CDL – Combination Vehicle Practice Test Complete Questions And Answers

The air leakage rate for a combination vehicle (engine off, brakes on) should not be more than _ psi. 4

Under good driving conditions, you should leave at least one second of space between your vehicle and the vehicle ahead for every feet of your vehicle’s length. 10
Semi trailers made before 1975 that are equipped with air brakes: Often do not have spring brakes.
Air lines on a combination vehicle are often colored to keep them from getting mixed up. The emergency line is ; the service line is . Red; Blue
If the brakes did not release when you pushed the trailer air supply valve, you should: Check the air line connections.
You supply air to the trailer tanks by: Pushing in the trailer air supply valve.
What are the other names for the service air line? Control line and signal line.
When you turn suddenly while pulling doubles, which trailer is most likely to turn over? The rear trailer is twice as likely to turnover as the tractor.
After you have coupled the trailer, you should start to raise the landing gear by using: Low gear.
What gear should the tractor engine be in after you uncouple the trailer and are inspecting the trailer supports? Neutral.
Describe what the trailer air supply control does. It is used to supply the trailer with air, shut the air off, and apply the trailer emergency brakes.
You are coupling a tractor to a semi trailer. You have connected the air lines. Before backing under the trailer, you should: Supply air to the trailer system and then pull out the air supply knob.
When checking the trailer emergency brakes, make sure than the tractor protection control valve is placed in the position. Emergency. You are coupling a tractor to a semi trailer. You have backed up but are not under it. Before backing under the semi-trailer, you should hook-up: The emergency and service air lines. At night, when a vehicle is carrying a load that extends four feet or more beyond the rear of the body, there must be at the extreme end of the load Red lights.
How should you test the tractor-semi-trailer connection for security? Pull gently forward in low gear against the locked trailer brakes; then look at it carefully.
The tractor protection valve will close and the trailer brakes will come on when there is a major leak in the brake line. Emergency.
The hand valve should be used: To test the trailer brakes.
You are coupling a semi trailer to your tractor but have not yet backed under it. The trailer is at the right height if: It will be raised slightly when the tractor is backed under it.
When backing a tractor under a trailer, you should expect that: The trailer will be lifted slightly when the trailer tractor backs under it.
After you supply air to the trailer, make sure the air lines are not crossed and the trailer brakes are working. This is done by: Applying and releasing the trailer brakes and listening for brake sounds.
“What is the “”crack-the-whip”” effect?” When you make a quick lane change or sudden movement of your steering wheel, the rear trailer tends to swing out. The force of the rear trailer becomes amplified, causing it to roll over (rearward amplification).
Where should the tractor be when you inspect landing gear after uncoupling the trailer? With the tractor frame under the trailer.
“Which type of truck-trailer combination has the greatest chance of a “”crack-the-whip”” rollover?” A tractor pulling 3 trailers.
You should not back a tractor under a trailer until the whole air system is: At normal pressure.
When you drive a set of doubles, which shut-off valve must be closed in the last trailer? Back.
When connecting the glad hands, press the two seals together with the couplers at what angle to each other? 90 degrees.
When backing a tractor under a trailer, you should: Always use the lowest reverse gear.
You should use chocks when parking under a trailer without spring brakes because: If the air supply leaks away, there will be no brakes.
You should not use the trailer hand brake to straighten out a jackknifing trailer, because: The brakes on the trailer wheels caused the skid in the first place.
To unlock the fifth wheel, pull the release handle to the position. Open. The best way to tell if your trailer has started to skid is to: See it in your mirrors. Almost half of all truck driver deaths are caused by: Rollovers. What is a tractor jackknife? When you lock up the drive tires on the tractor and the tractor spins out sideways as the trailer continues to push forward. You are uncoupling a trailer. After you shut off the trailer air supply and lock the trailer brakes, you should: Back up gently to ease pressure on the fifth wheel locking jaws. When should you use chocks to park a trailer not equipped with spring brakes? Always. You cross the air lines when hooking up to an old trailer. What will happen? If the trailer has no spring brakes, you will be able to drive away but you won’t have trailer brakes. Which part of the kingpin should the locking jaws close around? The shank. The iron trailer supports are up, and the trailer is resting on the tractor. Make sure that: There is enough clearance between the tractor frame and the landing gear. After you lock the kingpin into the fifth wheel, you should check the connection by pulling: The tractor ahead gently with the trailer brakes locked. If you do not do the final air brake check for air leaks and fix them before driving: You could lose brakes while driving. For coupling to be completed, the safety catch for the fifth wheel locking lever must be: Over the locking lever. What is the emergency air line? Air lines that control the emergency brakes on combination vehicles. When coupling, the proper position of the fifth wheel is: Tilted down toward the end of the tractor. You should not use the trailer hand valve while driving because: Of the danger of making the trailer skid. The service line: Carries air to a relay valve that allows the trailer brakes to be applied quickly. When you get ready to back under the semi-trailer, you should line up: Directly in front of the trailer. Why should you make sure that the fifth wheel plate is greased as required? To prevent steering problems. In general, the higher your truck’s center of gravity, the: Easier it is to turnover. What is the emergency air line for? To engage the trailer brakes in case of air pressure loss. A trailer is most likely to jackknife when it is: Empty. Air and electrical lines from the tractor to the trailer should be: Secured, but with enough slack for turns. A tractor with a(n) ____ trailer requires the shortest amount of stopping distance. Fully loaded.
While you are driving a combination vehicle, if the service line comes apart but the emergency line stays together, what will happen right away? Nothing is likely to happen until you try to apply the brakes.
If you have coupled with a semi-trailer, where should the front trailer supports be before driving away? Fully raised with the crank handle secured in its bracket.
To stop a trailer skid, you should: Release the brakes.
Here are two things that a driver can do to prevent a rollover: Keep the cargo as close to the ground as possible, and: Go slowly around turns.
Glad hands are used to connect the: Service and emergency air lines from the truck or tractor to the trailer.
How long does it take a typical tractor trailer to clear a single railroad track? A double track? It takes 15 seconds to clear a single track and more than 15 seconds to clear a double track.
While you check if the rear trailer is securely coupled to the front trailer, the landing gear should be: Slightly raised.
Why should you lock the tractor glad hands (or dummy couplers) to each other when you are not towing a trailer? It will keep dirt and water out of the lines.
Trucks roll over more easily when fully loaded and are: Ten times more likely to roll over in a crash than empty rigs.
When you are uncoupling a loaded trailer, lower the landing gear until it: Makes firm contact with the ground.
The fifth wheel locking lever is not locked after the jaws close around the kingpin. This means that: The coupling is not right and should be fixed before you drive the coupled unit.
Compared with a straight truck or bus, there are _ things to inspect in combination vehicles. More.
You are driving a combination vehicle when the trailer breaks away, pulling apart both air lines. You would expect the trailer brakes to come on and: The tractor protection valve to close.
When should you use the hand valve to park a combination vehicle? Never.
The front trailer supports are up, and the trailer is resting on the tractor. Make sure that: There is enough clearance between the tractor frame and the landing gear.
How much space should there be between the upper and lower fifth wheel after coupling? None.
Before you back under a trailer, make sure that: Trailer brakes are locked.
What is the safest way for you to make a turn without entering another traffic lane? You should turn wide as you complete the turn.
After the trailer has been coupled to the tractor, the tractor protection control valve should be placed in what position? Normal.