CDL Combination Vehicles-øveprøve

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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
   Vis svar og forklaring

   Svar: 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
   Vis svar og forklaring

   Svar: 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
   Vis svar og forklaring

   Svar: 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
   Vis svar og forklaring

   Svar: 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
   Vis svar og forklaring

   Svar: 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
   Vis svar og forklaring

   Svar: 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
   Vis svar og forklaring

   Svar: 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
   Vis svar og forklaring

   Svar: 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
   Vis svar og forklaring

   Svar: 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?

    Vælg alle, der passer.

    • 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
    Vis svar og forklaring

    Svar: 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?

    Vælg alle, der passer.

    • 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
    Vis svar og forklaring

    Svar: 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?

    Vælg alle, der passer.

    • 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
    Vis svar og forklaring

    Svar: 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.

    Muligheder for felt 1: open, closed, removed

    Muligheder for felt 2: open, closed, capped

    Vis svar og forklaring

    Svar: 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 _____.

    Muligheder for felt 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

    Vis svar og forklaring

    Svar: 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 _____.

    Muligheder for felt 1: blue, red, green, yellow

    Muligheder for felt 2: blue, red, black

    Vis svar og forklaring

    Svar: 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.

Hvad combination vehicles-prøven faktisk dækker

Combination vehicles-prøven er en af de skriftlige teoriprøver, du tager hos din delstats kørekortkontor i USA, og hver eneste Class A-ansøger skal op i den. Den er adskilt fra general knowledge-prøven, adskilt fra air brakes-prøven og adskilt fra doubles and triples-påtegningen, så de fleste Class A-ansøgere ender med mindst tre skriftlige prøver, før de overhovedet rører en lastbil. Delstaterne skriver deres egne spørgsmålssæt ud fra den samme model CDL-manual, så antallet af spørgsmål, tidsgrænsen, gebyret og hvor hurtigt du kan gå om efter en dumpet prøve varierer fra delstat til delstat. Beståelsesgrænsen varierer ikke på samme måde. Føderale regler kræver, at du svarer rigtigt på mindst 80 procent af spørgsmålene på hver teoriprøve, så en delstat, der giver dig 20 spørgsmål, lader dig ramme fire forkert, og en delstat, der giver dig 50, lader dig ramme ti forkert.

Indholdet kommer fra Section 6 i din delstats CDL-manual, og det falder i fem dele. Driving combination vehicles safely dækker væltefare og tyngdepunkt, blød styring og crack the whip-effekten, at bremse tidligt, lave trailere der sætter sig fast på hævede jernbaneoverskæringer, trailerudskridning, at svinge bredt på grund af off-tracking, altså at trailerens hjul skærer hjørnet, og at bakke med trailer. Combination vehicle air brakes dækker trailerhåndbremsen, tractor protection valve, betjeningen af trailerens luftforsyning, service- og emergency-slangerne, glad hands, altså luftkoblingerne mellem bil og trailer, trailerens lufttanke og afspærringsventilerne. Antiblokeringsbremser får en kort del for sig selv, og det meste af den handler om, hvad ABS ikke gør for dig. Så kommer de nummererede trin til kobling og frakobling, og de ekstra punkter, der lægges til en rundering, når der er en trailer bagi.

Trinnene til kobling og frakobling fortjener den største del af din læsetid, for de dukker op to gange. De bliver spurgt om på den her skriftlige prøve, og senere skal du finde, røre ved og benævne koblingens dele højt under pre-trip-delen af køreprøven. To andre ting er værd at få styr på tidligt. Hent din egen delstats manual frem for en generisk PDF, for din delstat skriver sine spørgsmål ud fra den udgave, den selv udgiver, og ordlyden vil passe. Og find ud af, hvor du står med entry level driver training. Siden februar 2022 har føderale regler krævet uddannelse hos en udbyder på det føderale register, før du kan tage køreprøven til et første Class A-kørekort, og det er et selvstændigt trin ved siden af teoriprøverne.

Sådan bruger du smagsprøven, og sådan læser du Section 6

De her 15 spørgsmål læner sig op ad begrundelsen bag reglerne frem for gloserne. De spørger, hvorfor en trailer vælter før trækkeren, hvorfor du slipper bremsen i en trailerudskridning i stedet for at bremse mere, hvad der faktisk sker, når glad hands bliver byttet om, og hvilken rækkefølge koblingstrinnene har. Det er den del, den skriftlige prøve belønner, og det er også den del, der holder dig oprejst på en våd frakørsel om natten. Spørgsmålene blander de formater, en teoriprøve bruger, blandt andet vælg alle der passer og udfyld det tomme felt, for at plukke tre rigtige svar ud af fem er en hårdere og mere ærlig kontrol af, hvad du kan, end at plukke ét ud af fire.

Tag den i ét stræk uden noter, og læs derefter forklaringen til hvert spørgsmål, også dem du svarede rigtigt på. Behandl et forkert svar som et emne frem for et enkelt faktum. Missede du spørgsmålet om ombyttede luftslanger og spørgsmålet om tractor protection valve, så gå tilbage og repeter hele underafsnittet om luftslanger på én gang, for serviceslangen og nødslangen giver kun mening som et par. Det samme gælder væltefare og rearward amplification, som er to blikke på ét problem, for både et højt læs og en piskende trailer ender med kassen på siden. Intet her bliver bedømt eller gemt nogen steder, så det koster ikke noget at tage den kold og finde ud af, hvad du endnu ikke kan.

Til koblingstrinnene er det ikke nok at læse. Skriv de seksten koblingstrin og de ti frakoblingstrin ned efter hukommelsen, i rækkefølge, indtil du kan gøre det uden at kigge, og sig dem så højt, mens du går rundt om et rigtigt vogntog, hvis du har adgang til et. Rækkefølgen bærer sikkerhedslogikken, og logikken er det, der får rækkefølgen til at sidde fast. Du sætter stopklodser, før du placerer trækkeren, du låser trailerbremserne, før du bakker ind under, du kryber ind under med en lygte og tjekker låsekæberne, før du sætter el-kablet i, og du hæver støttebenene allersidst. Får du rækkefølgen rigtigt, besvarer en god del af de enkelte spørgsmål sig selv.

Sådan bygger StudyPDF fulde øveprøver ud fra dit eget CDL-materiale

Femten spørgsmål kan vise dig, hvor du vakler. De kan ikke gøre dig klar alene, og en generisk spørgsmålsbank driver væk fra den ordlyd, din egen delstats manual bruger, og det er den ordlyd, din prøve er skrevet ud fra. Når du kender dine svage områder, er det, du har brug for derefter, mængde på præcis de områder, hentet fra de sider, du faktisk har fået udleveret.

StudyPDF arbejder ud fra dit materiale i stedet. Du uploader din delstats CDL-manual, Section 6-hæftet fra din skole eller de noter, din underviser har givet dig, og Bo, studieagenten, bygger fulde øveprøver ud fra præcis de sider. Hvert spørgsmål bygger på dit materiale, og hver forklaring henviser til, hvor svaret kommer fra, så du kan slå direkte op i kilden, når noget ser skævt ud. Du kan lave nye prøver så tit du vil, holde dem på ét område som kobling og frakobling eller luftslangerne, og følge med i hvilke emner du bliver ved med at ramme forkert.

Du behøver ikke uploade noget for at komme i gang. Har du ingen fil ved hånden, så nævn et emne i stedet, for eksempel kobling af trækker og sættevogn, tractor protection valve eller hvordan man undgår trailerudskridning, så skriver Bo en øveprøve ud fra det. Det hjælper, når du venter på et hæfte fra skolen, eller når du læser i en manual, du kun har på papir. Gratis at komme i gang.