New York CDL — Air Brakes practice
New York CDL — Air Brakes: Safe Driving Practices practice test
Following distance, scanning, blind spots, using your lights, and the habits that prevent crashes and keep you in control.
Content reviewed against official driver handbooks · August 12, 2026
20 questions · pass with 16 correct. You get instant feedback and an explanation after every answer.
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12 sample Safe Driving Practices questions with the correct answer, a short explanation, and the official handbook reference. Read through them, then take the quiz above.
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1. How is the stop light switch on an air-braked vehicle activated when you brake?
Correct answer: Air pressure operates an electric switch that turns on the brake lights
Air pressure works an electric switch when you put on the air brakes, and that switch turns on the brake lights. This is how drivers behind you are warned that you are slowing.
2. Some air compressors carry a separate oil supply instead of being lubricated by engine oil. What should you do before driving a vehicle with that kind of compressor?
Correct answer: Check the compressor's oil level
A compressor may share the engine's oil or have a supply of its own. When it has its own, that oil level is a pre-drive check, because the compressor is what keeps the air tanks filled.
3. If the air compressor quits working while you are on the road, what do the air storage tanks still let you do?
Correct answer: Use the brakes several more times on the air already stored
The tanks (reservoirs) store enough compressed air for a number of brake applications even with the compressor no longer pumping. How many tanks a vehicle carries, and how large they are, differs from one vehicle to the next.
4. Some air brake systems include an alcohol evaporator. What job does it perform?
Correct answer: It puts alcohol into the system to help keep ice from forming in valves and lines in cold weather
The alcohol evaporator introduces alcohol into the air system to reduce the risk of ice forming in air brake valves and lines during cold weather. Its container should be checked and filled up daily in cold weather.
5. Why do the emergency and parking brakes on trucks, truck tractors and buses have to be held on by mechanical force instead of by air?
Correct answer: Air pressure can leak away over time and cannot be counted on to keep them applied
Air can gradually escape from the system, so brakes that needed air to stay applied could let go. Spring brakes solve this: strong springs apply the brakes whenever the air restraining them is removed, whether the driver exhausts it with the parking control or a leak drains it.
6. As the final step of the seven-step air brake check, how do you test the service brakes before pulling out?
Correct answer: Drive forward at about 5 mph and apply the brake pedal firmly, watching for pulling or delayed stops
Move forward slowly (about 5 mph) and press the brake pedal firmly. Note any pulling to one side, unusual feel, or delayed stopping — these can signal trouble that must be fixed.
7. Why do air tanks with manual drain valves need to be drained at the end of each day of driving?
Correct answer: To remove accumulated water and compressor oil that can harm the brake system
Compressed air carries water, and compressor oil mixes with it inside the tanks. If not drained daily, this water and oil can build up and damage or disable the brakes — and water can freeze in cold weather.
8. A dual air brake system has a "primary" and a "secondary" system that share one set of controls. Which brakes does the primary system usually work?
Correct answer: Usually the rear-axle brakes
The primary system normally supplies the regular brakes at the rear axle or axles, while the secondary system handles the front axle and sometimes one rear axle as well. Each has its own tanks, hoses and lines, and both feed air to a trailer when one is attached.
9. If you are on a downgrade and notice you need increasing application gauge pressure to hold the same speed, what should you conclude?
Correct answer: The brakes are fading and you should slow down and shift to a lower gear
The application pressure gauge shows how much air you are applying to the brakes. Needing more and more pressure to maintain speed means the brakes are fading; slow down and use a lower gear.
10. What information does the supply pressure gauge on the dash give the driver?
Correct answer: How much air pressure is in the air tanks
The supply pressure gauge shows how much air pressure is stored in the air tanks. Vehicles with dual air systems either have two gauges or a single gauge with two needles.
11. Your yellow ABS malfunction lamp stays lit after the start-up bulb check, or it lights up once you are moving. What does that suggest?
Correct answer: ABS control may be lost at one wheel or several
On newer vehicles the lamp lights briefly at start-up to prove the bulb works, then switches off. If it stays on afterward, or lights while you are driving, the antilock function may not be working at one or more wheels. Your regular brakes still work, so drive normally and have the ABS serviced soon.
12. Some older vehicles have a front brake limiting valve with 'normal' and 'slippery' settings. What does the CDL manual say about using it?
Correct answer: Leave it in the 'normal' position, because front-wheel braking works well in all conditions
Research has shown front-wheel braking is good under all conditions, so the manual says to leave the limiting valve in the normal position. The 'slippery' setting cuts front-axle air pressure in half and only reduces stopping power.
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