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Question

Difficulty: EasyMountain Driving and Steep Downgrades

When descending a steep mountain downgrade on wet pavement during rainy weather, how should you operate your vehicle's engine retarder?

  1. A
    Keep the retarder set to maximum power to minimize wear on the service brakes.
  2. Turn off the retarder to prevent the drive wheels from skidding.Answer
  3. C
    Apply light, continuous pressure to the brake pedal while running the retarder.
  4. D
    Downshift through multiple gears while rolling down the hill to boost retarder efficiency.

Answer

Turn off the retarder to prevent the drive wheels from skidding.
Engine retarders apply braking resistance directly to the drive axles. On slippery or wet surfaces, this retarding force can easily exceed tire traction, causing the drive wheels to lock and initiating a drive-wheel skid or jackknife. CDL safety rules mandate turning retarders off whenever road conditions are wet, snowy, or icy.

Step-by-Step Solution

1
Identify the prevailing road surface condition.
The roadway is wet and traction between tires and pavement is significantly reduced.
Surface traction dictates whether auxiliary deceleration systems can be safely utilized.
2
Analyze how engine retarders interact with low-traction surfaces.
Retarders apply braking force specifically to the drive wheels, which can quickly overcome reduced tire grip.
When drive wheels lock up or lose traction while the rest of the combination rolls freely, a drive-wheel skid or jackknife occurs.
3
Select the proper operational safety procedure.
Disengage the retarder completely whenever the road is wet, icy, or snow-covered.
Turning off the retarder ensures directional stability and allows the driver to rely on proper low gear selection and snub braking.

Key Concept

Engine retarders must be turned off when roads are wet, icy, or snow-covered because their focused braking force on drive axles can cause wheel lockup and skidding.
Estimated Time:45s
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Topics

Mountain Driving and Steep Downgrades

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