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Section 7: Double/Triple Trailer

7.1 Pulling Double/Triple Trailers

This section has information needed to pass the CDL knowledge exam for driving safely with double and triple trailers. (You also should study Sections 2, 5 and 6.)

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 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 a set of doubles or triples.

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. If you do not understand the crack-the-whip effect, study Section 6.1

Inspect Completely

There are more critical parts to check when you have two or three trailers. Check all of them by following 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.

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 cannot be turned or stopped suddenly. Allow more following distance. Make sure you have large enough gaps before entering or crossing traffic. Be sure you are clear at the sides before changing lanes.

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.

Remember: Suggested speed limits are not designed for trucks, let alone trucks pulling 2 or more trailers.
The "crack-the-whip" effect causes a dangerous situation for the second and third trailer. The last trailer is especially at risk of rolling over due to this effect. Many double/triple trailers experience a rollover of the last trailer only.

CDL:

Commercial Driver's License (CDL)

A CDL is required to drive any of the following vehicles:

  • Any combination of vehicles with a gross combined weight rating (GCWR) of 26,001 or more pounds, providing the gross vehicle weight rating (GVWR) of the vehicle being towed is in excess of 10,000 pounds.
  • Any single vehicle with a GVWR of 26,001 or more pounds, or any such vehicle towing another not in excess of 10,000 pounds.
  • Any vehicle, regardless of size, designed to transport 16 or more persons, including the driver.
  • Any vehicle required by federal regulations to be placarded while transporting hazardous materials.

Combination Vehicle:

A vehicle with two separate parts - the power unit (tractor) and the trailer. Tractor-trailers are considered combination vehicles.

Doubles:

Refers to pulling two trailers at the same time, otherwise known as "pups" or "pup trailers" because they're only about 28 feet long. However there are some states that allow doubles that are each 48 feet in length.

OWI:

Operating While Intoxicated

Review Questions - Click On The Picture To Begin...

Why do you need to manage your space better while pulling doubles/triples?
  • Doubles / triples take up more space in turns
  • Doubles / triples tend to be blown around more during windy conditions
  • All of these answers are correct
  • Doubles / triples require more stopping distance to avoid a jackknife

Quote From The CDL Manual:

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 sure you are clear at the sides before changing lanes.

Next
How can you reduce your chances of a rollover accident when pulling two or three trailers?
  • Be mindful that 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.
  • While taking a tight turn, be sure to brake during the entire turn
  • Always put extra pressure on the service brake so that the rear trailer remains directly behind the first trailer
  • When going around corners, you should make quick movements to swing the rear trailer around directly behind the tractor

Quote From The CDL Manual:

Prevent 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 a set of doubles or triples.

TruckingTruth's Advice:

When it comes to driving doubles or triples, everything you do should be slower and smoother than driving a vehicle with only one trailer.

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Next
Which of the following is true about pulling double or triple trailers?
  • Doubles/triples are less stable than other commercial vehicles
  • Doubles/triples are less prone to rollovers than single trailer vehicles
  • Doubles/triples don't jackknife as easily as single trailer vehicles
  • Doubles/triples are easier to handle in windy conditions than single trailer vehicles

Quote From The CDL Manual:

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.

TruckingTruth's Advice:

Pulling doubles or triples are much more dangerous in nearly every aspect of driving, which is why they require an additional endorsement. Be extra cautious when driving a truck with two or more trailers.

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Finish
Please select an option
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