1
Texas CDL Section 6 Combination
Vehicles Questions and Correct
Answers
1. What are the two things a driver can do to prevent a rollover?
Keep the cargo as close to the ground as possible to lower the center of gravity, and
drive slowly around turns.
2. Why should you never use the trailer hand valve while driving?
Using it while driving can cause the trailer wheels to skid, which could lead to a
jackknife. You should only use it to test the trailer brakes.
3. What is "off tracking" or "cheating"?
It is when a vehicle goes around a corner and the rear wheels follow a different path
than the front wheels. This is why you must swing wide on turns.
4. Describe what the trailer air supply control does.
When pushed in, it supplies air to the trailer brake system. When pulled out, it shuts
off the air supply and applies the trailer emergency brakes.
5. What is the emergency air line for?
It has two purposes: it supplies air to the trailer air tanks, and it controls the
emergency brakes on combination vehicles.
6. Describe what the service line is for.
The service line (usually blue) carries air, which is controlled by the foot brake or
the trailer hand brake, to apply the service brakes on the trailer.
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7. Where are the shut-off valves (cut-out cocks) located?
They are located at the back of trailers, where the air lines connect, and are used
when towing other trailers.
8. How can you test the tractor protection valve?
Charge the system, shut off the engine, and pump the brake pedal to reduce air
pressure. The trailer air supply control should pop out (go into emergency position)
when pressure falls to the manufacturer's specification (usually between 20-45
psi).
9. How do you test the trailer emergency brakes?
Charge the system with the trailer air supply pushed in and check that the trailer
rolls freely. Then, pull out the trailer air supply control. Gently try to pull the tractor
forward to verify the trailer emergency brakes are holding.
10. When you turn suddenly while pulling doubles, which trailer is most likely
to turn over?
The rear trailer is most likely to turn over. It is twice as likely to turn over due to the
"crack-the-whip" effect.
11. When is a trailer most likely to swing around and strike other vehicles?
When it is lightly loaded or empty. An empty trailer has less traction and is more
prone to skidding.
12. When checking trailer height during coupling, what is the correct
procedure?
The trailer should be low enough that it is raised slightly by the tractor when the
tractor backs under it. This ensures proper contact with the fifth wheel.
13. Why should you never drive with the landing gear only part way up?
If left only part way up, it may catch on railroad tracks or other things, causing
serious damage.
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14. What color must the clearance lamps on the front of the vehicle be?
Amber.
15. When backing a large truck, what is the safest practice?
You should have someone guide you to help eliminate blind spots.
16. How many reflectors must every trailer have on the rear?
Two red reflectors.
17. What is the greatest length allowed by state law for any combination truck
or trailer in Texas?
65 feet.
18. What is the youngest age for licensing commercial drivers in Texas?
18 years old. (Note: You must be 21 to drive across state lines).
19. All buses, taxis, and other vehicles hauling passengers for hire must carry a
chemical type fire extinguisher of at least what size?
One quart capacity.
20. How is the number of trailers that may be pulled by one vehicle on the open
highway determined?
By the length limits set by state law.
21. What is the top speed limit for heavy trucks on the open highway in the
daytime in Texas?
60 MPH.
22. When a truck breaks down on a highway in the daytime, what should the
driver set out as warning devices?
Red triangles or two approved red flags.
Texas CDL Section 6 Combination
Vehicles Questions and Correct
Answers
1. What are the two things a driver can do to prevent a rollover?
Keep the cargo as close to the ground as possible to lower the center of gravity, and
drive slowly around turns.
2. Why should you never use the trailer hand valve while driving?
Using it while driving can cause the trailer wheels to skid, which could lead to a
jackknife. You should only use it to test the trailer brakes.
3. What is "off tracking" or "cheating"?
It is when a vehicle goes around a corner and the rear wheels follow a different path
than the front wheels. This is why you must swing wide on turns.
4. Describe what the trailer air supply control does.
When pushed in, it supplies air to the trailer brake system. When pulled out, it shuts
off the air supply and applies the trailer emergency brakes.
5. What is the emergency air line for?
It has two purposes: it supplies air to the trailer air tanks, and it controls the
emergency brakes on combination vehicles.
6. Describe what the service line is for.
The service line (usually blue) carries air, which is controlled by the foot brake or
the trailer hand brake, to apply the service brakes on the trailer.
,2
7. Where are the shut-off valves (cut-out cocks) located?
They are located at the back of trailers, where the air lines connect, and are used
when towing other trailers.
8. How can you test the tractor protection valve?
Charge the system, shut off the engine, and pump the brake pedal to reduce air
pressure. The trailer air supply control should pop out (go into emergency position)
when pressure falls to the manufacturer's specification (usually between 20-45
psi).
9. How do you test the trailer emergency brakes?
Charge the system with the trailer air supply pushed in and check that the trailer
rolls freely. Then, pull out the trailer air supply control. Gently try to pull the tractor
forward to verify the trailer emergency brakes are holding.
10. When you turn suddenly while pulling doubles, which trailer is most likely
to turn over?
The rear trailer is most likely to turn over. It is twice as likely to turn over due to the
"crack-the-whip" effect.
11. When is a trailer most likely to swing around and strike other vehicles?
When it is lightly loaded or empty. An empty trailer has less traction and is more
prone to skidding.
12. When checking trailer height during coupling, what is the correct
procedure?
The trailer should be low enough that it is raised slightly by the tractor when the
tractor backs under it. This ensures proper contact with the fifth wheel.
13. Why should you never drive with the landing gear only part way up?
If left only part way up, it may catch on railroad tracks or other things, causing
serious damage.
, 3
14. What color must the clearance lamps on the front of the vehicle be?
Amber.
15. When backing a large truck, what is the safest practice?
You should have someone guide you to help eliminate blind spots.
16. How many reflectors must every trailer have on the rear?
Two red reflectors.
17. What is the greatest length allowed by state law for any combination truck
or trailer in Texas?
65 feet.
18. What is the youngest age for licensing commercial drivers in Texas?
18 years old. (Note: You must be 21 to drive across state lines).
19. All buses, taxis, and other vehicles hauling passengers for hire must carry a
chemical type fire extinguisher of at least what size?
One quart capacity.
20. How is the number of trailers that may be pulled by one vehicle on the open
highway determined?
By the length limits set by state law.
21. What is the top speed limit for heavy trucks on the open highway in the
daytime in Texas?
60 MPH.
22. When a truck breaks down on a highway in the daytime, what should the
driver set out as warning devices?
Red triangles or two approved red flags.
