Georgia CDL — Air Brakes practice
Georgia 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. Which instrument tells you how much air pressure is currently stored in your air tanks?
Correct answer: The supply pressure gauge
Every air-braked vehicle has a supply pressure gauge that shows the pressure available in the air tanks. Vehicles with dual air systems have a gauge (or two gauges) for each half of the system.
2. A safety relief valve on an air tank is normally set to open at about 150 psi. If this valve releases air, what does that tell you?
Correct answer: Something in the system is out of order and needs repair by a mechanic
The safety valve protects the system from too much pressure and should never need to operate under normal conditions. If it releases air, something is wrong — usually the governor or compressor — and the fault should be fixed by a mechanic.
3. How are the brake lights turned on in a vehicle with air brakes?
Correct answer: An electric switch that is operated by air pressure when you brake
Air brake vehicles use a stop light switch that is worked by air pressure. When you put on the brakes, the switch senses the application air and turns on the brake lights.
4. As you use the brakes and tank pressure falls, at about what pressure does the governor put the compressor back to work (cut-in)?
Correct answer: Around 100 psi
When air tank pressure drops to the cut-in level, around 100 psi, the governor allows the compressor to start pumping again to recharge the tanks.
5. During an inspection you pull hard on a push rod attached to a manual slack adjuster (parking brake released, wheels chocked). When does it need adjustment?
Correct answer: If it moves more than about 1 inch where the push rod attaches
With the vehicle on level ground, wheels chocked, and parking brakes released, pull each slack adjuster by hand. If it moves more than about one inch where the push rod attaches, it is out of adjustment and must be fixed.
6. On a downgrade, you notice you must press harder and harder on the pedal to hold your speed, and the application pressure gauge keeps climbing. What does this pattern suggest?
Correct answer: The brakes are fading or are out of adjustment
The application pressure gauge shows how much air you are sending to the brakes. Needing steadily more application pressure to get the same braking means the brakes are fading or out of adjustment — slow down and use a lower gear.
7. In the s-cam drum brake found on most heavy vehicles, what does the s-cam itself actually do?
Correct answer: It turns and pushes the brake shoes apart against the inside of the drum
When the brakes are applied, the push rod moves the slack adjuster, twisting the brake camshaft. The s-shaped cam turns and forces the brake shoes apart, pressing them against the inside of the brake drum.
8. The low air pressure warning signal in an air-braked vehicle must activate before tank pressure falls below:
Correct answer: 55 psi
A warning light, buzzer, or wig wag must come on before air pressure in the tanks drops below 55 psi (or one half the compressor governor cut-out pressure on older vehicles).
9. You are testing a combination vehicle with the brake pedal held fully applied and the engine off. What is the maximum acceptable rate of air loss?
Correct answer: Less than 4 psi per minute
With the brakes applied, air loss must be less than 3 psi per minute for a single vehicle and less than 4 psi per minute for a combination vehicle, measured after the initial pressure drop.
10. In newer air-braked vehicles, the parking brake control is a:
Correct answer: Yellow diamond-shaped knob you pull out to apply
The parking brakes are worked by a yellow, diamond-shaped push-pull knob. Pulling it out applies the parking (spring) brakes; pushing it in releases them.
11. Why do air storage tanks equipped with manual drain valves need to be drained at the end of each day of driving?
Correct answer: To remove water and compressor oil that could harm the brake system
Compressed air carries water and compressor oil into the tanks. If the accumulated water and oil are not drained daily, they can build up and damage or even disable the brakes — and water can freeze in cold weather.
12. Your older tractor has a front brake limiting valve with a "normal" and a "slippery" setting. Current guidance says you should:
Correct answer: Keep the valve in the normal position at all times
The slippery setting cuts the air to the front brakes by half. Testing has shown front wheel braking is good under nearly all conditions, so the manual says to leave the valve in the normal position.
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