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Commercial driver’s license (CDL) knowledge tests · California DMV

Pulling Double and Triple Trailers

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Questions and answers

  1. Are triple trailer combinations legal in California?

    No, triple combinations are not legal in California

    Triples are covered in the handbook only because they are legal in many other states.

    Section 7 · SECTION 7: DOUBLES AND TRIPLES ↗

  2. How is the doubles and triples endorsement given?

    By knowledge test only

    The endorsement requires only a knowledge test. Do not bring a set of doubles for a Class A skills test.

    Section 7 · SECTION 7: DOUBLES AND TRIPLES ↗

  3. How stable are doubles and triples compared with other commercial vehicles?

    Less stable

    More things can go wrong with 2 or 3 trailers, and doubles and triples are less stable than other CMVs.

    Section 7 · 7.1 – Pulling Double/Triple ↗

  4. How do you prevent the trailers from rolling over?

    Steer gently and go slowly around corners, on ramps, off ramps, and curves

    Gentle steering and low speed in corners, ramps, and curves prevent rollovers.

    Section 7 · 7.1.1 – Prevent the Trailer From Rolling ↗

  5. A speed on a curve is safe for a straight truck or a single trailer combination. Is it safe for a set of doubles?

    It may be too fast for a set of doubles or triples

    Doubles and triples may need a lower curve speed than a straight truck or single trailer combination.

    Section 7 · 7.1.1 – Prevent the Trailer From Rolling ↗

  6. Why are doubles and triples more likely to turn over than other combination vehicles?

    Because of the “crack-the-whip” effect

    The crack-the-whip effect makes doubles and triples easier to turn over, so you must steer gently.

    Section 7 · 7.1.2 – Beware of the Crack-the-Whip ↗

  7. Which trailer in a combination is most likely to turn over?

    The last trailer

    The last trailer is the one most likely to turn over.

    Section 7 · 7.1.2 – Beware of the Crack-the-Whip ↗

  8. What does having 2 or 3 trailers mean for your inspection?

    There are more critical parts to check, and you must check them all

    More trailers mean more critical parts, and all of them must be checked.

    Section 7 · 7.1.3 – Inspect Completely ↗

  9. Why must you look far ahead when driving doubles and triples?

    So you can slow down or change lanes gradually when necessary

    Doubles and triples must be driven very smoothly to avoid rollover or jackknife.

    Section 7 · 7.1.4 – Look Far Ahead ↗

  10. Why do doubles and triples need more space than other commercial vehicles?

    They are longer and cannot be turned or stopped suddenly

    Besides being longer, they cannot be turned or stopped suddenly, so allow more following distance.

    Section 7 · 7.1.5 – Manage Space ↗

  11. What must you make sure of before entering or crossing traffic with doubles or triples?

    That you have large enough gaps

    Make sure the gaps are large enough, and be certain you are clear at the sides before changing lanes.

    Section 7 · 7.1.5 – Manage Space ↗

  12. Why is there more chance of skids and loss of traction with doubles and triples in adverse conditions?

    You have greater length and more dead axles to pull with your drive axles

    In bad weather, slippery conditions, and mountain driving, be especially careful with double and triple bottoms.

    Section 7 · 7.1.6 – Adverse Conditions ↗

  13. What should you avoid when parking doubles or triples?

    Getting into a spot you cannot pull straight through

    Know how parking lots are arranged so you do not face a long and difficult escape.

    Section 7 · 7.1.7 – Parking the Vehicle ↗

  14. What is a converter gear on a dolly?

    A coupling device of 1 or 2 axles and a fifth-wheel that couples a semitrailer to the rear of a tractor-trailer combination

    The converter dolly turns a tractor-trailer into a double bottom rig.

    Section 7 · 7.2 – Coupling and Uncoupling ↗

  15. Converter dollies built on or after what date are required to have anti-lock brakes?

    March 1, 1998

    Converter dollies built on or after March 1, 1998 must have ABS.

    Section 7 · 7.1.8 – Anti-lock Braking Systems on ↗

  16. How do you know that a converter dolly is equipped with anti-lock brakes?

    It has a yellow lamp on the left side of the dolly

    Dollies with ABS have a yellow lamp on the left side.

    Section 7 · 7.1.8 – Anti-lock Braking Systems on ↗

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