Texas CDL — Air Brakes practice
Texas CDL — Air Brakes: Speed & Space Management practice test
Choosing a safe speed, keeping a space cushion, adjusting for weather and traffic, and understanding stopping distance.
Content reviewed against official driver handbooks · August 12, 2026
10 questions · pass with 8 correct. You get instant feedback and an explanation after every answer.
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Study questions with answers
10 sample Speed & Space Management 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 list correctly names all the parts of total stopping distance for a vehicle with air brakes?
Correct answer: Perception + reaction + brake lag + effective braking distance
Total stopping distance with air brakes equals perception distance plus reaction distance plus brake lag distance plus effective braking distance. The brake lag component is what hydraulic-braked vehicles do not have.
2. For an average driver in an air-braked vehicle at 55 mph, with good traction and brakes, the total stopping distance is about how far?
Correct answer: More than 450 feet
Add perception, reaction, brake lag, and braking distance together and the total at 55 mph comes to more than 450 feet under good conditions. Brake lag alone contributes roughly 32 feet of that.
3. What is "controlled braking" in an emergency stop?
Correct answer: Braking as hard as possible without locking the wheels
Controlled braking means applying the brakes as hard as you can without locking the wheels, keeping steering movements very small while you do it. Locked wheels mean lost steering control.
4. For a normal stop in a vehicle with air brakes and a manual transmission, how should you use the brake pedal?
Correct answer: Brake smoothly to a safe stop, clutching only near idle rpm
Push the pedal down until the vehicle slows with a safe, smooth stop, and do not push the clutch in until the engine rpm is close to idle. If you have a manual transmission, be in a gear that lets you start moving again once stopped.
5. At 55 mph, roughly how much extra stopping distance does brake lag alone add for an air-braked vehicle?
Correct answer: About 32 feet
At 55 mph, the 0.4-second brake lag adds about 32 feet of travel before the brakes even begin to work. That distance is on top of perception, reaction, and effective braking distance.
6. You are stab braking in an emergency. After the wheels lock and you release the pedal, when do you apply the brakes fully again?
Correct answer: As soon as the wheels start rolling again
In stab braking, you apply the brakes all the way, release when the wheels lock up, and reapply fully as soon as the wheels start rolling again. It can take up to a second for the wheels to start rolling after release.
7. How does having antilock brakes affect the stopping distance of an air-braked truck?
Correct answer: It may not shorten the stop, but it helps you keep control during hard braking
ABS steps in only when wheels are close to locking and does not raise or lower your normal braking power. Your stop might not be any shorter, yet you keep the ability to steer around an obstacle and avoid skids from braking too hard, so leave the same following distance.
8. Unlike hydraulic brakes, air brakes have brake lag. About how long does it take air to flow through the lines and work the brakes after you press the pedal?
Correct answer: One half second or more
Air needs time to travel through the lines before the brakes work: one half second or more after you push the pedal. This brake lag adds roughly 32 feet of stopping distance at 55 mph on dry pavement.
9. Before starting down a long, steep grade in an air-braked vehicle, when should you shift into the proper low gear?
Correct answer: Before you start down the grade
You must be in the proper low gear before starting down the hill, so engine braking can hold the vehicle back and the service brakes are saved for snubbing. Trying to downshift after speed builds may be impossible.
10. Why does an air-braked vehicle need a greater following distance than a car traveling the same speed?
Correct answer: Brake lag adds stopping distance that hydraulic brakes do not have
Air brakes add brake lag distance — the time air needs to flow through the lines — on top of perception, reaction, and braking distance. A heavy vehicle also simply takes longer to slow.
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