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Difficulty: MediumDriving in Fog

While navigating a multi-lane bypass, a commercial driver enters an area of thick ground fog that severely restricts visibility and leaves a thin layer of moisture across the roadway. Which action should the driver take to maintain safe vehicle control and prevent a collision?

  1. A
    Keep auxiliary engine retarders set to maximum braking capacity to control vehicle speed without heating the service brakes on damp pavement.
  2. Disengage auxiliary engine retarders, switch headlights to low beam, and adjust speed so the vehicle can stop within the visible distance ahead.Answer
  3. C
    Decrease following distance behind a leading commercial vehicle to use its taillights as a visual navigation guide through the dense fog.
  4. D
    Switch to high-beam headlights and maintain cruising speed under the assumption that emergency braking distance alone dictates total stopping distance.

Answer

Disengage auxiliary engine retarders, switch headlights to low beam, and adjust speed so the vehicle can stop within the visible distance ahead.
In dense fog, atmospheric condensation coats asphalt, creating slippery conditions that necessitate turning off auxiliary engine retarders to avoid drive-wheel skidding. Headlights must be kept on low beam to minimize blinding reflection from water droplets, and vehicle speed must be reduced so total stopping distance remains well within the forward sight distance.

Step-by-Step Solution

1
Assess traction and lighting hazards caused by atmospheric condensation and fog.
Identify that fog leaves pavement slick and creates high back-reflection against high beams.
Condensation reduces tire traction, and airborne water droplets scatter bright light directly back into the driver's eyes.
2
Select proper vehicle controls and lighting configurations.
Turn off engine retarders and ensure headlights are set to low beam.
Retarders applied to slippery drive wheels cause skids and jackknifes, whereas low beams direct light down toward the pavement.
3
Calibrate driving speed based on sight distance and total stopping distance components.
Slow down sufficiently so total stopping distance (perception + reaction + braking) does not exceed clear sight distance.
If an unlit stalled vehicle or road hazard appears, the driver must be able to come to a complete stop before reaching it.

Key Concept

Defensive speed adjustment, proper headlight selection, and retarder disengagement during fog operations
Estimated Time:1m 0s
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Topics

Driving in Fog

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