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Question

Difficulty: MediumWinter Driving

A tractor-trailer enters a divided highway section where falling temperatures have turned accumulated precipitation into hard-packed snow. Under official commercial driver safety standards, which speed adjustment and vehicle control action must the driver execute?

  1. A
    Reduce speed by one-third and place the engine retarder on its highest setting to ease the load on the service brakes.
  2. B
    Maintain normal highway travel speed while observing the standard dry-road following distance guideline of one second per ten feet of vehicle length.
  3. Reduce speed by at least half and ensure the engine retarder is turned off.Answer
  4. D
    Maintain cruising speed while riding the service brake pedal lightly to keep the drums warm and free of slush.

Answer

Reduce vehicle speed by at least half and ensure the engine retarder is turned off.
According to official CDL safety standards, drivers must reduce their speed by at least half on packed snow (compared to one-third on wet pavement, and slowing to a crawl on ice). Furthermore, engine retarders must always be switched off whenever road surfaces are slippery (wet, snow-covered, or icy) because their auxiliary braking force applies only to drive axles and can cause drive wheels to lock up, resulting in a sudden spin or jackknife.

Step-by-Step Solution

1
Determine the required speed adjustment for hard-packed snow.
Identify that safe operating guidelines require a speed reduction of at least 50% (by half) or more on packed snow compared to dry roads.
Packed snow substantially degrades tire-to-surface coefficient of friction, greatly extending total stopping distance.
2
Evaluate auxiliary braking and engine retarder status for slippery winter surfaces.
Deactivate all engine retarders (Jake brakes, driveline retarders, exhaust brakes).
Retarder braking force is applied exclusively to the drive wheels without service brake application; on slippery surfaces, this concentrated drag can cause drive wheels to lose grip and provoke an immediate jackknife.

Key Concept

Speed reduction guidelines and retarder deactivation on packed snow
Estimated Time:1m 0s
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Topics

Winter Driving

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