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OR CDL Combination practice questions

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Question 1Combination Vehicle Inspection and Coupling/Uncoupling

During a pre-trip inspection of a combination vehicle, where should you check that the trailer's spring brakes are actually set and holding?

  1. By walking behind the trailer and listening for air leaks at the relay valve
  2. By watching the trailer brake chambers for a pushrod that stays extended
  3. By reading the tractor's air pressure gauge after building full pressure
  4. By attempting to rock the trailer with the tractor's engine off and the trailer parking brake applied Correct answer.

Explanation

The practical check for trailer spring brakes is to apply the trailer parking brake, shut off the engine, and try to pull or rock the combination gently; if the trailer holds, the spring brakes are functioning. A pushrod that stays extended actually indicates the brake is applied, but visually confirming it on every chamber is not the standard field check. Listening for leaks tests the air system, not whether the brakes hold.

Question 2Combination Vehicle Inspection and Coupling/Uncoupling

When coupling a tractor to a semitrailer, at what point should you back under the trailer before the fifth wheel engages the kingpin?

  1. Until the trailer's landing gear lifts clear of the ground
  2. Until the trailer apron contacts the rear of the tractor frame
  3. Until the fifth wheel just touches the trailer's upper plate
  4. Until the kingpin has fully locked into the fifth wheel jaws Correct answer.

Explanation

You back under until the fifth wheel jaws close and lock around the kingpin; only then is the coupling secure enough to test. Stopping earlier leaves the kingpin unlocked, which is the classic cause of a dropped trailer. Landing gear clearance and apron contact are not the criterion for a locked coupling.

Question 3Combination Vehicle Inspection and Coupling/Uncoupling

After coupling, you perform a tug test. What does a successful tug test demonstrate?

  1. That the trailer's spring brakes release when air is supplied
  2. That the fifth wheel jaws have closed and locked on the kingpin Correct answer.
  3. That the landing gear is fully raised and stowed
  4. That the trailer's air lines are properly connected and charging

Explanation

In a tug test you set the trailer parking brake, then pull gently forward against it. If the trailer does not move and the tractor does not pull free, the jaws are locked on the kingpin. The test does not verify air line charging, spring brake release, or landing gear position.

Question 4Combination Vehicle Inspection and Coupling/Uncoupling

You are preparing to uncouple a loaded semitrailer on level ground. Which step belongs in the correct sequence?

  1. Lower the landing gear until it contacts the ground, then pull forward slightly to confirm support
  2. Lower the landing gear to firm ground before releasing the fifth wheel and pulling clear Correct answer.
  3. Disconnect the air lines before setting the trailer parking brake
  4. Release the tractor parking brake before lowering the landing gear

Explanation

The landing gear must be lowered to firm ground and support the trailer before the fifth wheel is released and the tractor is pulled out. Releasing the tractor brake early or disconnecting air lines before setting the trailer brake can let the trailer roll or drop. Pulling forward to test support is not part of the uncoupling sequence.

Question 5Combination Vehicle Inspection and Coupling/Uncoupling

Why must the trailer's air lines be connected to the tractor with the glad hands matched to their correct color-coded couplers?

  1. To ensure the emergency line can supply the trailer and the service line can apply the brakes Correct answer.
  2. To keep the electrical cord from tangling with the air hoses
  3. To allow the trailer spring brakes to be released manually
  4. To prevent the trailer's ABS lamp from illuminating

Explanation

The emergency (supply) line charges the trailer system and releases the spring brakes, while the service line carries the control signal that applies the brakes. Cross-connecting them defeats both functions and can leave the trailer without brakes. Cable routing and ABS indication are unrelated to air line color matching.

Question 6Combination Vehicle Inspection and Coupling/Uncoupling

During a walk-around inspection, you find a trailer tire with a deep cut exposing cord. What is the correct action?

  1. Note it and continue, since trailer tires are not part of the inspection
  2. Inflate the tire to maximum sidewall pressure and proceed
  3. Reduce speed and monitor it during the trip
  4. Remove the vehicle from service until the tire is replaced Correct answer.

Explanation

A cut deep enough to expose cord means the tire is structurally compromised and cannot be safely run; the vehicle must be placed out of service until it is replaced. Trailer tires are fully part of the pre-trip inspection. Inflating an already damaged tire does not restore it and risks a blowout.

Question 7Combination Vehicle Inspection and Coupling/Uncoupling

You are checking the fifth wheel before coupling. Which condition should cause you to reject the coupling?

  1. The fifth wheel plate is lightly greased
  2. The mounting bolts are tight and show no rust
  3. The jaws are open and the release handle is pulled out Correct answer.
  4. The jaws are closed with the safety latch engaged

Explanation

For coupling, the jaws must be open with the release handle out so the kingpin can enter and lock. A closed jaw with the latch engaged is the post-coupling condition, not the pre-coupling setup. Grease and tight, rust-free bolts are acceptable conditions.

Question 8Combination Vehicle Inspection and Coupling/Uncoupling

When should you use the trailer hand valve (trolley valve) while driving a combination vehicle?

  1. To release the trailer spring brakes after coupling
  2. To test the trailer brakes, never as a parking brake Correct answer.
  3. To hold the combination on a hill while you exit the cab
  4. To replace the foot brake during normal stops

Explanation

The trailer hand valve is intended for testing that trailer brakes apply; it should not be used as a parking brake because it can leak off and release. Normal stopping is done with the foot brake, and spring brakes are released by supply air, not the hand valve. Using it to hold a vehicle unattended is dangerous.

Question 9Combination Vehicle Inspection and Coupling/Uncoupling

What is the purpose of the trailer's spring brakes in a combination vehicle?

  1. To hold the trailer only while the engine runs
  2. To provide the service braking during normal stops
  3. To modulate braking on slippery surfaces
  4. To apply automatically if supply air is lost Correct answer.

Explanation

Spring brakes are held off by air pressure; if supply air drops or lines separate, the springs apply the brakes automatically, providing a fail-safe. Service braking is done by the service brake system, not the springs. They hold regardless of engine operation once applied.

Question 10Combination Vehicle Inspection and Coupling/Uncoupling

During your pre-trip inspection you check the coupling by looking at the fifth wheel from the side. What should you confirm?

  1. That the air lines are routed over the catwalk
  2. That the release handle is pulled fully out
  3. That the fifth wheel jaws are closed around the kingpin and the safety latch is engaged Correct answer.
  4. That the trailer frame is resting on the tractor's frame rails

Explanation

A visual check confirms the jaws are closed on the kingpin and the safety latch is in place, which supports the tug test. The trailer should rest on the fifth wheel, not on the tractor frame. A handle pulled out signals an unlocked coupling.

Question 11Combination Vehicle Inspection and Coupling/Uncoupling

You must inspect the air system of a combination vehicle before driving. Which check best confirms the tractor protection valve is working?

  1. Drain the wet tank and observe the compressor cycling
  2. Charge the system, then trip the trailer air supply valve and confirm the trailer spring brakes set Correct answer.
  3. Watch the low air warning buzzer activate below 60 psi
  4. Build full pressure, shut off the engine, and listen for leaks at the glad hands

Explanation

Tripping the trailer air supply valve simulates a loss of supply to the trailer; a working tractor protection valve then closes and the trailer spring brakes apply, so the trailer brakes hold. Leak listening tests connections, the low-air warning tests the alarm, and draining tanks tests the compressor and drains.

Question 12Combination Vehicle Inspection and Coupling/Uncoupling

When backing a tractor-semitrailer, which technique helps you keep the trailer tracking where you want it?

  1. Steer toward the direction you want the trailer to go
  2. Steer opposite the direction you want the trailer to go Correct answer.
  3. Accelerate briskly to shorten the turning radius
  4. Hold the wheel straight and use only the trailer hand valve

Explanation

When backing a trailer, you turn the steering wheel opposite the direction you want the trailer to travel, then follow the trailer with the tractor. Steering toward the desired trailer direction is the instinct that causes jackknifing. The hand valve is for brake testing, and brisk acceleration reduces control.

Question 13Combination Vehicle Inspection and Coupling/Uncoupling

What does the red (emergency) glad hand supply to the trailer?

  1. The electrical power for trailer lights
  2. The ABS sensor signal
  3. The service brake control signal
  4. The supply air that charges the trailer system and releases spring brakes Correct answer.

Explanation

The red emergency line supplies air that charges the trailer reservoirs and pushes off the spring brakes; losing it causes the springs to apply. The blue service line carries the brake application signal. Electrical power and ABS signals travel through the cord, not the air lines.

Question 14Combination Vehicle Inspection and Coupling/Uncoupling

You are coupling and notice the trailer kingpin is greasy but the fifth wheel jaws appear dry. What is the appropriate action?

  1. Apply grease to the fifth wheel plate and jaws as needed for proper lubrication Correct answer.
  2. Wipe all grease from the kingpin to prevent slipping
  3. Spray the jaws with solvent to remove any film
  4. Proceed without lubrication since the kingpin is already greased

Explanation

The fifth wheel plate and jaws need adequate lubrication so the trailer pivots and the jaws lock and release smoothly; a dry jaw can wear or stick. The kingpin being greasy does not lubricate the jaws. Removing grease or solvent-washing the jaws increases wear and sticking.

Question 15Combination Vehicle Inspection and Coupling/Uncoupling

Before lowering the landing gear during uncoupling, what should you confirm about the ground?

  1. That the surface is sloped so water drains away
  2. That the surface is gravel so the gear sinks for stability
  3. That the surface is firm and level enough to support the loaded trailer Correct answer.
  4. That the surface is freshly paved so the gear will not move

Explanation

Landing gear must rest on firm, level ground that can carry the trailer's weight; soft or sloped ground can let the gear sink or the trailer roll. Slopes are specifically to be avoided when uncoupling. Gravel that lets the gear sink and fresh pavement are not stability advantages.

Question 16Combination Vehicle Inspection and Coupling/Uncoupling

After uncoupling, why should you place wheel chocks at the trailer wheels?

  1. To keep the air lines from dragging on the ground
  2. To prevent the uncoupled trailer from rolling Correct answer.
  3. To keep the fifth wheel jaws from closing
  4. To hold the landing gear in the raised position

Explanation

Once the tractor is removed, only the trailer parking brake and landing gear resist movement; chocks provide an additional safeguard against rolling, especially on any grade. Chocks do not affect air lines, landing gear position, or fifth wheel jaws.

Question 17Combination Vehicle Inspection and Coupling/Uncoupling

You are inspecting the sliding fifth wheel and find the locking pins are not fully engaged after adjustment. What is the risk if you drive?

  1. The fifth wheel can slide under load, changing weight distribution and control Correct answer.
  2. The trailer spring brakes will not release
  3. The trailer lights will not function
  4. The glad hands will disconnect

Explanation

Sliding fifth wheel locking pins must be fully seated so the wheel cannot move; if they are not engaged, the fifth wheel can shift under load, altering axle loading and handling. Lights, spring brake release, and glad hand connection are unrelated to the locking pins.

Question 18Combination Vehicle Inspection and Coupling/Uncoupling

During a pre-trip inspection, how do you check that the trailer service brakes apply?

  1. Release the tractor parking brake and roll forward
  2. Turn on the trailer ABS lamp and watch it flash
  3. Press the foot brake and have someone watch the trailer brake chambers or listen for application Correct answer.
  4. Pull the red air supply knob and watch the tractor gauge

Explanation

With the system charged, applying the foot brake sends the service signal to the trailer; observing pushrods extend or hearing the chambers apply confirms the trailer service brakes work. Pulling the red knob tests the emergency/spring brake function, and the ABS lamp is a diagnostic indicator.

Question 19Combination Vehicle Inspection and Coupling/Uncoupling

What is the correct order for connecting a tractor to a trailer's electrical and air lines after the kingpin is locked?

  1. Connect the electrical cord first, then the service and emergency air lines Correct answer.
  2. Connect the service line, then the emergency line, then the electrical cord
  3. Connect the emergency line, then the electrical cord, then the service line
  4. Connect the air lines and electrical cord in any order since they are independent

Explanation

After coupling, the electrical cord is connected first so trailer lights and ABS have power, then the service (blue) and emergency (red) air lines are connected and the trailer supply valve opened. The order matters for safe checks and consistent procedure. There is a standard sequence rather than an arbitrary one.

Question 20Combination Vehicle Inspection and Coupling/Uncoupling

You notice the trailer's spring brake chambers have a caged (released) spring on one wheel. What does this indicate?

  1. The ABS is active on that wheel
  2. The brake is applied and functioning normally
  3. The trailer is overloaded on that axle
  4. The spring brake has been manually released and that wheel may not hold Correct answer.

Explanation

Caging a spring brake mechanically compresses the spring to release the brake, often to move a vehicle with an air problem; if left caged, that wheel's parking/emergency brake will not hold. It says nothing about axle loading or ABS activity. A normally applied brake is not caged.

Question 21Combination Vehicle Inspection and Coupling/Uncoupling

When performing a pre-trip inspection of the coupling, which item confirms the trailer is resting properly on the fifth wheel?

  1. The trailer apron is above the fifth wheel plate with a visible gap
  2. The air lines hang below the trailer frame
  3. The trailer apron sits flat against the fifth wheel plate with no gap Correct answer.
  4. The landing gear touches the ground

Explanation

A properly coupled trailer sits flat on the fifth wheel plate with the apron in full contact and no gap; a gap can mean the kingpin is not fully seated. Landing gear contact and air line position do not indicate proper seating on the fifth wheel.

Question 22Combination Vehicle Inspection and Coupling/Uncoupling

Why should you avoid using the trailer hand valve to hold a combination vehicle stopped at a long red light?

  1. It can leak off and release, letting the vehicle roll Correct answer.
  2. It overheats the tractor's service brakes
  3. It causes the trailer ABS to engage
  4. It disables the tractor protection valve

Explanation

The hand valve is not a parking brake; air can bleed off over time and the brakes release, allowing the vehicle to roll. Holding with the foot brake or setting the parking brake is correct. The hand valve does not engage ABS, overheat service brakes, or disable the protection valve.

Question 23Combination Vehicle Inspection and Coupling/Uncoupling

During your pre-trip inspection you find the trailer's electrical cord plug has corroded pins. What is the proper response?

  1. Coat the pins with grease and proceed
  2. Clean or replace the plug so lights and ABS work reliably Correct answer.
  3. Tape over the plug and rely on the tractor lights
  4. Ignore it since trailer lights are optional

Explanation

Corroded pins can cause intermittent or failed trailer lights and ABS power, which are safety and legal requirements; the plug should be cleaned or replaced. Greasing corroded pins does not restore contact, taping disables the circuit, and trailer lights are required.

Question 24Combination Vehicle Inspection and Coupling/Uncoupling

You are about to couple to a trailer whose landing gear is only partly raised. Why does this matter during coupling?

  1. Partly raised gear can contact the ground or tractor and interfere as you back under Correct answer.
  2. It changes the trailer's brake timing
  3. Low landing gear prevents the kingpin from entering the fifth wheel
  4. It disables the trailer's ABS

Explanation

Landing gear must be raised enough to clear the ground and the tractor as you back under; gear left down can catch on the ground or frame and damage equipment or prevent proper coupling. It does not affect brake timing or ABS. The kingpin height, not gear height, governs entry into the jaws.

Question 25Combination Vehicle Inspection and Coupling/Uncoupling

What is the purpose of the trailer air supply (red) knob in the cab?

  1. To supply or cut off air to the trailer, controlling spring brake release Correct answer.
  2. To apply only the trailer service brakes for testing
  3. To release the tractor parking brake
  4. To adjust trailer ABS sensitivity

Explanation

The red trailer air supply knob controls air to the trailer; pushed in it charges the trailer and releases the spring brakes, pulled out it cuts supply and the trailer spring brakes apply. It does not apply service brakes alone, release the tractor parking brake, or adjust ABS.

Question 26Combination Vehicle Inspection and Coupling/Uncoupling

You are preparing to couple a tractor to a semitrailer. At what height should the trailer apron sit relative to the fifth wheel before you back under it?

  1. High enough that the trailer will be raised slightly when the tractor backs under it Correct answer.
  2. Level with the top of the tractor frame rails
  3. Slightly lower than the fifth wheel so the trailer lifts as you back in
  4. As low as possible so the kingpin clears the jaws

Explanation

The trailer should be raised so the fifth wheel will lift it slightly as you back under, which lets the kingpin settle fully into the jaws and the trailer rest solidly on the plate. If the trailer is too low, the kingpin can strike the fifth wheel or the tractor can pass under without locking. If it is too high, the kingpin may skip over the jaws.

Question 27Combination Vehicle Inspection and Coupling/Uncoupling

After backing under a trailer and hearing the fifth wheel lock, you tug-test the coupling. What does a proper tug test involve?

  1. Pull forward gently in a low gear with the trailer brakes released and feel for resistance
  2. Reverse a short distance with the trailer brakes set and watch the gap close
  3. Pull forward firmly with the trailer spring brakes set and confirm the tractor does not move away Correct answer.
  4. Release the tractor parking brake and let the rig roll forward a few feet in neutral

Explanation

A tug test is done with the trailer spring brakes applied: you pull forward gently against them and confirm the tractor is held back by a locked kingpin. If the jaws are not closed, the tractor will pull out from under the trailer. This confirms the lock before you raise the landing gear or connect lines.

Question 28Combination Vehicle Inspection and Coupling/Uncoupling

You are uncoupling on a slight slope. Which sequence protects you and the equipment?

  1. Chock the trailer wheels, lower the landing gear to firm ground, release the trailer spring brakes, then pull the tractor out Correct answer.
  2. Lower the landing gear, chock the trailer wheels, release the tractor parking brake, then pull out slowly
  3. Release the trailer brakes, lower the landing gear, then pull out with the tractor brake released
  4. Pull the tractor out first, then lower the landing gear and chock the wheels

Explanation

Chocking first prevents the trailer from rolling once the spring brakes are released. The landing gear must be down on firm ground and supporting the trailer before the tractor is pulled out, so the trailer does not drop. Only then should the tractor be eased out from under the trailer.

Question 29Combination Vehicle Inspection and Coupling/Uncoupling

When coupling, assume the manufacturer's procedure calls for connecting the trailer's supply line first. Which glad hand should you connect first, and why?

  1. The electrical cord first, because the trailer lights must work before air is connected
  2. The blue (service) line first, because it charges the trailer tank
  3. The red (emergency) line first, because it supplies air and releases the trailer spring brakes Correct answer.
  4. Either line, because the couplers are interchangeable

Explanation

Under the stated manufacturer procedure, the red emergency line is connected first because it is the trailer supply line. Charging the trailer air system releases its spring brakes. The blue service line carries the service-brake control signal; it does not charge the trailer tanks.

Question 30Combination Vehicle Inspection and Coupling/Uncoupling

You are inspecting the coupling from the side after backing under the trailer. What confirms the trailer is properly seated on the fifth wheel?

  1. The gap between the trailer apron and the fifth wheel is closed and the plate sits flat against the trailer Correct answer.
  2. The kingpin is visible below the fifth wheel
  3. The landing gear is still touching the ground
  4. The tractor frame is level with the trailer frame

Explanation

A correct coupling shows no gap between the trailer apron and the top of the fifth wheel, with the plate flat against the trailer. A visible gap means the trailer is riding on the kingpin or jaws rather than the plate. The landing gear should be raised clear before you drive.

Question 31Combination Vehicle Inspection and Coupling/Uncoupling

During a pre-trip inspection you find the fifth wheel jaws will not close fully around the kingpin. What is the correct action?

  1. Apply grease to the jaws and try again while backing
  2. Do not couple; correct the jaw or locking mechanism before use Correct answer.
  3. Raise the trailer higher and back under faster
  4. Couple anyway and let the weight of the trailer close the jaws

Explanation

Jaws that will not close fully mean the coupling cannot lock, and driving with an unlocked fifth wheel can let the trailer separate. The defect must be corrected before coupling. Grease or force will not fix a bent or damaged locking mechanism.

Question 32Combination Vehicle Inspection and Coupling/Uncoupling

Which air-line color connects the tractor's service brake signal to the trailer?

  1. Yellow
  2. Red
  3. Green
  4. Blue Correct answer.

Explanation

The blue line is the service line, carrying the brake application signal from the tractor to the trailer. The red line is the emergency/supply line. Confusing the two can leave the trailer without supply air or without service braking.

Question 33Combination Vehicle Inspection and Coupling/Uncoupling

You are checking the trailer spring brakes before a trip. Which result shows they are working?

  1. With the parking brake released, the trailer wheels lock
  2. With supply air charged, the trailer wheels turn freely when pushed
  3. With the service brake applied, the trailer wheels lock
  4. With supply air removed, the trailer wheels are locked Correct answer.

Explanation

Spring brakes are held applied by spring force and released by air pressure. Removing supply air should therefore lock the trailer wheels. This confirms the emergency braking function works if the lines separate.

Question 34Combination Vehicle Inspection and Coupling/Uncoupling

What is the purpose of the tractor protection valve in a combination vehicle?

  1. It balances air between the tractor and trailer tanks
  2. It limits tractor air pressure to the trailer to a safe maximum
  3. It releases the trailer spring brakes when the red knob is pulled
  4. It closes the tractor air supply to the trailer if pressure drops, protecting the tractor's brakes Correct answer.

Explanation

The tractor protection valve senses low air pressure and closes off the trailer supply, keeping enough air in the tractor to stop it. It also helps set the trailer spring brakes when the lines separate. It does not regulate maximum pressure or balance tanks.

Question 35Combination Vehicle Inspection and Coupling/Uncoupling

You are inspecting the sliding fifth wheel and find the locking pins are not fully engaged after adjustment. What should you do?

  1. Remove the pins to allow free adjustment
  2. Drive slowly and let the pins seat under load
  3. Leave them partly engaged because the weight holds the slide
  4. Engage the pins fully and confirm they are locked before driving Correct answer.

Explanation

The locking pins must be fully engaged and locked to hold the fifth wheel in position. Partly engaged pins can allow the fifth wheel to slide under load, which is dangerous. The pins must be confirmed locked before the vehicle is moved.

Question 36Combination Vehicle Inspection and Coupling/Uncoupling

During a walk-around, you find the trailer's electrical cord plug has corroded pins. What is the proper response?

  1. Replace or repair the plug before driving Correct answer.
  2. Plug it in and wiggle it until contact is made
  3. Tape over the plug and rely on the tractor lights
  4. Clean the pins and continue if the lights work

Explanation

Corroded pins can cause intermittent or failed trailer lights, which is a safety defect. The plug should be repaired or replaced before the trip. Taping or wiggling does not correct the underlying corrosion.

Question 37Combination Vehicle Inspection and Coupling/Uncoupling

You notice one trailer spring brake chamber has a caged (released) spring. What does this indicate?

  1. The spring brake on that wheel is mechanically released and will not apply Correct answer.
  2. The chamber has been upgraded for heavier loads
  3. The service brake on that wheel is over-adjusted
  4. The trailer is ready for normal operation

Explanation

Caging a spring brake manually compresses and holds the spring so the brake is released. A caged chamber will not apply its spring brake, so that wheel loses emergency/parking braking. It must be corrected before the trailer is used.

Question 38Combination Vehicle Inspection and Coupling/Uncoupling

When should you use the trailer hand valve (trolley valve) while driving?

  1. To hold the vehicle at a long red light
  2. To park the combination on a slope
  3. To slow the vehicle on a downgrade
  4. To test the trailer brakes during a pre-trip check Correct answer.

Explanation

The trailer hand valve is intended for testing trailer brakes, not for driving or parking. Using it to hold the vehicle can cause the trailer brakes to overheat or the combination to jackknife. Parking should rely on the spring/parking brakes.

Question 39Combination Vehicle Inspection and Coupling/Uncoupling

You are coupling and the trailer kingpin is greasy while the fifth wheel jaws appear dry. What is the appropriate action?

  1. Wipe the kingpin dry and couple without lubricant
  2. Couple as is and grease the jaws later
  3. Add grease only to the trailer apron
  4. Clean the kingpin and apply a light film of grease to the jaws before coupling Correct answer.

Explanation

The kingpin and jaws need a light film of lubricant to allow proper locking and release. Excess grease on the kingpin alone can collect dirt, so the jaws should also be lubricated. Coupling dry risks wear and difficulty uncoupling.

Question 40Combination Vehicle Inspection and Coupling/Uncoupling

Which check best confirms the trailer service brakes apply when you press the brake pedal?

  1. Check that the red knob stays pushed in
  2. Listen for air escaping at the glad hands
  3. Watch the trailer lights come on
  4. Have someone watch the trailer wheels while you apply the brakes with the engine running and air charged Correct answer.

Explanation

With air charged and the engine running, applying the brake pedal should apply the trailer service brakes, which can be confirmed by watching the wheels or brake chambers. Lights and knob position do not prove the brakes apply. Air escaping at the glad hands indicates a leak, not brake application.

Question 41Driving Combination Vehicles Safely (turns, braking, speed, space)

When you drive a tractor-trailer combination, which of the following is the main reason the vehicle needs a longer stopping distance than a passenger car?

  1. The combination weighs far more and its air brakes take time to apply at each wheel Correct answer.
  2. The engine brake automatically engages whenever the clutch is pressed
  3. The trailer tires are smaller and spin faster at highway speed
  4. The steering axle carries most of the weight, so the front tires grip poorly

Explanation

A loaded combination can weigh many times more than a car, and momentum rises with weight, so more distance is required to stop. In addition, air brake systems have a lag while pressure travels to each brake chamber, adding to total stopping distance.

Question 42Driving Combination Vehicles Safely (turns, braking, speed, space)

What is the correct way to make a right turn in a large combination vehicle?

  1. Start the turn from the rightmost lane and keep the rear wheels close to the curb
  2. Swing wide to the left before the turn, then bring the trailer close to the right curb
  3. Turn from the lane position that keeps the rear wheels from off-tracking over the curb Correct answer.
  4. Approach in the left lane and cut sharply across the right lane as you turn

Explanation

Because the rear wheels of a long combination track inside the path of the front wheels, you must set up the turn so the trailer's rear wheels clear the curb and any objects at the corner. This usually means approaching from a position that may be slightly left of the normal lane, then turning wide enough to protect the rear of the vehicle.

Question 43Driving Combination Vehicles Safely (turns, braking, speed, space)

You are driving a combination vehicle and need to make a left turn at an intersection. What lane position should you use as you approach?

  1. Approach in the rightmost lane and turn from there
  2. Approach in the lane just to the right of the center line or turning lane Correct answer.
  3. Approach as far left as possible, even crossing the center line
  4. Approach straddling two lanes so no one can pass on either side

Explanation

For a left turn, position the combination in the proper left-turn lane or the lane immediately right of the center line so the trailer has room to follow without crossing into oncoming traffic. Do not cross the center line or block multiple lanes unnecessarily.

Question 44Driving Combination Vehicles Safely (turns, braking, speed, space)

Why must you avoid braking hard on a curve while driving a combination vehicle?

  1. Hard braking on a curve has no effect on a combination vehicle
  2. Hard braking on a curve can cause the trailer to swing out or the combination to skid Correct answer.
  3. Hard braking on a curve is required to keep the trailer from off-tracking
  4. Hard braking shortens the wheelbase and improves the turning radius

Explanation

Braking hard while turning reduces tire traction available for steering and can cause the trailer to swing out or the whole combination to skid. The safe practice is to slow down before the curve and maintain a steady speed through it.

Question 45Driving Combination Vehicles Safely (turns, braking, speed, space)

What is the recommended following distance for a combination vehicle traveling at highway speeds under ideal conditions?

  1. One second total regardless of speed
  2. Four seconds for every 20 feet of vehicle length
  3. One second for each 10 feet of vehicle length Correct answer.
  4. Two seconds total at all speeds

Explanation

A common rule is to allow at least one second of following distance for each 10 feet of vehicle length at speeds below 40 mph, and to add one extra second for speeds above 40 mph. This gives the driver time to react and stop the heavier vehicle.

Question 46Driving Combination Vehicles Safely (turns, braking, speed, space)

When driving a combination vehicle, what is the safest way to handle a downgrade on a long mountain pass?

  1. Ride the brakes continuously to hold a steady speed
  2. Use a low gear and let the engine brake help control speed Correct answer.
  3. Accelerate to build momentum before the grade
  4. Shift to neutral and coast to save fuel

Explanation

On a long downgrade, select a low gear before starting down and let engine braking help control speed, applying the service brakes only as needed. Coasting in neutral or riding the brakes can lead to overheating and brake fade.

Question 47Driving Combination Vehicles Safely (turns, braking, speed, space)

What does the term 'off-tracking' mean for a combination vehicle?

  1. The vehicle's speed increases on a downhill grade
  2. The trailer disconnects from the tractor during a turn
  3. The front wheels drift to the outside of a turn
  4. The trailer wheels follow a path inside the path of the front wheels Correct answer.

Explanation

Off-tracking occurs because the rear wheels of a long combination cut inside the path traced by the front wheels during a turn. Drivers must allow for this by turning wide enough to keep the trailer's rear wheels clear of curbs and objects.

Question 48Driving Combination Vehicles Safely (turns, braking, speed, space)

Why should you avoid sudden lane changes when driving a combination vehicle at highway speed?

  1. Sudden lane changes have no effect on trailer stability
  2. Sudden lane changes improve fuel economy by reducing drag
  3. Sudden lane changes can cause the trailer to sway or the combination to roll over Correct answer.
  4. Sudden lane changes are required to keep the trailer aligned

Explanation

A combination vehicle has a high center of gravity and a long trailer, so abrupt steering inputs can cause the trailer to sway or the vehicle to roll over. Smooth, gradual lane changes keep the combination stable.

Question 49Driving Combination Vehicles Safely (turns, braking, speed, space)

You are driving a combination vehicle and approaching a sharp curve. What is the best way to manage your speed?

  1. Shift to neutral and coast through the curve
  2. Maintain highway speed and brake firmly in the middle of the curve
  3. Accelerate through the curve to keep the trailer tight
  4. Slow down before entering the curve and maintain a steady speed through it Correct answer.

Explanation

The safe technique is to reduce speed before the curve, then hold a steady speed through it so the tires retain traction for steering. Braking hard in the curve or coasting in neutral reduces control.

Question 50Driving Combination Vehicles Safely (turns, braking, speed, space)

When you must stop a combination vehicle on a downgrade, what is the recommended practice?

  1. Stop by turning off the engine and coasting to a halt
  2. Stop with the service brakes and set the parking brake, then release the service brakes Correct answer.
  3. Stop with the engine brake only and leave the transmission in neutral
  4. Stop with the trailer brakes only and keep the tractor brakes released

Explanation

On a downgrade, stop using the service brakes, set the parking brake, and then release the service brakes so the parking brake holds the vehicle. This prevents the vehicle from rolling and avoids relying on overheated service brakes.