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Difficulty: HardNight Driving

An operator drives an articulated tractor-trailer along a dark, rural corridor using low-beam headlights that illuminate approximately 250 feet250\text{ feet} ahead. The vehicle travels at 55 mph55\text{ mph}, where total stopping distance—accounting for perception, reaction, and heavy-vehicle braking—is roughly 300 feet300\text{ feet}. If an unlit stationary obstacle appears at the farthest edge of the headlight beam, which outcome will occur if maximum braking is initiated immediately upon perception?

  1. A
    The truck will stop just before the obstacle because braking distance alone on dry pavement at 55 mph55\text{ mph} is less than 250 feet250\text{ feet}.
  2. B
    The truck will stop safely because nighttime reaction distance decreases when focused on illuminated pavement markers.
  3. The truck will strike the obstacle because the total stopping distance exceeds the illuminated sight distance of the low beams.Answer
  4. D
    The truck will safely clear the obstacle because high-beam residual light extends driver perception beyond the low-beam illumination limit.

Answer

The truck will strike the obstacle because the total stopping distance exceeds the illuminated sight distance of the low beams.
Traveling at a speed where total stopping distance (300 feet300\text{ feet}) exceeds headlight visibility range (250 feet250\text{ feet}) is known as overdriving headlights. When an unlit obstacle appears at the limit of low-beam visibility, the vehicle requires 300 feet300\text{ feet} to stop and will inevitably strike the obstacle located 250 feet250\text{ feet} away.

Step-by-Step Solution

1
Determine the available sight distance
Low-beam headlights illuminate roughly 250 feet250\text{ feet} ahead.
Sight distance represents the maximum forward distance in which a driver can perceive a hazard.
2
Determine the required total stopping distance
Total stopping distance at 55 mph55\text{ mph} is approximately 300 feet300\text{ feet} (perception distance + reaction distance + braking distance).
Safe vehicle operation requires stopping completely within the illuminated visual range.
3
Compare total stopping distance with illuminated sight distance
300 feet>250 feet300\text{ feet} > 250\text{ feet}, confirming the driver is overdriving the headlights.
Because the vehicle requires 300 feet300\text{ feet} to stop but the obstacle is first detected at 250 feet250\text{ feet}, the vehicle will travel past the obstacle location before coming to a stop.

Key Concept

Overdriving Headlights and Total Stopping Distance at Night
Estimated Time:1m 30s
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Topics

Night Driving

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