trailers. The last trailer in a combination is most likely to turn over. If you don’t understand the crack-the-whip, study sections 6.1 and review figure 6-1 in the Combination Vehicles section.

Inspect Completely
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 slow down or change lanes gradually when necessary.

Manage Space
Doubles and triples take up more space than other commercial vehicles. They are not only longer, but also need more space because they can’t be turned or stopped suddenly. Allow more following distance. Make sure you have large enough gaps before entering or crossing traffic. Before changing lanes, be certain the lane is open, signal, check traffic and avoid sudden turning movements.

Adverse Conditions
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.

Safety First!