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 vehicle with dual parking control valves and a separate air tank, what limits how you use it to move after the main air is lost?

   Correct answer: The separate tank holds only enough air for a few releases

   The separate reservoir holds only enough air to release the spring brakes a few times, so you must plan your move carefully or risk stopping in a bad spot.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.15 - Parking Brake Controls

2. 2. If the low air pressure warning comes on and pressure keeps falling, why can a heavily loaded vehicle need a long distance to stop?

   Correct answer: Because the spring brakes do not work on all of the axles

   When pressure drops into the 20 to 45 psi range the spring brakes apply, but they do not work on every axle, so a heavy load takes a long distance to stop.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.4.7 - Low Air Pressure

3. 3. What causes brakes to fade from excessive heat?

   Correct answer: Overheating that reduces lining friction and expands the drums

   Overusing the service brakes overheats them; the heat changes the lining chemically to reduce friction and expands the drums so the shoes must reach farther with less force.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.4.5 - Brake Fading or Failure

4. 4. How do spring brakes stay released while you are driving?

   Correct answer: Air pressure holds the springs back until the pressure is removed

   Powerful springs are held back by air pressure during normal driving; if that air is removed or lost, the springs apply the brakes.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.14 - Spring Brakes

5. 5. What is the controlled braking method for an emergency stop?

   Correct answer: Braking as hard as possible without locking the wheels

   In controlled braking you apply the brakes as hard as you can without locking the wheels, keeping steering movements small and releasing if the wheels lock.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.4.3 - Emergency Stops

6. 6. On tractors and straight trucks, spring brakes come fully on when air pressure drops into what range?

   Correct answer: 20 to 45 psi

   Spring brakes typically apply fully once pressure falls to somewhere in the 20 to 45 psi range (often 20 to 30 psi).

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.14 - Spring Brakes

7. 7. What is the purpose of a modulating control valve?

   Correct answer: It lets you apply the spring brakes gradually if the service brakes fail

   A modulating valve lets the driver apply the spring brakes gradually; moving the lever farther applies them harder, which is useful if the service brakes fail.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.15 - Parking Brake Controls

8. 8. Which sequence describes the stab braking method?

   Correct answer: Apply fully, release when the wheels lock, then reapply fully once they roll

   In stab braking you apply the brakes fully, release when the wheels lock, and reapply fully once the wheels start rolling again, allowing time for them to roll.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.4.3 - Emergency Stops