CCDL Permit Prep

Doubles / Triples · page 4 of 5

Doubles / Triples questions 61–80

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 should you check on a glad hand before connecting it?

    • AThe rubber seal is clean and soundCorrect
    • BThe metal is freshly painted
    • CThe coupling turns freely
    • DThe hose is fully coiled

    A cracked or dirty seal leaks air continuously, and the leak shows up as a system that will not hold pressure.

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

  2. Why must the trailer air tanks be charged before moving a set?

    • AThe lights need the air pressure
    • BThe spring brakes stay on without airCorrect
    • CThe dolly cannot turn unpressurised
    • DThe load shifts without pressure

    Spring brakes are held off by air, so an uncharged trailer drags with its brakes locked until the system fills.

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

  3. How do you test the trailer emergency brakes on a set of doubles?

    • ARev the engine in neutral
    • BApply the pedal and listen
    • CPull the air supply and try to moveCorrect
    • DTurn the wheel fully to one side

    Cutting the supply should set the spring brakes, and the set should not move when the tractor tries to pull it.

    FMCSA 2005 CDL Testing System Model Manual (July 2014) · Section 7.4.1 — Doubles/Triples Air Brake Check; Oregon Manual § 7.4.1 cross-check · verified 2026-09-19

  4. How do you test the trailer service brakes on a set?

    • AListen for air at the glad hand
    • BSet the parking brake and rev
    • CCheck the gauge while stationary
    • DMove slowly and apply the trailer brakeCorrect

    The hand valve should produce a firm stop, and if it does not the air is not reaching the trailers behind the tractor.

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

  5. How should a right turn be set up with a set of doubles?

    • ASwing wide only after starting the turnCorrect
    • BSwing wide before beginning the turn
    • CHug the curb through the whole turn
    • DStart from the left lane instead

    Turning wide first opens a gap on the right that a car will fill, and the trailers then close on it as they track inside.

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

  6. What must be verified about the dolly's locking jaws after coupling?

    • AThey are greased and open
    • BThey are closed around the kingpinCorrect
    • CThey are removed for the trip
    • DThey rest above the kingpin

    Verify the jaws engage the kingpin shank, the plates have no gap, and the lock is secured. Apparent contact does not establish proper engagement; a wrong coupling must be corrected before travel.

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

  7. What should the gap between the dolly plate and the trailer apron be?

    • AA hand's width all round
    • BAbout six inches
    • CThere should be no gapCorrect
    • DAs wide as the kingpin

    A visible gap means the trailer is riding on the jaws rather than seated on the plate, and it can drop off.

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

  8. When uncoupling the rear trailer of twin trailers, where should you park the rig?

    • AIn a straight line on firm level groundCorrect
    • BOn a slope so the trailer can roll clear
    • COn a curve for easier dolly release
    • DAnywhere, if the parking brakes are off

    Section 7.2.2 says to park the rig in a straight line on firm level ground and apply the parking brakes so the rig will not move.

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

  9. How should the dolly be aligned before backing under a trailer?

    • ASquarely with the kingpin centeredCorrect
    • BOffset to the driver's side
    • CAngled to ease the approach
    • DTilted forward on its tongue

    An off-center approach lets the kingpin miss the jaws entirely and damage the plate instead of coupling.

    FMCSA 2005 CDL Testing System Model Manual (July 2014) · Section 7.2.1 — Coupling Twin Trailers; Oregon Manual § 7.2.1 cross-check · verified 2026-09-19

  10. How should a converter dolly be secured while parked and uncoupled?

    • ALeft free to roll
    • BChocked or with its brakes setCorrect
    • CTied to the trailer with rope
    • DBalanced on its tongue

    An unsecured dolly rolls on the slightest slope, and it is heavy enough to injure anyone in its path.

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

  11. What should be inspected on the dolly's fifth wheel itself?

    • AFree to slide fore and aft
    • BPainted to match the frame
    • CNo cracks and properly greasedCorrect
    • DWrapped against the weather

    The dolly fifth wheel supports the rear trailer front. Check for damage and required lubrication, plus secure mounting and proper engagement. Cracked or damaged parts require correction before use.

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

  12. What should you check about the second trailer's height before coupling?

    • AResting on the ground
    • BWell above the dolly plate
    • CLevel with the tractor's frame
    • DSlightly lower than the dolly plateCorrect

    Set height so the dolly fifth-wheel plate lifts the trailer slightly as it backs underneath. Too high may prevent correct kingpin engagement; too low can damage the trailer. Verify actual height and coupling afterward.

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

  13. What must be checked about the ABS lamp on trailers and dollies?

    • AIt goes out after the system checksCorrect
    • BIt stays lit while driving
    • CIt flashes at every stop
    • DIt is covered during transit

    Trailers and converter dollies required to have ABS have a yellow malfunction lamp on the left side. As a system check, the lamp comes on at start-up for a bulb check and then goes out quickly (on some older systems it stays on until you exceed about 5 mph). If it stays on after the bulb check, or comes on while driving, that unit may have lost ABS control; you still have normal brakes.

    FMCSA Commercial Driver License Manual · Sections 5.1.16 (Antilock braking systems) and 7.1.8 (Antilock braking systems on converter dollies) · verified 2026-09-29

  14. Why must the lights and reflectors between trailers be checked?

    • AThey power the trailer brakes
    • BOther drivers must see the whole setCorrect
    • CThey warn of a low bridge
    • DThey signal the dolly's position

    Lights and reflectors between trailers help other road users see the full combination and its gaps, especially in low visibility.

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

  15. How does off-tracking change as trailers are added?

    • AOff-tracking disappears entirely
    • BThe rear wheels track wider outside
    • CThe rear wheels cut further insideCorrect
    • DOnly the steer axle is affected

    Each unit follows a tighter path than the one ahead, so the last trailer's wheels cross well inside the tractor's line.

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

  16. How much room does passing another vehicle take with a set of triples?

    • AAbout the same as a car
    • BConsiderably more than a single trailerCorrect
    • CLess because of the extra power
    • DIt depends only on the speed limit

    A triple combination is longer and takes more time and space to pass another vehicle safely than a single trailer.

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

  17. How should a long combination be driven down a steep grade?

    • AIn the highest gear available
    • BIn neutral to save the brakes
    • CIn a low gear chosen before the descentCorrect
    • DWith the trailer brakes alone

    The gear has to be selected at the top because the weight of several trailers makes downshifting mid-grade impossible.

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

  18. What should a driver do about parking space when pulling doubles?

    • AStop on the shoulder instead
    • BPark in any marked car space
    • CReverse into the tightest gap
    • DChoose stops with a pull-throughCorrect

    Backing a long combination is difficult, so choose a pull-through stop when possible instead of relying on a tight reverse maneuver.

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

  19. It is too dark to see the dolly locking jaws clearly. What should you do before accepting the coupling?

    • AImprove lighting and complete the visual inspectionCorrect
    • BAssume the lock is correct because it made a sound
    • CSkip the visual check and drive slowly
    • DUse a harder tug instead of looking

    Do not accept a coupling you cannot inspect. Use adequate light to see the jaws, plates, and lock after securing the vehicle. Sound or a stronger pull does not replace seeing the engagement.

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

  20. What should a pre-trip on a set of doubles include that a single does not?

    • AChecking only the front trailer
    • BWalking the full length between unitsCorrect
    • CSkipping the rear axle group
    • DInspecting the cab twice

    A doubles pre-trip must include the connections and components along the full combination, so the driver must walk the complete set.

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