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
16 questions · pass with 13 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 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. As air is used and tank pressure drops, at approximately what pressure does the governor signal the compressor to begin pumping again?
Correct answer: Around 100 psi
The governor 'cut-in' point is around 100 psi. Between cut-in (about 100 psi) and cut-out (about 125 psi) is the normal operating range.
9. You are testing a combination vehicle: engine off, foot brake fully applied and held. What is the maximum acceptable air pressure drop per minute after the initial drop?
Correct answer: 4 psi per minute
With the brakes applied, leakage must be less than 3 psi per minute for a single vehicle and less than 4 psi per minute for a combination vehicle. More than that indicates a leak that must be repaired before driving.
10. Which type of foundation brake is found on most heavy vehicles equipped with air brakes?
Correct answer: The s-cam drum brake
The s-cam drum brake is the most common foundation brake on air-braked vehicles. Air pressure moves the push rod and slack adjuster, twisting the s-shaped cam that forces the brake shoes against the drum.
11. With a fully charged system, engine off and service brakes released, what is the most air pressure a single vehicle should lose in one minute during a static leakage check?
Correct answer: 2 psi per minute
With the engine off and brakes released, air loss should be less than 2 psi per minute for a single vehicle and less than 3 psi per minute for a combination vehicle. Faster loss means a leak that must be fixed before driving.
12. The governor stops the air compressor from pumping once tank pressure climbs to roughly what level?
Correct answer: About 125 psi
The governor 'cuts out' the compressor at around 125 psi. It cuts the compressor back in when tank pressure falls to about 100 psi.
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