CDL Combination Test Questions and Answers 2025

CDL Combination Test Questions and Answers 2025: Our CDL combination vehicles practice test will help you to pass the tests for combination vehicles Endorsements written test (tractor-trailer, doubles, triples, straight truck and trailer). The Combination Test Questions and Answers is only to give you the minimum knowledge needed for a written test of combination vehicles.

Combination vehicles are usually heavier, longer, and require more driving skills than single commercial vehicles. This means that drivers of combination vehicles need more knowledge and skill than drivers of single vehicles. In this chapter, we talk about some important safety factors that apply specifically to combination vehicles.

CDL Combination Test Questions and Answers

Test Name	CDL Practice Test 2025
Language	English
License	Endorsements Permit
Total Questions	30 sample questions
Test For	Commercial Driver License
Test Preparation	Combination vehicles Endorsements
Country	USA
Explanation	No

0 votes, 0 avg

CDL Combination Vehicles Test

1 / 30

Fully loaded rigs are __________ times more likely to rollover in a crash than empty rigs

A) 8

B) 5

C) 10

D) 20

2 / 30

When lowering the landing gear of a loaded trailer,

A) lift the trailer off the fifth wheel.

B) lower the gear until it makes firm contact with ground.

C) urn the crank in high gear a few extra turns after the landing gear makes firm contact with ground.

D) turn the crank in low gear a few extra turns after the landing gear makes firm contact with ground.

3 / 30

The air leakage rate for a combination vehicle (engine off, brake off) should be less than _________ psi per minute

A) 3

B) 2

C) 4

D) 1

4 / 30

Which of the following is the correct definition of offtracking?

A) When a vehicle is turning the corner, the rear wheels follow a different path than the front wheels.

B) Keeping the front of the rig as close to the curb as possible to avoid entering other lanes.

C) When a vehicle is turning the corner, the front wheels and rear wheels follow the same path.

D) When a vehicle is turning the corner, the front wheels lead the rear wheels around the turn.

5 / 30

The “normal” position of the trailer air supply control is used for

A) pulling a trailer.

B) putting on the trailer emergency brake.

C) shutting the air off.

D) parking a trailer.

6 / 30

The tractor protection valve will close automatically if air pressure is low or in the range of

A) 11-19 psi

B) 0-10 psi

C) 20-45 psi

D) 46 psi or above

7 / 30

When parking trailers without spring brakes, use _________ to safely secure the vehicle.

A) the parking brake

B) the trailer hand brake

C) the emergency brakes

D) wheel chocks

8 / 30

When the wheels of a trailer lock up and the trailer begins to swing around ______ is likely to occur.

A) a rear wheel braking skid

B) offtracking

C) rollover

D) trailer jackknife

9 / 30

When coupling, the fifth wheel jaws should close around the __________________ of the kingpin.

A) bottom

B) middle

C) shank

D) head

10 / 30

When coupling a tractor and semitrailer, you must lock the kingpin into the fifth wheel. Which is the best way to check the connection?

A) Drive forward.

B) Back up and unlock the trailer brake.

C) Lock the trailer brakes and pull the tractor gently forward.

D) Lock the trailer brakes and pull the tractor quickly forward.

11 / 30

Why should the trailer glad hands be locked together or attached to “dead end,” or dummy, couplers when not in use?

A) To keep the service and emergency glad hands from getting mixed up

B) To prevent air from escaping

C) To keep dirt out of the lines

D) To keep air pressure normal

12 / 30

Which of the following is a coupling device used to connect the service and emergency air lines from the truck or tractor to the trailer?

A) The tractor protection valve

B) The relay valve

C) The trailer air supply control

D) Glad hands

13 / 30

Your trailer has begun to skid. You should

A) release the foot brake to get traction back.

B) turn hard in the direction of the skid.

C) use the trailer hand brake to straighten out the rig.

D) apply the foot brake hard, and come to a full stop.

14 / 30

In combination vehicles, the trailer service brake should be tested with the ________, but controlled in normal operation with the _________.

A) trailer air supply control; hand valve

B) trailer emergency valve; foot brake

C) foot brake; hand valve

D) hand valve; foot brake

15 / 30

Emergency lines on combination vehicles are often color coded to keep them from getting mixed up. The service lines are coded with the color __________, and the emergency lines are coded with the color __________ .

A) red . . . blue

B) red . . . black

C) blue . . . red

D) blue . . . yellow

16 / 30

After the tractor has coupled with the semitrailer, in what position should you put the front trailer supports, or landing gear, before driving away?

A) Partway up without the crank handle secured

B) Halfway up

C) On the ground

D) Fully raised with the crank handle safely secured

17 / 30

Which of the following may happen if the tractor protection valve doesn’t work right?

A) The engine may shut off.

B) Nothing will happen.

C) The pressure may rise in the trailer.

D) An air hose or trailer brake lead could drain all the air from the trailer and possibly cause a loss of control in the vehicle.

18 / 30

Failure to keep the _________ lubricated could cause steering problems because of friction between tractor and trailer.

A) fifth wheel plate

B) glad hands

C) trailer protection valve

D) air supply knob

19 / 30

What are the two purposes of the emergency air line on combination vehicles?

A) To supply air to the trailer air tanks and to connect the trailer air tank to the trailer air brakes

B) To supply air to the trailer air tanks and control the emergency brakes

C) To carry air, which is controlled by the foot brake only

D) To control the emergency brakes and carry air controlled by the foot brake

20 / 30

If the service and emergency air lines are crossed when hooking up an old trailer, what will happen?

A) You will be able to drive away, but you won’t have trailer brakes.

B) Water and dirt will enter the air lines.

C) The trailer spring brake will release.

D) Nothing will happen.

21 / 30

When coupling a tractor to a semitrailer, what should you hook up before backing under the trailer?

A) The emergency and service air lines

B) Nothing; you are ready to back up

C) The trailer air supply control

D) The tractor protection valve

22 / 30

To supply air to the trailer air tanks in a combination vehicle, you must

A) push in the trailer supply control.

B) press the trailer hand brake.

C) open the relay valve.

D) pull out the trailer air supply control.

23 / 30

When coupling with a semitrailer, back the tractor up

A) in front of the right wheel.

B) at an angle to the trailer.

C) slightly off the center of the trailer.

D) directly in front of the trailer.

24 / 30

The earliest and best way to recognize that your trailer has started to skid is by

A) carefully watching how other drivers are reacting to your vehicle.

B) seeing it in your mirrors.

C) feeling the rig “pull” to the right or left.

D) periodically applying the brakes to check for traction.

25 / 30

Which of the following reduces the risk of rollover?

A) None of the above

B) Loading the cargo on one side of the truck only

C) Keeping the cargo as close to the ground as possible

D) Changing lanes quickly

26 / 30

How much space should be between the upper and lower fifth wheel after coupling?

A) More than 1 foot

B) No space

C) 1 foot

D) 6 inches

27 / 30

The standard following distance behind other vehicles is at least

A) two seconds for each ten feet of vehicle length plus one second if going over 40 mph.

B) two seconds for each ten feet of vehicle length.

C) one second for each twenty feet of vehicle length.

D) one second for each ten feet of vehicle length plus another second if going over 40 mph.

28 / 30

What will happen if the service air line comes apart while you are driving a combination vehicle?

A) nothing is likely to happen until you put on your brakes

B) the emergency trailer brakes will come on

C) the trailer’s air tank will exhaust through the open line

D) nothing at all is going to happen

29 / 30

You are coupling a tractor and semitrailer, and ready to back your trailer under a semi-trailer. When is the trailer at the right height?

A) When the tractor and semitrailer are even

B) When the trailer is raised slightly by the tractor as the tractor is backed under it

C) When the trailer is raised high above the trailer as the tractor is backed under it

D) When the kingpin is lower than the fifth wheel

30 / 30

When should the trailer hand valve be used?

A) Only in an emergency

B) To test the trailer brake

C) To park the trailer

D) To drive the trailer

Your score is

The average score is 81%

CDL Knоwlеdgе Test (50 Questions Each)

School Bus Endorsement

Air Brakes Endorsement

Combination vehicles Endorsements

Doubles and Triples Endorsement

Tank Endorsement

Hazardous Material

Passenger Endorsement

Metal Coil Endorsement

CDL Metal Coil Endorsement Practice Test 2025