CDL combination vehicles practice test
25 questions, and 20 right clears the federal 80 percent bar. Each answer is tied to the rule it tests. No signup, no email.
25 questions, 40 minutes. The timer starts when you begin, and answers are shown at the end.
How the real New York exam is graded
New York DMV grades the written test on two conditions, and a paper has to meet both: at least 14 of the 20 questions right, and at least 2 of the 4 road sign questions right. A score of 14 or more still fails if 3 of the 4 sign questions are wrong. The car exam simulator here holds you to both, drawing exactly 4 road sign questions into every 20 question sitting. Class M uses the same 20 and 14, which is what the motorcycle paper runs at; it has no drawn sign questions to apply the sign condition to, so it is marked on the overall count only. DMV publishes no time limit for the office test and no rule ending it early, so the allowance on each paper is ours.
This paper allows 40 minutes. That allowance is ours, not a federal rule, because no published limit exists for this test.
Every question in this New York cdl combination vehicles, with answers
All 25 questions this paper draws from, each with the correct answer, why it is correct, and the federal regulation it was drafted against. The paper itself picks a randomized subset and shuffles the options, so reading the list through is review rather than a shortcut.
1. Rearward amplification means that in a quick lane change:
- Both units move identically
- The trailer lags behind harmlessly
- The tractor swings more than the trailer
- The rear trailer swings much more than the tractor, and can roll over (correct answer)
Answer: The rear trailer swings much more than the tractor, and can roll over. The crack-the-whip effect multiplies through each unit. A twin trailer can experience several times the sideways force the tractor does, which is why a sudden swerve rolls the rear trailer while the cab stays upright.
Source: FMCSA combination vehicle handling guidance
2. Which combination is most likely to roll over in an evasive maneuver?
- A set of doubles or triples (correct answer)
- A straight truck
- An empty tractor unit
- A tractor with a single loaded trailer
Answer: A set of doubles or triples. Each extra articulation point amplifies the movement. Doubles and triples need earlier, gentler steering inputs and more following distance than a single trailer for exactly this reason.
Source: FMCSA combination vehicle handling guidance
3. To reduce the risk of a rollover you should:
- Load cargo as high as possible
- Keep the load low and centered, and go slowly round curves (correct answer)
- Brake hard entering a bend
- Carry the load to one side
Answer: Keep the load low and centered, and go slowly round curves. A high center of gravity is what tips a trailer. Keep cargo low and centered, and remember that posted ramp speeds are set for cars: a loaded combination often needs well below them.
Source: FMCSA cargo securement and handling guidance
4. Off-tracking means that when turning, the rear wheels of a combination:
- Lift off the road
- Follow exactly the same path as the front
- Follow a tighter path than the front wheels (correct answer)
- Follow a wider path than the front wheels
Answer: Follow a tighter path than the front wheels. The trailer cuts the corner. The longer the vehicle, the more it cuts, which is why you approach a turn wide at the exit rather than swinging wide on entry.
Source: FMCSA combination vehicle handling guidance
5. A trailer skid is best corrected by:
- Braking harder
- Steering sharply the other way
- Applying the trailer hand valve
- Releasing the brakes to let the trailer wheels roll and grip again (correct answer)
Answer: Releasing the brakes to let the trailer wheels roll and grip again. A trailer skid begins with locked trailer wheels. Releasing the brakes lets them turn and regain traction, which is what allows the trailer to fall back in line. The hand valve does the opposite of what is needed.
Source: FMCSA skid control guidance
6. The two air lines running to a trailer are:
- Service and emergency (correct answer)
- Supply and return
- Upper and lower
- Primary and secondary
Answer: Service and emergency. The service line carries the pressure that applies the trailer brakes in proportion to the pedal. The emergency line supplies the trailer air tanks and controls the trailer emergency brakes.
Source: FMCSA combination vehicle guidance
7. Glad hands are color coded so that:
- Blue is emergency and red is service
- Blue is service and red is emergency (correct answer)
- Both are the same color
- Color varies by manufacturer
Answer: Blue is service and red is emergency. Blue for service, red for emergency. Crossing them means the trailer brakes will not work when you press the pedal, and you may not discover that until you need to stop.
Source: FMCSA combination vehicle guidance
8. The tractor protection valve exists to:
- Control trailer lights
- Regulate engine speed
- Keep tractor air if the trailer breaks away or a bad leak develops (correct answer)
- Apply the parking brake
Answer: Keep tractor air if the trailer breaks away or a bad leak develops. If the trailer separates or the emergency line fails, this valve closes to preserve enough air in the tractor for the tractor to stop itself. It normally closes somewhere between 20 and 45 psi.
Source: FMCSA combination vehicle guidance
9. If the trailer breaks away while driving, the trailer brakes:
- Apply only if you use the hand valve
- Release completely
- Do nothing
- Apply automatically as the emergency line loses air (correct answer)
Answer: Apply automatically as the emergency line loses air. Loss of pressure in the emergency line applies the trailer brakes automatically. That is the safety design, and it is why you never plug a leaking emergency line to keep driving.
Source: FMCSA combination vehicle guidance
10. Before backing under a trailer, the trailer brakes should be:
- Released
- Locked, using the parking brake or by chocking the wheels (correct answer)
- Applied with the foot pedal
- Disconnected
Answer: Locked, using the parking brake or by chocking the wheels. If the trailer can roll, the tractor pushes it backwards instead of coupling. Secure it first, and check the landing gear is set so the trailer nose is slightly lower than the fifth wheel.
Source: FMCSA coupling procedure
11. After coupling, you should test the connection by:
- Raising the landing gear fully first
- Looking at the fifth wheel only
- Locking the trailer brakes and gently pulling forward against them (correct answer)
- Sounding the horn
Answer: Locking the trailer brakes and gently pulling forward against them. The tug test proves the jaws have closed round the kingpin. Do it before raising the landing gear fully, so a failed coupling drops the trailer onto its legs rather than onto the frame.
Source: FMCSA coupling procedure
12. When you inspect the coupling, there should be:
- The kingpin resting on top of the fifth wheel
- The locking jaws open around the kingpin
- A visible gap between the trailer apron and the fifth wheel
- No gap between the trailer apron and the fifth wheel (correct answer)
Answer: No gap between the trailer apron and the fifth wheel. A gap means the trailer is riding on top of the fifth wheel rather than seated in it, and it can come apart. Get under with a flashlight and confirm the jaws are closed around the shank of the kingpin, not the head.
Source: FMCSA coupling inspection guidance
13. The fifth wheel locking jaws should close around:
- The shank of the kingpin (correct answer)
- The trailer apron
- The slider rails
- The head of the kingpin
Answer: The shank of the kingpin. Jaws round the head instead of the shank look coupled and will separate under load. This is one of the specific things a CDL examiner expects you to name during a pre-trip.
Source: FMCSA coupling inspection guidance
14. When uncoupling, you should lower the landing gear:
- After pulling the tractor clear
- Until it just touches the ground, then lower a little further to take some weight (correct answer)
- Only if the trailer is loaded
- Fully before disconnecting the air lines
Answer: Until it just touches the ground, then lower a little further to take some weight. Take some weight but do not lift the trailer off the fifth wheel: raising it makes the tractor hard to pull out and can damage the landing gear. Then disconnect the lines, release the fifth wheel and pull clear slowly.
Source: FMCSA uncoupling procedure
15. A converter dolly used to connect a second trailer must be:
- Positioned by hand only
- Left unbraked while coupling
- Secured so it cannot roll, with its own brakes or chocks (correct answer)
- Coupled with the air lines connected first
Answer: Secured so it cannot roll, with its own brakes or chocks. A dolly rolls easily and is heavy enough to injure. Chock it or charge its air to lock the brakes before you back onto it, and check the dolly tow bar aligns with the pintle before coupling.
Source: FMCSA doubles coupling guidance
16. On a combination, the front trailer supports the rear trailer through:
- The service line only
- The fifth wheel on the tractor
- The landing gear
- The pintle hook and dolly (correct answer)
Answer: The pintle hook and dolly. The dolly tow bar attaches to the pintle hook on the front trailer, and the dolly carries a fifth wheel for the rear trailer. Both connections need checking, and the safety chains as well.
Source: FMCSA doubles inspection guidance
17. When driving a set of doubles, the heavier trailer should be:
- Immediately behind the tractor (correct answer)
- It makes no difference
- Split evenly, which is impossible
- At the rear
Answer: Immediately behind the tractor. Put the heavier trailer first. A heavy trailer at the rear amplifies the whip effect and makes the set far more likely to roll in an evasive maneuver.
Source: FMCSA doubles operating guidance
18. A sliding fifth wheel is adjusted to:
- Change the trailer height
- Distribute weight correctly across the axles and control turning clearance (correct answer)
- Improve fuel consumption only
- Allow steeper ramps
Answer: Distribute weight correctly across the axles and control turning clearance. Sliding it changes axle loading, which matters for legal weight limits, and it changes how much room the trailer has to swing. Always confirm the locking pins are fully engaged after sliding.
Source: FMCSA weight distribution guidance
19. Before coupling the air lines you should:
- Charge the trailer first
- Leave the seals dirty, it does not matter
- Check the glad hand seals and clean them, then connect (correct answer)
- Connect the service line only
Answer: Check the glad hand seals and clean them, then connect. Damaged or dirty seals leak, and a leaking emergency line will not hold the trailer brakes off. Check the rubber, connect firmly, and confirm no leak once charged.
Source: FMCSA coupling procedure
20. You are inspecting a trailer with a landing gear crank handle. It should be:
- Secured in its holder before driving (correct answer)
- Removed and stored in the cab
- Left resting on the frame
- Left extended for easy access
Answer: Secured in its holder before driving. A loose crank handle catches passing traffic and cyclists and can come off. Securing it in the holder is a specific pre-trip item.
Source: FMCSA pre-trip inspection guidance
21. Following distance for a combination should be:
- The same as a car
- One second per 10 feet of length below 40 mph, plus a second above 40 mph (correct answer)
- Two seconds regardless
- Whatever the traffic allows
Answer: One second per 10 feet of length below 40 mph, plus a second above 40 mph. A 60 foot combination needs six seconds below 40 mph and seven above it. Combination vehicles cannot stop or swerve like a car, and the trailer decides what happens when you try.
Source: FMCSA space management guidance
22. An empty trailer, compared to a loaded one:
- Is more stable in crosswinds
- Always stops in a shorter distance
- Can bounce, lock up its wheels more easily and give poorer braking (correct answer)
- Handles identically
Answer: Can bounce, lock up its wheels more easily and give poorer braking. Less weight on the tires means less traction, and brakes designed for a load are too powerful for an empty trailer, so its wheels lock more readily. Empty rigs are also far more affected by crosswinds.
Source: FMCSA combination vehicle handling guidance
23. The correct order when coupling is closest to:
- Back under fast, raise gear, connect air, tug test
- Raise gear, back under, connect air
- Connect air lines, back under, secure trailer, raise gear
- Secure trailer, back under slowly, connect and charge air, tug test, raise gear (correct answer)
Answer: Secure trailer, back under slowly, connect and charge air, tug test, raise gear. Secure the trailer first so it cannot roll, back under slowly, connect and charge the air, tug test the coupling, inspect it visually, then raise the landing gear last. Raising the gear early removes your safety net.
Source: FMCSA coupling procedure
24. Safety chains on a converter dolly are there to:
- Hold the connection if the pintle hook fails (correct answer)
- Secure the cargo
- Ground the trailer
- Carry electrical current
Answer: Hold the connection if the pintle hook fails. They are the backup if the tow bar comes off the pintle hook. Check they are secured with no slack lying on the road, and that they are not worn or repaired with the wrong hardware.
Source: FMCSA doubles inspection guidance
25. When backing a combination, the trailer initially moves:
- In the same direction you turn the wheel
- In the opposite direction to the way you turn the wheel (correct answer)
- Straight regardless of steering
- Unpredictably
Answer: In the opposite direction to the way you turn the wheel. Turning the wheel left sends the trailer right, and vice versa. Back slowly, use small inputs, and get out and look whenever you lose sight of where the trailer is going.
Source: FMCSA backing guidance
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Original practice questions written from the rules themselves, not the examination questions New York DMV uses. New York DMVneither runs this site nor endorses it.