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The air brakes endorsement applies to applicants who wish to drive a vehicle with air brakes in Class A, B, or C CDL. To drive a vehicle with air brakes, you must pass the air brake component of the District of Columbia CDL knowledge test. The DC CDL air brakes test consists of 25 questions, and you'll need at least 20 correct answers to pass (80%). The test covers the information found in the air brakes section of the District of Columbia CDL Manual. Take this DC CDL practice test now to prepare for the actual air brakes test!
1. It is not safe to drive a vehicle that has brake drums with cracks that are longer than ___ the width of the friction area.
2. Vehicles with air brakes require more stopping distance than vehicles with hydraulic brakes. Why?
Air brakes use different brake drums.
When driving vehicles with air brakes, the average perception distance increases from 400 feet to 2200 feet.
It takes one half second or more for the air to flow through the lines to the brakes.
Stopping distance for vehicles with air brakes is made up of six different factors.
3. Empty trucks have the best braking. True or False?
It depends on the truck.
It depends on the cargo.
4. If you must stop on a one-way or divided highway, you should place warning devices _______ toward the approaching traffic.
5, 25 and 50 feet
10, 100 and 200 feet
5, 50 and 500 feet
3, 15 and 45 feet
5. Air tanks usually hold enough compressed air to allow the brakes to be used _________ even if the compressor stops working.
for 3 days
for one day
several times
for one stop
6. If your trucks has a high center of gravity, which of the following is true for curves?
You should slow down, as your truck can roll over at the posted speed limit for the curve.
You should travel at the posted speed limit.
Reduce your speed to a crawl.
None of the above.
7. If your brakes fail while you are driving on a downgrade, you should:
use an escape ramp if it's available.
immediately start looking outside your vehicle for something to stop it.
take the least hazardous escape route you can.
All of the above.
8. You should drain the air tanks completely. If water and oil collect in the air tanks:
your brakes could become hard to press.
your brakes could fail.
your brakes could heat up.
None of the above.
9. If the low pressure warning signal doesn't work:
you could lose air pressure and you would know it.
in dual systems the stopping distance will be decreased.
this could cause sudden emergency braking in a single-circuit air system.
None of the above.
10. In vehicles with air brakes, the brake pedal:
let the air out of the spring brakes.
controls the air pressure applied to the brakes.
tells you how much pressure is in the air tanks.
pumps air into the air storage tanks.
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DC CDL Air Brakes Test

Number of questions: 25
Correct answers to pass:20
Passing score:80%
Number of questions: 25
Correct answers to pass:20
Passing score:80%
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