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Difficulty: MediumNight Driving

Total stopping distance for a commercial motor vehicle is the sum of perception distance, reaction distance, and brake lag plus effective braking distance. When operating on an unlit roadway at night, which rule must a driver follow to avoid overdriving the headlights?

  1. A
    Maintain the standard daytime following interval without reducing travel speed for restricted visibility distance.
  2. Adjust travel speed so the vehicle's total stopping distance does not exceed the distance illuminated by the headlights.Answer
  3. C
    Base travel speed solely on mechanical braking distance while omitting perception and reaction distances from the sight calculation.
  4. D
    Continue at the posted daytime speed limit under the assumption that high beams can be switched on instantly if a hazard appears.

Answer

Adjust travel speed so the vehicle's total stopping distance does not exceed the distance illuminated by the headlights.
The correct answer emphasizes that total stopping distance must never exceed the distance illuminated by the headlights. If a commercial vehicle is traveling at a speed requiring 300 feet to stop but low beams illuminate only 250 feet ahead, an obstacle spotted at the edge of the light will be struck before the vehicle can stop.

Step-by-Step Solution

1
Identify the limiting factor of night driving visibility.
Headlights provide limited forward illumination (typically 250 feet for low beams and 350 to 500 feet for high beams).
A driver cannot react to or brake for a hazard that has not yet entered the illuminated zone.
2
Apply the definition of total stopping distance to night driving constraints.
Total stopping distance includes perception distance, reaction distance, and braking distance.
The entire stopping process must occur within the visible range to prevent colliding with an obstacle.
3
Determine the necessary operational speed adjustment.
Vehicle speed must be reduced to a level where the full stopping distance fits entirely inside the illuminated sight distance.
Driving faster than the speed that allows stopping within headlight reach is known as overdriving headlights and leads to unavoidable collisions.

Key Concept

Headlight sight distance and total stopping distance alignment during night operations
Estimated Time:1m 0s
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Topics

Night Driving

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