Handling Emergencies

Study questions with answers

10 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. Why does a heavily loaded vehicle need a long distance to stop once the spring brakes come on?

   Correct answer: The spring brakes do not act on all of the axles

   Because the spring brakes do not work on every axle, a heavy load takes a long distance to stop; it is far safer to stop while there is still enough air for the foot brakes.

   Source: Louisiana Commercial Driver's License Manual, Section 5.4.7 - Low Air Pressure

2. 2. On the application pressure gauge, needing more and more pressure to hold the same speed is a sign of what?

   Correct answer: The brakes are fading, so slow down and use a lower gear

   If it takes rising application pressure just to maintain speed, the brakes are fading; the response is to slow down and shift to a lower gear.

   Source: Louisiana Commercial Driver's License Manual, Section 5.1.10 - Application Pressure Gauge

3. 3. What should you do when the low air pressure warning first comes on?

   Correct answer: Stop the vehicle safely without delay, while you still have enough air to control it

   Do not wait for the spring brakes to grab on their own; stop safely as soon as the warning appears, while you still have control of the brakes.

   Source: Louisiana Commercial Driver's License Manual, Section 5.1.14 - Spring Brakes

4. 4. What does 'controlled braking' mean during an emergency stop?

   Correct answer: Braking as firmly as possible just short of a wheel lockup, using only small steering inputs

   Controlled braking means braking hard but short of lockup while keeping steering inputs small; if the wheels lock or you must steer more, release and re-apply.

   Source: Louisiana Commercial Driver's License Manual, Section 5.4.3 - Emergency Stops

5. 5. On a tractor or straight truck, the spring brakes come fully on when air pressure drops into what range?

   Correct answer: 20 to 45 psi

   Spring brakes on tractors and straight trucks apply fully once pressure falls to the 20-to-45 psi range, often 20 to 30 psi.

   Source: Louisiana Commercial Driver's License Manual, Section 5.1.14 - Spring Brakes

6. 6. What does it mean if the safety valve lets air escape?

   Correct answer: Something is wrong and a mechanic should repair it

   The safety valve venting air is a sign of a fault in the system, and it should be repaired by a mechanic.

   Source: Louisiana Commercial Driver's License Manual, Section 5.1.6 - Safety Valve

7. 7. If the ABS malfunction lamp stays on after the bulb check or comes on while driving, what does it likely mean?

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

   A lamp that stays lit after start-up or turns on while under way means ABS may have quit at one or more wheels.

   Source: Louisiana Commercial Driver's License Manual, Section 5.1.16 - Antilock Braking Systems (ABS)

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

   Correct answer: Fully applying the brakes, releasing when the wheels lock, then reapplying fully once they roll again

   In stab braking you press the brakes all the way, release when the wheels lock, and fully apply again once the wheels begin rolling.

   Source: Louisiana Commercial Driver's License Manual, Section 5.4.3 - Emergency Stops

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

   Correct answer: To let the driver apply the spring brakes gradually if the service brakes fail

   The spring-loaded modulating valve lets you apply the spring brakes little by little, giving you control if the service brakes quit.

   Source: Louisiana Commercial Driver's License Manual, Section 5.1.15 - Parking Brake Controls

10. 10. What is the main cause of brake fade?

    Correct answer: Excessive heat from overusing the brakes instead of using engine braking

    Overusing the service brakes, instead of relying on engine braking, overheats them; the heat changes the lining and expands the drums, reducing braking.

    Source: Louisiana Commercial Driver's License Manual, Section 5.4.5 - Brake Fading or Failure