CCDL Permit Prep

Doubles / Triples · page 3 of 5

Doubles / Triples questions 41–60

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. The tractor and first semitrailer are already coupled. Before positioning the dolly for the rear trailer, what is essential?

    • ASecure the rear trailer against movementCorrect
    • BUnlock the first trailer fifth wheel
    • CLeave both trailers free to roll
    • DDisconnect every brake before checking the area

    The rear trailer must not roll when the dolly approaches. Use the applicable brakes and chocks before positioning and coupling. Follow the sequence for the equipment in use.

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

  2. Before coupling a rear trailer to a converter dolly, you should first:

    • ADrain it completely and leave it
    • BMake sure the trailer brakes are locked and/or the wheels are chockedCorrect
    • CFill it with the trailer service line
    • DDisconnect it from the system

    Before backing the converter dolly under the rear trailer, make sure the trailer brakes are locked or the wheels are chocked so the trailer cannot move.

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

  3. Why is a triple harder to control than a double?

    • AIts tractor has less power available
    • BIts brakes are legally weaker
    • CEach added trailer amplifies the swing moreCorrect
    • DIts mirrors cover a smaller area

    Rearward amplification compounds with each trailer, so the last one in a triple swings far harder than the last in a double for the same steering input.

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

  4. What should you inspect on the pintle hook of a converter dolly?

    • AWrapped in protective tape
    • BFreshly greased and repainted
    • CFree to swing loosely
    • DLatched, locked and not worn or crackedCorrect

    The pintle hook is the single point holding the rear trailer to the set, so a worn or unlatched hook is how a trailer separates on the road.

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

  5. What should you do about the safety chains on a converter dolly?

    • ASecure them to the trailer frame with enough slack for turns and keep them from draggingCorrect
    • BPull them tight to the frame with no slack so the dolly cannot sway
    • CRemove them once the pintle hook is locked, since they are only for towing
    • DLoop them over the air lines so the lines are supported in turns

    Safety chains are a backup if the hook fails. Secure them to the trailer frame, allow enough slack for turns, and keep them from dragging.

    FMCSA Commercial Driver License Manual · Section 7: Doubles and Triples · verified 2026-09-29

  6. Why must you be especially careful driving doubles or triples in bad weather or on slippery roads?

    • AThere is more chance for skids and loss of tractionCorrect
    • BThey stop shorter on slippery roads
    • CThey grip better than a single trailer
    • DSteering becomes lighter and safer

    Section 7.1.6 says the greater length and more dead axles pulled by the drive axles mean more chance for skids and loss of traction.

    FMCSA Commercial Driver's License Manual (July 2014) · 7.1.6 Adverse Conditions · verified 2026-09-25

  7. What should you do before backing under a second trailer?

    • ARaise its landing gear first
    • BRelease its brakes fully
    • CChock or brake it so it cannot moveCorrect
    • DOpen its rear doors

    A trailer free to roll moves as the dolly touches it, so it is held still before anything is reversed underneath.

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

  8. Why should landing gear be raised all the way before driving?

    • APart way up it may catch on railroad tracks or other thingsCorrect
    • BIt changes the fifth wheel position
    • CIt alters trailer brake timing
    • DIt affects fuel economy

    The manual says never drive with the landing gear only part way up because it may catch on railroad tracks or other things.

    FMCSA Commercial Driver's License Manual (July 2014) · Section 6 Uncoupling, Step 4 (raise landing gear) · verified 2026-09-25

  9. When a trailer's wheels lock up, in which condition is the trailer most likely to swing around?

    • AEmpty or lightly loadedCorrect
    • BFully loaded
    • CLoaded with cargo low to the ground
    • DOnly when parked

    Section 6.1.5 says a trailer whose wheels lock will tend to swing around, and this is more likely when it is empty or lightly loaded.

    FMCSA Commercial Driver's License Manual (July 2014) · 6.1.5 Prevent Trailer Skids · verified 2026-09-25

  10. With the rig secured and trailer supply charged to normal pressure, which check shows supply air reaches the last trailer?

    • AOpen the drain valve on the first trailer's air tank and listen for air
    • BPull the trailer air supply knob out and watch the last trailer's lights
    • CBriefly open the emergency-line shut-off at the rear of the last trailer, listen for air, then close itCorrect
    • DApply the trailer hand valve, then check that the tractor brakes alone hold the whole combination in place on a grade

    Escaping air at the last trailer confirms the supply path reaches that point. Close the valve after checking. The service-line path needs its separate prescribed check; this is not a complete brake inspection.

    Oregon DMV Commercial Driver Manual · 7.2 Coupling and Uncoupling; 7.3 Inspection; 7.4 Brake Checks · verified 2026-09-29

  11. What should you do if the rear trailer of a set begins to swing?

    • ASteer sharply the other way
    • BBrake hard immediately
    • CRelease the brakes and steer smoothly; do not use the trailer hand valveCorrect
    • DAccelerate to pull it into line

    For a trailer skid or swing, release the brakes to restore traction and keep steering smooth. Do not use the trailer hand valve to straighten the rig.

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

  12. Why does a set of doubles need a longer gap to cross traffic?

    • AIts mirrors block the side view
    • BIts engine cannot accelerate at all
    • CIts brakes take longer to release
    • DIts extra length clears the road slowlyCorrect

    The whole combination has to clear before traffic arrives, and the last trailer is still in the intersection well after the tractor has left it.

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

  13. What should you inspect where the dolly tongue meets the front trailer?

    • ASecure connection with no cracksCorrect
    • BThat it is freshly painted
    • CThat it moves loosely up and down
    • DThat the wiring is disconnected

    That joint carries the pull of everything behind it, so a crack or loose fastening there is a separation waiting to happen.

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

  14. When parking doubles or triples, what should you avoid?

    • AA spot you cannot pull straight throughCorrect
    • BA spot you can pull straight through
    • CAny lot with wide lanes
    • DAny lot with a paved surface

    Section 7.1.7 says not to get in a spot you cannot pull straight through, so you avoid a long and difficult escape.

    FMCSA Commercial Driver's License Manual (July 2014) · 7.1.7 Parking the Vehicle · verified 2026-09-25

  15. Traffic beyond a rail crossing leaves room for the tractor and first trailer but not the rear trailer. What should the doubles driver do?

    • AEnter because the tractor will clear
    • BEnter slowly and stop with the last trailer on the tracks
    • CWait before the crossing until the entire combination can clearCorrect
    • DUncouple a trailer on the tracks

    The available space must hold the entire set clear of the rails. Entering with only part of the combination able to clear risks trapping the rear trailer in a train path.

    Oregon DMV Commercial Driver Manual · 7.1 Pulling Double/Triple Trailers · verified 2026-09-07

  16. What is the rule for the shut-off valves at the rear of the last trailer?

    • AThey must be left cracked
    • BThey must be fully open
    • CThey must be removed
    • DThey must be closedCorrect

    The last trailer has nothing behind it, so both rear shut-off valves must be closed. An open service valve prevents proper service-brake pressure, while an open emergency valve can drain supply air and apply the trailer spring brakes.

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

  17. What is the rule for shut-off valves on trailers ahead of the last one?

    • AThey must be openCorrect
    • BThey must be closed
    • CThey must be capped off
    • DThey must be drained

    Air has to pass through each trailer to reach the ones behind it, so every valve except the last set stays open.

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

  18. What happens if the last trailer's shut-off valves are left open?

    • AThe trailer lights stop working
    • BThe rear trailer may lose brake pressureCorrect
    • CThe dolly will not steer
    • DThe tractor loses power

    An open last-trailer valve vents the air line. The rear trailer may lose the pressure needed for its brakes to apply.

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

  19. What do the blue and red glad hands carry?

    • ABrake fluid and coolant
    • BElectrical power and ground
    • CService air and emergency airCorrect
    • DFuel and exhaust

    Blue feeds the service line the brake pedal controls; red feeds the emergency line that holds the spring brakes off.

    FMCSA 2005 CDL Testing System Model Manual (July 2014) · Section 6.2.5 — Glad Hands; Oregon Manual §§ 6.2.4–6.2.5 cross-check · verified 2026-09-19

  20. What happens if the service and emergency glad hands are cross-connected?

    • AThe engine will not start
    • BThe trailer lights reverse polarity
    • CThe dolly locks in position
    • DThe trailer brakes may not work correctlyCorrect

    Cross-connected lines send supply air to the service line instead of charging the trailer air tanks. The trailer’s spring brakes may not release. On older trailers without spring brakes, loss of tank air can leave no emergency braking. Test that the trailer brakes work before moving.

    FMCSA 2005 CDL Testing System Model Manual (July 2014) · Section 6.2.5 — Glad Hands; Oregon Manual §§ 6.2.4–6.2.5 cross-check · verified 2026-09-19