CDL Combination Vehicles Practice Test 1


A fully loaded rig is _________ times more likely to roll over in a crash than an empty rig.

Correct! Wrong!

10. When a truck has cargo, the center of gravity moves higher which increases the likelihood of rollover.

When following behind other vehicles, you should follow

Correct! Wrong!

At least one second for every 10 feet of your vehicle length, plus one second if going over 40 MPH. You should insure that you have a safe following distance to lessen the chance of making a sudden steering change.

A trailer jackknife is likely to happen when

Correct! Wrong!

The wheels of the trailer lock up. When the wheels of the trailer lock up, the trailer may swing around resulting in a trailer jackknife. Trailer jackknifes are more likely to happen when the trailer is empty or lightly loaded. When a vehicle has a high center of gravity, a rollover may happen. When there is too much weight on the steering axles, hard steering can occur.

What is the fastest and best way to recognize that your trailer has started to skid?

Correct! Wrong!

See it in your mirrors. The best and earliest way to determine that your trailer has started to skid is by seeing it in your mirrors. You should check your mirrors regularly, especially after applying the brakes hard.

If your trailer begins to skid, you should

Correct! Wrong!

Release your brakes until the trailer wheels grip the road again. If your trailer skids (jackknife) your best course of action is to release the brakes until you get traction back. You should not apply the trailer hand brakes, since the skid was caused by wheel lock up in the first place.

Which of the following will help prevent a rollover:

Correct! Wrong!

All of the above. Risk of rollover is increased by a high center of gravity. Keeping the cargo as close to the ground will lower the center of gravity and decrease the risk of rollover. Keeping the cargo centered and driving slowly around curves will also help reduce the risk of a rollover.

On the trailer air lines of a combination vehicle, the service line connects to the _________ on the trailer to control the pressure to the trailer brakes.

Correct! Wrong!

Relay valves. The service line is connected to the relay valves on the trailer to apply more or less pressure to the trailer brakes. They connect the trailer air tanks to the trailer air brakes. Glad hands connect tractor service and emergency lines to the trailer service and emergency lines. The trailer hand valve works the trailer brakes. The tractor protection valve control keeps air in the brake system in case the trailer breaks away or develops a bad leak.

On older trailers, what will happen if the emergency and service air lines are crossed?

Correct! Wrong!

You could drive away, but you will not have trailer brakes. Older trailers don't have spring brakes so if the air supply in the trailer air tanks has leaked away, there will be no emergency brakes.

When hoses are not in use, why should the trailer gland hands be locked together or attached to dead end or dummy couplers?

Correct! Wrong!

To keep the air supply clean. Coupling the glad hands together or using dummy couplers will prevent water and dirt from getting into the couplers and the air lines.

If the trailer protection valve malfunctions, which of the following may occur?

Correct! Wrong!

A leak or trailer break away could drain all the air from the brake system. The trailer protection valve's purpose is to keep air in the brake system in case the trailer brakes away or develops a bad leak. If the trailer protection valve malfunctions, then air could be drained away from the brake system.

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