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Difficulty: MediumNight Driving

A commercial motor vehicle driver is operating on an unlit two-lane highway at night with low-beam headlights in use. To ensure the vehicle can safely stop before encountering an unseen hazard in the roadway, which operating rule must the driver follow?

  1. A
    Maintain a speed that allows only the vehicle's mechanical braking distance to fit within the illuminated area, excluding driver reaction time.
  2. Adjust travel speed so that total stopping distance, including perception, reaction, and braking distances, does not exceed the distance illuminated by the headlights.Answer
  3. C
    Continue at the posted daytime speed limit while using a fixed two-second following interval relative to the headlight beam cutoff point.
  4. D
    Operate at normal highway cruising speed and rely on rapid evasive steering rather than speed reduction to avoid obstacles detected inside the beam boundary.

Answer

Adjust travel speed so that total stopping distance, including perception, reaction, and braking distances, does not exceed the distance illuminated by the headlights.
According to the official CDL manual, a driver must never overdrive their headlights. Total stopping distance is made up of perception distance, reaction distance, brake lag distance, and effective braking distance. If a vehicle travels at a speed where the total stopping distance exceeds the forward distance illuminated by the headlights, the driver will not be able to stop before striking an unexpected hazard.

Step-by-Step Solution

1
Identify the limiting visibility factor during night driving operations.
Headlights illuminate only a specific distance ahead (typically 250 feet for low beams and 350 to 500 feet for high beams).
Drivers can only react to hazards they can clearly see within their illuminated field of vision.
2
Calculate the relationship between vehicle speed and total stopping distance components.
Total stopping distance consists of perception distance, reaction distance, brake lag distance, and effective braking distance.
If total stopping distance exceeds the illuminated distance, the driver is overdriving the headlights and will collide with any stationary hazard before being able to stop.
3
Select the correct speed management principle for nighttime safety.
The driver must adjust vehicle speed so the total distance required to come to a full stop remains within the distance illuminated by the headlights.
This guarantees adequate space to detect, react, and stop safely prior to reaching an unexpected obstacle.

Key Concept

Preventing overdriving headlights by keeping total stopping distance within headlight sight range
Estimated Time:1m 0s
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Topics

Night Driving

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