Examen de práctica de Vehículos combinados

Preguntas de Vehículos combinados con respuestas

Cada pregunta lleva la respuesta, el motivo y la sección del Manual CDL de FMCSA o de 49 CFR de donde proviene. Nada de esto es una pregunta recordada de un examen real.

1. Traducción en revisión. Se muestra el contenido actualizado en inglés. For a conventional fifth wheel, which preparation matches the coupling procedure?

   • ARear edge tilted up and jaws closed
   • BRear edge tilted down and jaws openCorrecta
   • CFifth wheel turned sideways to the kingpin
   • DSliding fifth wheel left unlocked

   Prepare the fifth wheel to receive the kingpin: rear edge down, jaws open, and any slide locked. A closed or misaligned connection can prevent proper engagement.

   Oregon DMV Commercial Driver Manual · 6.2.4 Air-lines; 6.2.5 Hose Couplers; 6.4.1 Coupling; 6.4.2 Uncoupling · verificado 2026-09-07

2. Traducción en revisión. Se muestra el contenido actualizado en inglés. After coupling, when you test the connection by pulling forward, you should:

   • APull gently in low gearCorrecta
   • BRelease the trailer brakes first
   • CNot pull at all—just check visually
   • DPull firmly to ensure the kingpin doesn't pop out

   With the trailer brakes locked and landing gear just clear of the ground, pull gently in low gear. Then secure the tractor and visually inspect the coupling. High force can damage equipment; resistance alone does not show exactly where the jaws engaged.

   Oregon DMV Commercial Driver Manual · 6.2.4 Air-lines; 6.2.5 Hose Couplers; 6.4.1 Coupling; 6.4.2 Uncoupling · verificado 2026-09-07

3. Traducción en revisión. Se muestra el contenido actualizado en inglés. Landing gear is already down. You have uncoupled and stopped with the tractor frame still under the trailer. What comes before pulling fully clear?

   • ADrive away without another check
   • BReconnect the fifth wheel without inspecting
   • CRaise the trailer supports off the ground
   • DSecure the tractor and inspect the landing gear and supporting groundCorrecta

   Keep the frame underneath while you secure the tractor and check that the trailer supports and ground are holding. This pause limits the risk of a drop if the supports sink or fail.

   Oregon DMV Commercial Driver Manual · 6.2.4 Air-lines; 6.2.5 Hose Couplers; 6.4.1 Coupling; 6.4.2 Uncoupling · verificado 2026-09-07

4. Traducción en revisión. Se muestra el contenido actualizado en inglés. Which action provides vertical support for the front of a semitrailer before the tractor is removed during uncoupling?

   • ALower the landing gearCorrecta
   • BRemove the air lines
   • CDisconnect the electrical cord
   • DRelease the parking brake

   Lower the trailer landing gear onto sound supporting ground before releasing the coupling. Air lines, the electrical cord, and a parking brake do not provide vertical support for the trailer nose.

   Oregon DMV Commercial Driver Manual · 6.2.4 Air-lines; 6.2.5 Hose Couplers; 6.4.1 Coupling; 6.4.2 Uncoupling · verificado 2026-09-07

5. Traducción en revisión. Se muestra el contenido actualizado en inglés. What is a 'converter dolly' used for?

   • ATo convert a flatbed to a refrigerated trailer
   • BTo connect a second semitrailer to a lead trailer, forming a double combinationCorrecta
   • CTo connect a full trailer to a tractor
   • DTo convert metric axle weights to U.S. standards

   A converter dolly provides axles and a fifth wheel so another semitrailer can follow the lead trailer. It is a separate coupling unit, not a device for refrigeration, axle measurement, or changing a trailer body.

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

6. Traducción en revisión. Se muestra el contenido actualizado en inglés. When coupling a tractor to a semitrailer, after connecting the air lines you should:

   • ASkip the brake checks if the hoses look connected
   • BMove the trailer immediately to test it
   • CDisconnect the trailer air supply and leave the checks unfinished
   • DSupply air and check trailer brake operation and major air loss before the next coupling stepCorrecta

   Charge to normal pressure and check brake response, crossed lines, and major air loss with the vehicle secured. The mechanical engagement, gentle connection check, and visual inspection come later in this conventional procedure.

   Oregon DMV Commercial Driver Manual · 6.2.4 Air-lines; 6.2.5 Hose Couplers; 6.4.1 Coupling; 6.4.2 Uncoupling · verificado 2026-09-07

7. Traducción en revisión. Se muestra el contenido actualizado en inglés. When trailer air-line couplings use the standard red/blue coding, which pairing is correct?

   • ABlue for service brakes, red for emergency (supply) brakesCorrecta
   • BRed for service, blue for emergency
   • CYellow for service, green for emergency
   • DBoth couplings are the same color

   Red identifies the emergency/supply connection and blue the service connection. Check markings and actual connections; crossed lines can prevent proper brake operation. Do not charge a system with known mismatched lines.

   Oregon DMV Commercial Driver Manual · 6.2.4 Air-lines; 6.2.5 Hose Couplers; 6.4.1 Coupling; 6.4.2 Uncoupling · verificado 2026-09-07

8. Traducción en revisión. Se muestra el contenido actualizado en inglés. During the initial approach, before checking trailer height and backing fully underneath, how should you position the tractor?

   • AAt a high speed to seat the kingpin
   • BWithout aligning the fifth wheel
   • CSlowly, straight back, until the fifth wheel just touches the trailerCorrecta
   • DWhile turning sharply to align with the trailer

   Approach straight and slowly until the fifth wheel just contacts the trailer. Secure the tractor and check height and alignment before the later engagement step. Initial contact alone is not a completed coupling.

   Oregon DMV Commercial Driver Manual · 6.2.4 Air-lines; 6.2.5 Hose Couplers; 6.4.1 Coupling; 6.4.2 Uncoupling · verificado 2026-09-07

9. Traducción en revisión. Se muestra el contenido actualizado en inglés. After coupling, the 'tug test' confirms the connection by:

   • APushing the trailer backward with the tractor at low speed
   • BGently pulling forward with the trailer brakes locked to check it holdsCorrecta
   • CLifting the front of the trailer with a jack
   • DRevving the engine while the trailer brakes are holding

   A gentle pull against locked trailer brakes checks that the connection resists separation. Secure the tractor and also inspect for no plate gap, jaws around the kingpin shank, and a secured locking mechanism. The tug does not replace those visual checks.

   Oregon DMV Commercial Driver Manual · 6.2.4 Air-lines; 6.2.5 Hose Couplers; 6.4.1 Coupling; 6.4.2 Uncoupling · verificado 2026-09-07

10. Traducción en revisión. Se muestra el contenido actualizado en inglés. When uncoupling a loaded semitrailer with conventional landing gear, how far should you lower the supports?

    • AOnly after the tractor is fully clear
    • BLeave the supports off the ground
    • CTo firm ground contact, then a few low-gear turns to relieve some tractor weight without lifting the trailer off the fifth wheelCorrecta
    • DDo not lower them because the trailer is loaded

    For a loaded trailer, firm ground contact plus a few low-gear turns removes some weight from the tractor. Do not jack the trailer off the fifth wheel. An empty trailer needs firm support without the loaded-trailer extra-turn assumption.

    Oregon DMV Commercial Driver Manual · 6.2.4 Air-lines; 6.2.5 Hose Couplers; 6.4.1 Coupling; 6.4.2 Uncoupling · verificado 2026-09-07

11. Traducción en revisión. Se muestra el contenido actualizado en inglés. Before supplying trailer air, you see the blue service hose attached to the red supply connection. What should you do?

    • AKeep the vehicle secured and correct the mismatched connections before chargingCorrecta
    • BSupply air first to see whether the mismatch matters
    • CConnect only one hose and leave the other loose
    • DRelease the trailer brakes and begin backing

    Identify and connect each line to its matching function before supplying air. Then check operation and leakage as prescribed. Do not use an incorrect connection to release brakes or move the trailer.

    Oregon DMV Commercial Driver Manual · 6.2.4 Air-lines; 6.2.5 Hose Couplers; 6.4.1 Coupling; 6.4.2 Uncoupling · verificado 2026-09-07

12. Traducción en revisión. Se muestra el contenido actualizado en inglés. What is the correct order of steps when uncoupling a tractor-semitrailer?

    • ASecure the rig and chock as required → lower trailer landing gear → disconnect lines → unlock → pull partly clear → secure and inspect supports → pull fully clearCorrecta
    • BDisconnect lines → remove the tractor → lower landing gear
    • CChock wheels → remove the tractor → lower landing gear
    • DLower landing gear → remove the tractor without releasing or checking the coupling

    Establish brake/chock restraint and vertical support before separation. Stop with the tractor frame still under the trailer and check the supports before leaving. Chocks are not a final step after the trailer is already unsupported.

    Oregon DMV Commercial Driver Manual · 6.2.4 Air-lines; 6.2.5 Hose Couplers; 6.4.1 Coupling; 6.4.2 Uncoupling · verificado 2026-09-07

13. Traducción en revisión. Se muestra el contenido actualizado en inglés. What does the 'tug test' check when coupling?

    • AThat the air lines are properly connected
    • BThat the fifth wheel jaws are locked around the kingpinCorrecta
    • CThat the landing gear has been raised
    • DThat the trailer tires are properly inflated

    A gentle pull against locked trailer brakes checks that the connection resists separation. Secure the tractor and also inspect for no plate gap, jaws around the kingpin shank, and a secured locking mechanism. The tug does not replace those visual checks.

    Oregon DMV Commercial Driver Manual · 6.2.4 Air-lines; 6.2.5 Hose Couplers; 6.4.1 Coupling; 6.4.2 Uncoupling · verificado 2026-09-07

14. Traducción en revisión. Se muestra el contenido actualizado en inglés. Under 49 CFR 390.5T, which statement describes a full trailer?

    • ANo part of its weight, except the towing device, rests on the self-propelled towing motor vehicleCorrecta
    • BIt is loaded to its gross vehicle weight rating
    • CIt is sealed from weather on all sides
    • DIt has been certified for highway use

    For these federal definitions, a full trailer does not rest on the towing motor vehicle except at the towing device. A semitrailer is constructed so that some part of its weight rests on the towing motor vehicle.

    Electronic Code of Federal Regulations · 49 CFR 390.5T, Trailer definitions · verificado 2026-09-07

15. Traducción en revisión. Se muestra el contenido actualizado en inglés. A combination vehicle cannot complete a right turn without entering another traffic lane. What is the safer turn method?

    • ASwing left before starting the turn and leave the right side open
    • BKeep the rear close enough to block a right-side pass, then turn wide while completing the turnCorrecta
    • CLet the trailer wheels cross the curb if traffic is present
    • DStop diagonally across both lanes before steering

    Off-tracking makes the trailer wheels cut inside the tractor path. Keep the rear close enough to prevent a vehicle from passing on the right, and move wide as you complete the turn. Swinging left before the turn opens a dangerous gap on the right.

    FMCSA Commercial Driver's License Manual · Section 6.1.6: Turn Wide · verificado 2026-09-08

16. Traducción en revisión. Se muestra el contenido actualizado en inglés. What must a driver do before routing a combination vehicle near low bridges or other overhead obstructions?

    • AKnow the actual loaded height and check route clearancesCorrecta
    • BAssume every U.S. highway allows a 13-foot-6-inch vehicle
    • CUse only the posted passenger-car speed limit
    • DRely on the trailer color to determine clearance

    There is no single federal commercial-motor-vehicle height limit. State and route limits vary. Before travel, know the actual loaded height and compare it with posted clearances and the permitted route; do not rely on a common height figure as a national rule.

    FHWA — Federal Size Regulations for Commercial Motor Vehicles · Vehicle height — no federal CMV height requirement; state limits vary · verificado 2026-09-07

17. Traducción en revisión. Se muestra el contenido actualizado en inglés. Under 49 CFR 383.91, which combination is in the Class A CDL category?

    • AA combination with a GCWR of 26,001 pounds or more, towing a unit with GVWR over 10,000 poundsCorrecta
    • BAny vehicle towing a trailer with GVWR over 10,000 pounds, regardless of combination weight
    • CAny vehicle requiring a tanker endorsement
    • DAny school bus towing a trailer

    Under 49 CFR 383.91(a)(1), Class A covers any combination with a gross combination weight rating (GCWR) of 26,001 pounds or more when the towed vehicle or vehicles have a gross vehicle weight rating (GVWR) over 10,000 pounds. Endorsements can add separate requirements.

    eCFR 49 CFR 383.91 — Commercial driver's license classes and endorsements · 383.91(a) — Class A CDL · verificado 2026-09-23

18. Traducción en revisión. Se muestra el contenido actualizado en inglés. What connects a tractor to a semi-trailer?

    • AThe pintle hook and eye
    • BThe fifth wheel and kingpinCorrecta
    • CThe converter dolly tongue
    • DThe landing gear brace

    The trailer kingpin engages the tractor fifth wheel. The connection supports the trailer front and transmits forces between units; the trailer axles support the rear. Check the coupling before travel.

    Oregon DMV Commercial Driver Manual · 6.2.4 Air-lines; 6.2.5 Hose Couplers; 6.4.1 Coupling; 6.4.2 Uncoupling · verificado 2026-09-07

19. Traducción en revisión. Se muestra el contenido actualizado en inglés. What is the purpose of the tractor protection valve in a combination vehicle?

    • ARaises the trailer's landing gear
    • BApplies the trailer brakes at every stop
    • CKeeps air in the tractor if the trailer breaks awayCorrecta
    • DLocks the fifth wheel in position

    The tractor protection valve keeps air in the tractor or truck brake system if the trailer breaks away or develops a bad leak. When it closes, it stops air from leaving the tractor and vents the trailer emergency line, which applies the trailer emergency brakes.

    FMCSA Commercial Driver License Manual · Section 6.2.2: Tractor Protection Valve · verificado 2026-09-08

20. Traducción en revisión. Se muestra el contenido actualizado en inglés. According to the FMCSA model CDL manual, what can happen if the service and emergency air lines are crossed?

    • AYou could drive away without trailer brakesCorrecta
    • BThe trailer brakes will drag continuously
    • CThe tractor will lose its parking brake
    • DThe trailer lights will stop working

    The FMCSA model manual says crossed lines can send supply air to the service line instead of charging trailer tanks. On older trailers, you could drive away without trailer brakes. Test trailer brakes before driving.

    FMCSA Model Commercial Driver License Manual · Section 6.2: Air-line connections and trailer brakes · verificado 2026-09-07