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Difficulty: MediumSpeed and Road Conditions

A commercial combination vehicle is traveling on a two-lane rural highway with a posted speed limit of 60 mph60\text{ mph} when the roadway becomes covered with packed snow. To maintain vehicle control and minimize skid hazards, what is the required maximum speed adjustment and proper retarder setting?

  1. A
    Reduce speed to 40 mph40\text{ mph} and set the engine retarder to its lowest active setting.
  2. B
    Maintain 60 mph60\text{ mph} on straight stretches and brake firmly after entering curves while keeping the retarder engaged.
  3. Reduce speed to 30 mph30\text{ mph} or below and turn off the engine retarder completely.Answer
  4. D
    Reduce speed to 50 mph50\text{ mph} based solely on mechanical braking distance while keeping the retarder active.

Answer

Reduce vehicle speed to 30 mph30\text{ mph} or slower (at least a 50%50\% reduction from the posted speed limit) and turn off the engine retarder completely.
On packed snow, commercial driving regulations require drivers to reduce their road speed by at least one-half (reducing a 60 mph60\text{ mph} speed down to 30 mph30\text{ mph} or slower). In addition, engine retarders must always be switched off on snow, ice, or wet pavement because drive-axle resistance can initiate immediate loss of drive-wheel traction.

Step-by-Step Solution

1
Determine the required speed reduction ratio for packed snow conditions.
On packed snow, CDL safety rules mandate reducing speed by at least one-half (1/21/2). For a 60 mph60\text{ mph} posted limit, the target speed is 602=30 mph\frac{60}{2} = 30\text{ mph} or less.
Packed snow substantially reduces tire-to-road friction, requiring extended stopping distances and lower travel speeds to maintain steering control.
2
Determine the proper operating configuration for engine retarders on slippery surfaces.
Disengage and turn off all auxiliary engine retarders.
Retarders apply mechanical drag strictly to the drive wheels; when traction is poor, this drag can lock drive wheels and cause an immediate jackknife or drive-wheel skid.

Key Concept

Speed reduction guidelines for snow-covered roads and auxiliary retarder safety on slippery surfaces
Estimated Time:1m 0s
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Topics

Speed and Road Conditions

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