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Question

Difficulty: MediumBrake Failure

A commercial driver is descending a steep hill toward a highway interchange when the service brakes experience severe thermal fade and fail to slow the vehicle. Which emergency procedure should the driver execute to safely slow down and regain control of the vehicle?

  1. A
    Rapidly pump the air brake foot valve while remaining in the highest gear to replenish reservoir pressure and restore braking force.
  2. Downshift to a lower gear to utilize engine compression braking, apply the parking brake carefully to avoid wheel lockup, and look for an escape route or ramp.Answer
  3. C
    Immediately place the transmission into neutral and pull the parking brake control valve out fully to instantly lock the drive axles.
  4. D
    Maintain high gear, continuously hold the foot pedal firmly to the floor, and rely on constant friction until the vehicle reaches level ground.

Answer

Downshifting into a lower gear to utilize engine braking, modulating the parking brake without locking the wheels, and seeking an escape route or runaway truck ramp.
When service brakes fade completely on a decline, downshifting harnesses engine compression braking to reduce speed. Controlled application of the parking brake adds stopping force without locking the wheels, and steering toward an escape route or runaway truck ramp provides a safe, controlled stopping area.

Step-by-Step Solution

1
Downshift the transmission into a lower gear.
Engine compression provides vital retarding torque to slow vehicle momentum.
When friction brakes fail due to thermal fade, the powertrain becomes the primary mechanical means of slowing the vehicle.
2
Apply the parking brake or emergency brake system in a controlled manner.
Secondary braking force is applied without abruptly locking the drive wheels.
Sudden wheel lockup will induce an uncontrollable drive-wheel skid or jackknife.
3
Scan ahead and steer toward an escape route, open shoulder, or runaway vehicle ramp.
The vehicle is directed to a designated arresting surface or clear path away from traffic.
Runaway ramps and clear escape paths safely dissipate remaining kinetic energy without colliding with other vehicles.

Key Concept

Emergency response sequence for total service brake failure on downgrades
Estimated Time:1m 0s
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Topics

Brake Failure

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