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. On a tractor or straight truck, at roughly what pressure do the spring brakes come fully on by themselves?

   Correct answer: 20 to 45 psi

   As air pressure falls into about the 20-to-45-psi range, the springs apply the brakes, but you should stop well before that happens.

   Source: Massachusetts CDL Manual — Section 5.1.14: Spring Brakes

2. 2. If one half of a dual air brake system loses most of its pressure while driving, what is the result?

   Correct answer: Either the front or the rear brakes lose full power, so it takes longer to stop

   With one system very low, either the front or rear brakes will not work fully, lengthening your stopping distance; stop safely and get it repaired.

   Source: Massachusetts CDL Manual — Section 5.2: Dual Air Brake Systems

3. 3. After the start-up bulb check, the yellow ABS malfunction lamp stays lit. What does that tell you?

   Correct answer: ABS may no longer be working at one or more of the wheels

   A lamp that stays on after the bulb check, or comes on while driving, warns that one or more wheels may have lost ABS protection.

   Source: Massachusetts CDL Manual — Section 5.1.16: Antilock Braking Systems

4. 4. In the "controlled braking" method for an emergency stop, how do you use the brakes?

   Correct answer: As firmly as possible short of locking the wheels, using only slight steering inputs

   Controlled braking means squeezing the brakes hard but short of lockup, with small steering inputs; release if the wheels lock or you need to steer more.

   Source: Massachusetts CDL Manual — Section 5.4.3: Emergency Stops

5. 5. What is a modulating control valve used for?

   Correct answer: Applying the spring brakes gradually, so you can use them if the service brakes fail

   A modulating valve lets you bring the spring brakes on smoothly by hand, useful as a backup if the service brakes quit.

   Source: Massachusetts CDL Manual — Section 5.1.15: Parking Brake Controls

6. 6. Which sequence describes the "stab braking" method?

   Correct answer: Press the brakes fully, release when the wheels lock, then reapply fully once the wheels start rolling again

   Stab braking is full application, release at lockup, then reapply once the wheels roll; allow up to a second for them to start turning before reapplying.

   Source: Massachusetts CDL Manual — Section 5.4.3: Emergency Stops

7. 7. Some buses have dual parking control valves fed by a small separate air tank. What is that tank for?

   Correct answer: Releasing the spring brakes a limited number of times so the vehicle can be moved during an emergency

   The separate reservoir can release the spring brakes a limited number of times to move the vehicle in an emergency, so plan your moves carefully.

   Source: Massachusetts CDL Manual — Section 5.1.15: Parking Brake Controls

8. 8. As soon as the low-air warning light and buzzer come on, what is the correct action?

   Correct answer: Stop the vehicle somewhere safe immediately, while you still have enough air to control braking

   Do not wait for the spring brakes to grab on their own; stop somewhere safe as soon as the warning appears, while you still have controllable braking.

   Source: Massachusetts CDL Manual — Section 5.1.14: Spring Brakes