Washington CDL — Air Brakes practice
Washington CDL — Air Brakes: Handling Emergencies practice test
What to do when things go wrong — brake failure, tire blowouts, skids, and stalling on railroad tracks.
Content reviewed against official driver handbooks · August 12, 2026
13 questions · pass with 10 correct. You get instant feedback and an explanation after every answer.
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12 sample Handling Emergencies 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. What is the purpose of a modulating control valve for the spring brakes?
Correct answer: To let you apply the spring brakes gradually if the service brakes fail.
A modulating valve is spring-loaded so you can feel the braking and apply the spring brakes gradually, which helps you keep control if the service brakes fail.
Source: Section 5.1.15 - Parking Brake Controls (Modulating valves)
2. On a tractor or straight truck, the spring brakes come fully on when air pressure falls into roughly what range?
Correct answer: 20 to 45 psi.
On a tractor or straight truck the spring brakes set fully once pressure sinks to roughly 20 to 45 psi, commonly 20 to 30; rather than waiting for that, stop safely the moment the low-air warning appears.
Source: Section 5.1.14 - Spring Brakes
3. What does the 'controlled braking' method involve during an emergency stop?
Correct answer: Braking as hard as possible without locking the wheels, keeping steering movements small.
Controlled braking means applying the brakes as hard as you can short of wheel lockup while making only small steering movements; if the wheels lock or you must steer more, release and reapply.
Source: Section 5.4.3 - Emergency Stops (controlled braking)
4. Why can a heavily loaded vehicle need a long distance to stop once the spring brakes apply from low air?
Correct answer: Because the spring brakes do not act on all of the axles.
The spring brakes do not act on every axle, so a heavy vehicle needs a long distance to stop; it is far safer to stop while there is still enough air to use the foot brakes.
Source: Section 5.4.7 - Low Air Pressure
5. When using stab braking, when should you reapply the brakes after releasing them?
Correct answer: Once the wheels begin rolling again, then apply fully.
Stab braking is full application, release when the wheels lock, then reapply fully once they start rolling; it can take up to a second for the wheels to roll again, and reapplying too soon keeps the vehicle from straightening out.
Source: Section 5.4.3 - Emergency Stops (stab braking)
6. How can brakes that are out of adjustment lead to a loss of braking on a long hill?
Correct answer: They stop carrying their share, so the remaining brakes overheat and fade.
Every brake has to carry its share of the work; ones that are out of adjustment quit contributing early, which loads up the properly adjusted brakes until they overheat and fade, leaving too little braking to control the vehicle.
Source: Section 5.4.5 - Brake Fading or Failure
7. Why do some buses have a separate air tank tied to a dual parking control valve?
Correct answer: So the spring brakes can be released briefly to move the vehicle in an emergency.
When main pressure is lost the spring brakes set; a separate tank lets you release them a few times to move the vehicle in an emergency, so plan carefully before that reserve runs out.
Source: Section 5.1.15 - Parking Brake Controls (Dual parking control valves)
8. What most directly causes brake fade on a long grade?
Correct answer: Excessive heat from overusing the service brakes instead of engine braking.
Overusing the service brakes builds excessive heat that changes the lining chemically and expands the drums, cutting friction and contact force; the engine should do the main braking on grades.
Source: Section 5.4.5 - Brake Fading or Failure
9. Air pressure has dropped far enough for the spring brakes to set on an empty rig or on a slippery road. What is the particular danger?
Correct answer: The vehicle may skid and get away from you.
A vehicle with little or no load, or one on a slick surface, can slide out of control when the springs grab; that is one more reason to park while there is still enough air left to brake with the pedal.
Source: Section 5.4.7 - Low Air Pressure
10. The manual gives one exception to braking normally in an emergency. Which vehicle does it apply to?
Correct answer: A straight truck or combination with antilock brakes working on every axle.
Drivers who always operate a straight truck or a combination whose axles all have working antilock brakes are the single exception: in an emergency stop they may push the pedal all the way down.
Source: Section 5.4.2 - Braking with Antilock Brakes
11. In a vehicle without ABS, what happens if you brake hard enough on a slick road to lock the steering wheels?
Correct answer: You lose the ability to steer the vehicle.
Locked steering wheels leave you unable to steer the vehicle; locking the remaining wheels instead invites a skid, a jackknife, or a spin, which is exactly what antilock brakes are meant to prevent.
Source: Section 5.4.2 - Braking with Antilock Brakes
12. You are braking hard in a combination where only the tractor is fitted with ABS, and the trailer starts to swing out. What should you do?
Correct answer: Back off the brakes when it is safe, while watching the trailer.
With ABS on the tractor alone you should still be able to steer and are less likely to jackknife, but keep watching the trailer and ease off the pedal whenever it is safe to do so if the trailer begins to come around.
Source: Section 5.4.2 - Braking with Antilock Brakes
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