CCDL Permit Prep

Doubles / Triples · page 2 of 5

Doubles / Triples questions 21–40

Part of the 100-question Doubles / Triples pool. Each answer cites the FMCSA CDL Manual or the federal rule it comes from.

Practise these as a timed set

  1. What is the FIRST step in uncoupling the rear trailer of a set of doubles?

    • APark the rig in a straight line on firm level groundCorrect
    • BDisconnect the dolly air and electric lines
    • CRelease the converter dolly fifth wheel latch
    • DSlowly pull the tractor, first trailer and dolly forward

    The manual's uncoupling steps start with parking the rig in a straight line on firm level ground, then applying the parking brakes, before any lines or latches are released.

    FMCSA Commercial Driver's License Manual (July 2014) · Section 7.2.2 - Uncoupling Twin Trailers · verified 2026-09-25

  2. When balancing a doubles combination, which trailer is normally placed directly behind the tractor?

    • AThe lighter trailer
    • BThe heavier trailerCorrect
    • CThe longer trailer
    • DThe trailer with the higher center of gravity

    The FMCSA manual's doubles guidance places the heavier trailer closer to the tractor when the set is balanced. Follow the carrier's approved loading procedure and applicable state rules.

    FMCSA CDL Testing System — Doubles/Triples · Doubles and Triples — Trailer Order · verified 2026-09-08

  3. If you brake hard when a combination vehicle is lightly loaded, what can happen?

    • AThe wheels lock up easily and the trailer can swing out and strike other vehiclesCorrect
    • BThe front axle lifts off the road
    • CThe vehicle stops in a shorter distance than when fully loaded
    • DThe vehicle slows evenly with no risk

    A lightly loaded combination has very stiff springs and strong brakes that give poor traction, so wheels lock up easily. The trailer can swing out and the tractor can jackknife.

    FMCSA Commercial Driver's License Manual (July 2014) · Section 6.1.3 - Brake Early · verified 2026-09-25

  4. How should you check that the converter dolly fifth wheel is properly locked after coupling?

    • AUse a controlled coupling pull check, then secure the rig and visually inspect the jaws, plates, and lockCorrect
    • BCheck only the safety chains
    • CPush the dolly by hand and skip the coupling inspection
    • DUse full throttle to test the connection

    Check resistance with a controlled pull and verify the coupling visually. Chains do not show where the fifth-wheel jaws engaged, and high force is not a substitute for either check.

    Oregon DMV Commercial Driver Manual · 7.2 Coupling and Uncoupling; 7.3 Inspection; 7.4 Brake Checks · verified 2026-09-07

  5. During a pre-trip inspection of a converter dolly, what should you confirm about the safety chains?

    • AThey are secured to the trailerCorrect
    • BThey are wrapped around the cargo
    • CThey are coiled loosely on the ground
    • DThey are attached to the tractor's bumper

    The manual's coupling checks state that safety chains should be secured to the trailer(s).

    FMCSA Commercial Driver's License Manual (July 2014) · Section 7.3.1 - Additional Checks (Coupling System Areas) · verified 2026-09-25

  6. Why must you take curves slower in doubles or triples than in a single trailer combination?

    • ATheir engines are always less powerful
    • BA safe curve speed for a single trailer may be too fast for doubles or triples, which are less stableCorrect
    • CFederal law limits all doubles to 55 mph
    • DThey burn more fuel on curves

    The manual says doubles and triples are less stable, and a safe curve speed for a straight truck or single trailer combination may be too fast for doubles or triples.

    FMCSA Commercial Driver's License Manual (July 2014) · Section 7.1.1 - Prevent Trailer from Rolling Over · verified 2026-09-25

  7. When coupling a second trailer, what should you do with the converter dolly air-tank petcock after the dolly is connected?

    • ALeave it open to drain continuously
    • BClose it, then connect the air and electrical lines and charge the trailer brakesCorrect
    • CRemove it before connecting the second trailer
    • DOpen it after charging the trailer brakes

    FMCSA Section 7.2.1 directs the driver to close the converter dolly air-tank petcock after coupling, connect the safety chains, air hoses, and light cords, and then charge and check the trailer brakes. Tank drainage is a separate maintenance check; the coupling procedure does not make a moisture-drain claim.

    FMCSA Commercial Driver's License Manual (2005 CDL Testing System) · Section 7.2.1: Connect Converter Dolly to Rear Trailer · verified 2026-09-08

  8. How do you test the trailer service brakes on a doubles combination?

    • AMove forward slowly and apply the trailer brakes with the hand control (trolley valve), feeling for the brakes to come onCorrect
    • BDrive at highway speed and make a sudden stop
    • CUse only the parking brake and check that the tractor stays still
    • DUse the hand valve for parking overnight

    The manual has you check for normal air pressure, release the parking brakes, move forward slowly and apply the trailer brakes with the hand control; you should feel the brakes come on.

    FMCSA Commercial Driver's License Manual (July 2014) · Section 7.4 / 6.5.2 - Test Trailer Service Brakes · verified 2026-09-25

  9. Why must you turn wide with a long combination vehicle such as doubles?

    • AThe rear wheels follow a different path than the front wheels, and longer vehicles off-track moreCorrect
    • BThe rear trailers always follow exactly in the tractor's path
    • CAir lines shorten in turns
    • DTurning increases engine torque

    The manual explains off-tracking: the rear wheels follow a different path than the front wheels, and longer vehicles off-track more.

    FMCSA Commercial Driver's License Manual (July 2014) · Section 6.1.6 - Turn Wide · verified 2026-09-25

  10. What should you verify about the converter dolly's pintle hook during a doubles pre-trip inspection?

    • AThe pintle eye is in place in the hook and the hook is latchedCorrect
    • BThe hook is unlatched so the dolly can pivot
    • CThe hook is greased and left open
    • DOnly that the dolly is parked straight

    The manual says to be sure the dolly's pintle eye is in place in the pintle hook and that the hook is latched.

    FMCSA Commercial Driver's License Manual (July 2014) · Section 7.3.1 - Additional Checks · verified 2026-09-25

  11. In a set of doubles, where should the most heavily loaded trailer go?

    • AAt the very rear of the set
    • BDirectly behind the tractorCorrect
    • CIt makes no difference to handling
    • DAhead of the converter dolly only

    Weight behind the tractor keeps the combination stable. A heavy trailer at the rear amplifies every steering input and is far more likely to roll.

    FMCSA Commercial Driver License Manual · Section 7: Doubles and Triples · verified 2026-09-08

  12. What is rearward amplification in a set of doubles or triples?

    • AThe trailer brakes apply before the tractor's
    • BThe engine loses power on a grade
    • CThe rear trailer swings harder than the tractorCorrect
    • DFuel use rises as the load shifts back

    A modest steering movement at the tractor becomes a violent sideways swing at the last trailer, which is why sudden lane changes roll these combinations.

    FMCSA Commercial Driver License Manual · Section 7: Doubles and Triples · verified 2026-09-08

  13. The rear trailer is secured and the area is clear. To move a converter dolly into position by hand, what should you do?

    • AWait to inspect the brakes until the trip is over
    • BLeave it free to roll unattended
    • CRemove its brake components
    • DUse the correct brake-release procedure for that dolly and control its movementCorrect

    The positioning procedure releases dolly brakes, using the tank drain on the described non-spring system or the parking control on a spring-brake dolly. Control the dolly and secure it again as required; brake designs differ.

    Oregon DMV Commercial Driver Manual · 7.2 Coupling and Uncoupling; 7.3 Inspection; 7.4 Brake Checks · verified 2026-09-07

  14. How should you check that a converter dolly is properly coupled?

    • AConfirm the pintle hook is latched and chains securedCorrect
    • BLook only at the trailer's landing gear
    • CListen for air escaping at the glad hands
    • DCheck the tire pressure on the dolly axle

    The pintle hook must be closed and locked and the safety chains fastened, because the dolly is the only thing holding the rear trailer to the set.

    FMCSA Commercial Driver License Manual · Section 7: Doubles and Triples · verified 2026-09-08

  15. Why do doubles and triples need more following distance than a single trailer?

    • ATheir brakes are legally weaker
    • BThey take longer to stop and reactCorrect
    • CTheir mirrors show less of the road
    • DTheir engines accelerate more slowly

    More axles, more couplings and more weight mean a longer stop, and any sudden move ripples to the rear trailer instead of being absorbed.

    FMCSA Commercial Driver License Manual · Section 7: Doubles and Triples · verified 2026-09-08

  16. When inspecting a set of doubles, the air lines between trailers must be:

    • ALeft disconnected until the first stop
    • BCoiled tightly against the frame
    • CConnected correctly and clear of snaggingCorrect
    • DWrapped around the safety chains

    Crossed, dragging, or snagged lines can be cut or pulled loose, causing air loss, improper brake response, or emergency-brake application. Connect and route each line correctly before moving.

    FMCSA Commercial Driver License Manual · Section 7: Doubles and Triples · verified 2026-09-08

  17. What is the safest way to steer a set of triples around an obstacle?

    • AAccelerate through the maneuver
    • BSteer sharply and straighten quickly
    • CBrake hard while turning the wheel
    • DSlow first, then steer graduallyCorrect

    Speed plus a quick steering input is what rolls the rear trailer. Reducing speed before the move keeps the amplified swing within the lane.

    FMCSA Commercial Driver License Manual · Section 7: Doubles and Triples · verified 2026-09-08

  18. Before uncoupling a rear trailer, you should first:

    • APark on level ground and secure the trailerCorrect
    • BRelease the dolly brakes fully
    • CRaise the landing gear off the surface
    • DDisconnect the electrical cord only

    Park straight on firm level ground and secure the trailer against movement. Set appropriate brakes or chocks and lower its landing gear before uncoupling. Ground slope, horizontal restraint, and vertical support are separate checks.

    Oregon DMV Commercial Driver Manual · 7.2 Coupling and Uncoupling; 7.3 Inspection; 7.4 Brake Checks · verified 2026-09-07

  19. How does the manual describe the stability of doubles and triples compared with other commercial vehicles?

    • AThey are less stableCorrect
    • BThey are more stable
    • CThey are equally stable
    • DStability is unaffected by trailers

    Section 7.1 says there are more things that can go wrong and doubles and triples are less stable than other commercial vehicles, so take special care.

    FMCSA Commercial Driver's License Manual (July 2014) · 7.1 Pulling Double/Triple Trailers · verified 2026-09-25

  20. When backing a set of doubles, the correct practice is to:

    • ABack with the dolly brakes released
    • BReverse quickly using both mirrors
    • CAvoid it, and get help if unavoidableCorrect
    • DSteer opposite and hold the turn

    A double articulates at two points and is difficult to control in reverse. Avoid backing a set when possible and get help if backing is unavoidable.

    FMCSA Commercial Driver License Manual · Section 7: Doubles and Triples · verified 2026-09-08