Test de práctica CDL Combination Vehicles

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Las 15 preguntas de un vistazo

¿Prefieres leer antes de jugar? Abajo están todas las preguntas de la muestra. Las respuestas y explicaciones quedan plegadas hasta que las abras.

1. 1. Which pair of habits does the most to keep a loaded combination vehicle from rolling over?

   • A. Load the heaviest cargo on top and brake hard just before each curve
   • B. Push the load toward one side wall so it cannot shift, and keep your speed up through ramps
   • C. Keep the cargo as close to the ground as possible, and drive slowly around turns
   • D. Run the trailer a little overloaded so it settles lower on its springs
   Ver respuesta y explicación

   Respuesta: C. Keep the cargo as close to the ground as possible, and drive slowly around turns

   Stacking cargo high raises the center of gravity, and a higher center of gravity tips more easily, which is why a fully loaded rig is far more likely to roll in a crash than an empty one. Keeping the load low and slowing down for corners, ramps and off ramps are the two things a driver controls directly. Centering the load matters too, because a load pushed to one side makes the trailer lean and starts the roll for you.

2. 2. You are making a tight right turn and cannot finish it without using part of the next lane. What does off-tracking tell you to do?

   • A. Swing wide to the left before you start the turn, so the trailer has room
   • B. Start the turn close to the curb and swing wide as you complete it, keeping the rear near the curb
   • C. Turn from the left lane every time, because the trailer wheels track outside the tractor wheels
   • D. Nothing, since off-tracking only affects backing
   Ver respuesta y explicación

   Respuesta: B. Start the turn close to the curb and swing wide as you complete it, keeping the rear near the curb

   Going around a corner, the rear wheels follow a tighter path than the front wheels, and the rear wheels of the trailer cut in the most. So you have to steer the front end wide enough that the rear does not climb the curb. Swinging left first invites a following driver to think you are turning left and slip up your right side, which is where your trailer is about to be. Turning wide at the end instead, with the rear kept close to the curb, blocks that gap.

3. 3. Rearward amplification, the crack the whip effect, is greatest in which of these?

   • A. A bobtail tractor with no trailer
   • B. A three axle tractor pulling one short semitrailer
   • C. A five axle tractor semitrailer with a 45 foot trailer
   • D. The last trailer of a set of triples
   Ver respuesta y explicación

   Respuesta: D. The last trailer of a set of triples

   In a quick lane change, each trailer swings harder than the unit ahead of it, so the more trailers you add, the more the back one whips. The CDL manual charts this: a five axle tractor semitrailer sits near the bottom of the scale and triples sit at the top, roughly three and a half times as easy to roll at the last trailer. That is why you steer gently and smoothly, look far enough ahead to avoid sudden lane changes, and slow down before a turn rather than during it.

4. 4. You brake hard on a wet ramp and see in your mirror that the trailer is starting to swing out. What is the first thing you do?

   • A. Release the brakes so the trailer wheels can roll and get traction back
   • B. Press the brake pedal harder to pull the trailer back in line
   • C. Apply the trailer hand valve to straighten the rig out
   • D. Set the parking brake and steer toward the shoulder
   Ver respuesta y explicación

   Respuesta: A. Release the brakes so the trailer wheels can roll and get traction back

   A trailer jackknife starts when the trailer wheels lock up and slide, which happens most easily when the trailer is empty or lightly loaded. Locked wheels cannot steer or track, so the fix is to stop braking and let them roll again. Once they grip, the trailer follows the tractor and straightens itself out. Checking your mirrors every time you brake hard is what buys you the time to catch it, because once the trailer leaves your lane it is very hard to save.

5. 5. What is the trailer hand valve, also called the trolley valve or Johnson bar, actually for?

   • A. Holding the rig on a grade instead of using the parking brakes
   • B. Straightening the rig out when the trailer begins to swing
   • C. Testing the trailer brakes, and nothing else
   • D. Releasing the trailer spring brakes before you pull away
   Ver respuesta y explicación

   Respuesta: C. Testing the trailer brakes, and nothing else

   The hand valve applies the trailer brakes only, which is exactly the condition that starts a trailer skid, so it has no place in normal driving. The foot brake sends air to every brake on the rig, tractor and trailer together, and is far less likely to jackknife you. It is also wrong for parking, because on a trailer without spring brakes the air can leak away overnight and release the brakes, so use the parking brakes and chock the wheels.

6. 6. You crawl under with a flashlight after coupling and see a gap between the upper and lower fifth wheel. What does that mean?

   • A. The coupling is wrong, and the kingpin may be sitting on top of the closed jaws
   • B. It is normal, because the plate needs clearance for grease
   • C. The trailer is loaded too heavy and is lifting the plate slightly
   • D. Nothing, as long as the tug test already passed
   Ver respuesta y explicación

   Respuesta: A. The coupling is wrong, and the kingpin may be sitting on top of the closed jaws

   There should be no visible space at all between the upper and lower fifth wheel. A gap usually means the jaws closed before the kingpin dropped in, so the pin is resting on top of them instead of being captured, and the trailer can come loose very easily. This is one of the reasons you shut the engine off, take the key with you and look with a light rather than trusting the tug test alone. If the coupling is not right, do not drive it, get it fixed.

7. 7. When you look into the back of the fifth wheel, the locking jaws should be closed around which part of the kingpin?

   • A. The head
   • B. The shank
   • C. The base plate
   • D. The trailer apron
   Ver respuesta y explicación

   Respuesta: B. The shank

   The kingpin has a base, a narrower shank and a wider head at the bottom. The jaws are meant to wrap the shank, so the head sits below them and cannot pull up through. Jaws closed around the head look locked from a distance but hold almost nothing. While you are under there, also confirm the locking lever is in the lock position and the safety latch is seated over it, since on some fifth wheels that catch has to be placed by hand.

8. 8. You couple to a modern trailer with spring brakes and accidentally cross the air lines. What happens?

   • A. The trailer brakes drag but the rig still rolls normally
   • B. Nothing changes, because both lines carry the same air
   • C. The marker lights fail while the brakes keep working
   • D. Supply air goes to the service line, the trailer tanks never charge, and the spring brakes will not release
   Ver respuesta y explicación

   Respuesta: D. Supply air goes to the service line, the trailer tanks never charge, and the spring brakes will not release

   Air meant to fill the trailer tanks gets sent down the service line instead, so there is never enough pressure to push the spring brakes off. If you push the trailer air supply control and the spring brakes stay set, check your glad hand connections first. The dangerous version is an older trailer with no spring brakes and a drained tank: crossed lines there let you drive away with no trailer brakes at all, which is why you shut the engine off and listen for the trailer brakes applying and releasing before you move.

9. 9. A trailer breaks away and tears the emergency line apart. What happens next?

   • A. The tractor loses its air too, and the driver is left with no brakes
   • B. The tractor protection valve closes to keep air in the tractor, and the trailer emergency brakes come on
   • C. Only the trailer lights go out, because the emergency line is electrical
   • D. The service line keeps the trailer brakes released until the trailer tank drains
   Ver respuesta y explicación

   Respuesta: B. The tractor protection valve closes to keep air in the tractor, and the trailer emergency brakes come on

   The emergency line does two jobs: it charges the trailer air tanks and it holds the trailer emergency brakes off. Lose pressure in it and those brakes apply on their own. At the tractor end, the tractor protection valve shuts so the tractor keeps the air it needs for its own brakes, and the red eight sided trailer air supply knob pops out. That valve closes by itself once pressure falls into the range the manufacturer specifies, usually somewhere between 20 and 45 psi.

10. 10. Before you back the tractor under the trailer, which of these must already be done?

    Marca todas las que correspondan.

    • A. The trailer wheels are chocked, or the trailer spring brakes are set
    • B. The tractor is lined up directly in front of the trailer, not at an angle
    • C. The trailer is set low enough that the tractor lifts it slightly as it backs under
    • D. The landing gear is fully raised and the crank handle is secured
    • E. The electrical cord is plugged into the trailer and the safety catch is fastened
    Ver respuesta y explicación

    Respuesta: A. The trailer wheels are chocked, or the trailer spring brakes are set, B. The tractor is lined up directly in front of the trailer, not at an angle, C. The trailer is set low enough that the tractor lifts it slightly as it backs under

    Chocking or setting the trailer brakes keeps the trailer from walking away as the tractor pushes into it. Backing under at an angle can shove the trailer sideways and snap the landing gear, so line up straight and check both sides in your mirrors. Trailer height matters in both directions: too low and you hit the trailer nose, too high and the pin will not seat. The electrical cord goes on after you have crawled under and inspected the coupling, and the landing gear comes up last of all.

11. 11. Which walkaround checks are added because the vehicle is a combination, and are not part of a straight truck inspection?

    Marca todas las que correspondan.

    • A. The lower fifth wheel is mounted securely, greased, with no visible space against the upper plate
    • B. The air and electrical lines are connected, undamaged, and secured with enough slack for turns
    • C. The landing gear is fully raised and undamaged, with the crank handle in place and secured
    • D. The windshield wipers are secure and the blades are not torn
    • E. The steering wheel has no more than the allowed amount of free play
    Ver respuesta y explicación

    Respuesta: A. The lower fifth wheel is mounted securely, greased, with no visible space against the upper plate, B. The air and electrical lines are connected, undamaged, and secured with enough slack for turns, C. The landing gear is fully raised and undamaged, with the crank handle in place and secured

    You still run the same seven step inspection, plus a set of items that only exist once there is a trailer behind you: the coupling system, the lines that cross to the trailer, and the landing gear. On a sliding fifth wheel you also confirm every locking pin is present and locked, and that the fifth wheel is not so far forward that the tractor frame will strike the landing gear in a sharp turn. Wipers and steering play belong to the ordinary inspection you already do on any vehicle.

12. 12. You are dropping a loaded trailer. Which of these are the correct actions?

    Marca todas las que correspondan.

    • A. Shut off the trailer air supply to lock the trailer brakes, back up gently against the kingpin, then set the parking brake while the tractor is still pushing
    • B. After the landing gear makes firm contact with the ground, crank a few extra turns in low gear to take some weight off the fifth wheel
    • C. Pull forward only until the fifth wheel clears, leaving the tractor frame under the trailer, then get out and check the supports
    • D. Pull the release handle and drive straight out in one move, since the landing gear will catch the trailer
    • E. Leave the air lines connected so the trailer keeps its brakes applied after you drive away
    Ver respuesta y explicación

    Respuesta: A. Shut off the trailer air supply to lock the trailer brakes, back up gently against the kingpin, then set the parking brake while the tractor is still pushing, B. After the landing gear makes firm contact with the ground, crank a few extra turns in low gear to take some weight off the fifth wheel, C. Pull forward only until the fifth wheel clears, leaving the tractor frame under the trailer, then get out and check the supports

    Backing gently against the kingpin takes the load off the locking jaws so the release handle will move, and setting the parking brake holds it there. On a loaded trailer, a few extra cranks lift a little weight off the fifth wheel, which makes the jaws easier to open now and easier to couple next time, though you never lift the trailer off the plate. Stopping with the tractor frame still under the trailer means that if the landing gear sinks or collapses, the trailer lands on your frame instead of the ground.

13. 13. Complete the sentence.

    On a rig pulling more than one trailer, the shut-off valves in the service and supply lines must be _____ at the rear of the last trailer and _____ on all the others.

    Opciones para el hueco 1: open, closed, removed

    Opciones para el hueco 2: open, closed, capped

    Ver respuesta y explicación

    Respuesta: closed, open

    Those valves exist so the lines can be sealed off when nothing is being towed behind that trailer. Leave the last one open and air escapes out the back, so nothing downstream of the leak builds pressure. Leave a middle one closed and the trailers behind it never get air at all. You check this by opening the valve at the rear of the last trailer and listening for air, which proves the whole system is charged all the way back.

14. 14. Complete the sentence.

    To check that the coupling caught, raise the landing gear slightly off the ground, keep the trailer brakes locked, and _____.

    Opciones para el hueco 1: pull the tractor gently forward, rock the tractor back and forth in reverse, release the parking brake and let the rig roll backward, apply full throttle against the trailer

    Ver respuesta y explicación

    Respuesta: pull the tractor gently forward

    A gentle tug against locked trailer brakes is the quickest proof that the jaws actually captured the kingpin rather than sliding past it. Keep it gentle, because a hard pull against a bad coupling is how a trailer ends up on the ground. Passing the tug is not the end of it either. You still put the transmission in neutral, set the parking brakes, shut the engine off, take the key with you and inspect the coupling by eye before anything else.

15. 15. Complete the sentence.

    The service line, which carries the air your foot brake meters out to the trailer, is usually color coded _____, while the emergency line, which fills the trailer air tanks and holds the emergency brakes off, is usually color coded _____.

    Opciones para el hueco 1: blue, red, green, yellow

    Opciones para el hueco 2: blue, red, black

    Ver respuesta y explicación

    Respuesta: blue, red

    The service line is also called the control line or signal line, and the pressure in it rises and falls with how hard you press the pedal, which is what tells the relay valves how much brake to apply. The emergency line is also called the supply line, and it does the two jobs above at once. Colors are a helpful habit and not a guarantee, so read the metal tags stamped service and emergency when they are fitted, and clean the rubber seals before you couple the glad hands.

Qué entra de verdad en el test de combination vehicles

El test de combination vehicles es uno de los tests teóricos que haces en la oficina de licencias de tu estado, y lo hace todo solicitante de Class A. Es aparte del test de general knowledge, aparte del de air brakes y aparte del endorsement de doubles and triples, así que la mayoría de solicitantes de Class A acaban haciendo al menos tres tests escritos antes de tocar un camión. Cada estado escribe sus propias preguntas a partir del mismo modelo de manual del CDL, así que el número de preguntas, el límite de tiempo, la tasa y cuánto tardas en poder repetir tras un suspenso varían según el estado. La nota de corte no varía igual. Las normas federales exigen acertar al menos el 80 por ciento de las preguntas en cada test teórico, así que un estado que te dé 20 preguntas te deja fallar cuatro, y uno que te dé 50 te deja fallar diez.

El contenido sale de la Section 6 del manual del CDL de tu estado y se divide en cinco partes. Conducir vehículos combinados con seguridad cubre el riesgo de vuelco y el centro de gravedad, girar el volante con suavidad y el efecto látigo, frenar pronto, los remolques bajos que se quedan encallados en pasos a nivel elevados, los derrapes de remolque, abrir el giro por el off-tracking (que las ruedas traseras describen una curva más cerrada que las delanteras) y dar marcha atrás con remolque. Los frenos de aire de vehículos combinados cubren la válvula de mano del remolque, la tractor protection valve, el mando de suministro de aire al remolque, las líneas de servicio y de emergencia, las glad hands (los acoplamientos rápidos de las mangueras), los depósitos de aire del remolque y las llaves de corte. Los frenos antibloqueo tienen una parte corta propia, casi toda sobre lo que el ABS no hace por ti. Después vienen los pasos numerados de acople y desacople y los puntos extra que se añaden a la vuelta de inspección en cuanto llevas un remolque detrás.

Los pasos de acople y desacople merecen la mayor parte de tu tiempo de estudio, porque aparecen dos veces. Se preguntan en este test escrito y, más adelante, tienes que encontrar, tocar y nombrar en voz alta las piezas del acople durante la parte de inspección previa del examen práctico. Hay otras dos cosas que conviene resolver pronto. Descarga el manual de tu propio estado en vez de un PDF genérico, porque tu estado escribe sus preguntas a partir de la versión que publica y la redacción coincidirá. Y comprueba cómo estás con el entry level driver training. Desde febrero de 2022, las normas federales exigen formación con un proveedor del registro federal antes de poder hacer el examen práctico de una primera licencia Class A, y ese es un paso aparte de cualquiera de los tests teóricos.

Cómo usar esta muestra y cómo estudiar la Section 6

Estas 15 preguntas se apoyan en el razonamiento detrás de las normas más que en el vocabulario. Preguntan por qué vuelca antes el remolque que la tractora, por qué sueltas el freno en un derrape de remolque en vez de frenar más, qué pasa de verdad cuando se cruzan las glad hands y en qué orden van los pasos del acople. Esa es la parte que premia el test escrito, y también es la que te mantiene de pie en una rampa mojada de noche. Las preguntas mezclan los formatos que usa un test teórico, incluidos marcar todas las que correspondan y completar huecos, porque elegir tres respuestas correctas de cinco es una comprobación más dura y más honesta de lo que sabes que elegir una de cuatro.

Hazlo de una sentada y sin apuntes, después lee la explicación de todas las preguntas, también de las que acertaste. Trata una respuesta fallada como un tema, no como un dato suelto. Si fallaste la pregunta de las líneas de aire cruzadas y la de la tractor protection valve, vuelve y repasa entera la subsección de las líneas de aire, porque la línea de servicio y la de emergencia solo tienen sentido como pareja. Lo mismo pasa con el vuelco y la amplificación hacia atrás, que son dos vistas de un mismo problema, porque una carga alta y un remolque que colea acaban las dos con la caja de lado. Aquí no se puntúa ni se guarda nada en ningún sitio, así que no te cuesta nada hacerlo en frío y descubrir qué todavía no sabes.

Para los pasos del acople, leer no basta. Escribe de memoria los dieciséis pasos de acople y los diez de desacople, en orden, hasta que te salgan sin mirar, y después dilos en voz alta mientras das la vuelta a un camión de verdad, si tienes acceso a uno. El orden lleva dentro la lógica de seguridad, y la lógica es lo que hace que el orden se quede. Calzas las ruedas antes de colocar la tractora, bloqueas los frenos del remolque antes de meterte debajo, te metes debajo con una linterna y compruebas las mordazas antes de enchufar el cable eléctrico, y subes las patas de apoyo al final del todo. Acierta el orden y buena parte de las preguntas sueltas se contestan solas.

Cómo StudyPDF crea tests completos con tu propio material del CDL

Quince preguntas te enseñan dónde flojeas. Por sí solas no te preparan, y un banco de preguntas genérico se aleja de la redacción que usa el manual de tu estado, que es la redacción de la que sale tu test. Una vez que sabes tus áreas flojas, lo que necesitas después es volumen sobre esas áreas concretas, sacado de las páginas que te dieron a ti.

StudyPDF va por otro camino, parte de tu material. Subes el manual del CDL de tu estado, el dosier de la Section 6 de tu autoescuela o los apuntes que te dio tu instructor, y Bo, el agente de estudio, crea tests de práctica completos con esas páginas exactas. Cada pregunta sale de tu material y cada explicación cita de dónde viene la respuesta, así que puedes ir directo a la fuente cuando algo no te cuadre. Puedes generar tests nuevos tantas veces como quieras, centrarlos en un área como el acople y desacople o las líneas de aire, y seguir qué temas sigues fallando.

No tienes que subir nada para empezar. Si no tienes ningún archivo a mano, di solo un tema, por ejemplo acoplar una tractora con semirremolque, la tractor protection valve o cómo evitar los derrapes de remolque, y Bo escribe un test de práctica sobre eso. Eso ayuda cuando estás esperando el dosier de la autoescuela o estudias de un manual que solo tienes en papel. Empezar es gratis.