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Difficulty: Very hardStopping and Braking Procedures

While preparing to navigate a 6-mile-long, 7% downgrade, an operator of a fully loaded tractor-trailer observes that the road surface is covered with packed snow. The driver determines that the maximum safe operating speed for these adverse conditions is 25 mph. The vehicle is equipped with an engine retarder. To safely manage the descent and maintain total vehicle control, which sequence of braking and speed management procedures must the driver execute?

  1. Deactivate the engine retarder completely, engage a low gear before beginning the descent, apply the service brakes to reduce the speed from 25 mph to 20 mph, and then release the brakes entirely until the vehicle reaches 25 mph again.Answer
  2. B
    Keep the engine retarder engaged on its lowest setting to prevent brake fade, and utilize the stab braking method by fully locking and releasing the brakes whenever the vehicle exceeds 25 mph.
  3. C
    Turn off the engine retarder, select the appropriate downhill gear, and apply a continuous, light pressure on the service brake pedal to hold the vehicle steadily at exactly 25 mph throughout the grade.
  4. D
    Deactivate the engine retarder, maintain normal highway speed at the crest of the hill, and apply firm, continuous braking only when approaching the steepest sections or sharp curves to reach the 25 mph safe speed.

Answer

The correct sequence is to deactivate the engine retarder completely, select a low gear prior to the descent, and use the snub braking technique (applying brakes from 25 mph down to 20 mph, then releasing).
The correct response successfully synthesizes three critical rules for descending a grade in adverse weather: First, engine retarders must be turned off on slippery roads to prevent drive-wheel skids. Second, the vehicle must be in the proper low gear before starting the descent. Third, the driver must employ proper snub braking, which dictates applying the brakes to reach 5 mph below the designated safe speed, then releasing them fully to allow the components to cool.

Step-by-Step Solution

1
Evaluate the road conditions and retarder usage.
Because the road is covered in packed snow, the engine retarder must be turned off completely.
Engine retarders apply braking force only to the drive wheels, which can quickly cause a loss of traction and a drive-wheel skid on slippery surfaces.
2
Determine the proper gearing strategy.
The driver must select a gear low enough to hold the vehicle back before beginning the descent.
Attempting to downshift while already descending a steep grade can result in getting stuck in neutral and losing all engine braking capability.
3
Apply the correct downhill braking technique (snubbing).
Brake from the safe speed of 25 mph down to 20 mph, release the brakes completely, and repeat when the vehicle reaches 25 mph again.
Snubbing allows the brake drums and linings to cool during the release phase, preventing heat buildup, brake fade, and potential catastrophic failure.

Key Concept

Downhill Speed Management and Snub Braking Procedures
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Topics

Stopping and Braking Procedures

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