Handling Emergencies

Study questions with answers

8 sample Handling Emergencies questions with the correct answer, a short explanation, and the official handbook reference. Read through them, then take the quiz above.

1. 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. 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. 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. 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. 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. 6. 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)

7. 7. 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

8. 8. When the low-air warning light and buzzer first come on, what is the right response?

   Correct answer: Pull off and stop the vehicle promptly while there is still enough air to control the service brakes.

   Do not wait for the spring brakes to apply on their own; stop safely as soon as the warning activates, while you still have enough air to control the service brakes.

   Source: Section 5.1.14 - Spring Brakes