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Difficulty: MediumNight Driving

A tractor-trailer travels on an unlit highway where low-beam headlights illuminate objects up to 250 feet250\text{ feet} ahead. At a speed of 55 mph55\text{ mph}, the truck requires approximately 419 feet419\text{ feet} of total stopping distance, which includes perception, reaction, and braking distances combined. Which action is required to ensure the driver can safely stop for an unexpected hazard in the lane ahead?

  1. A
    Maintain 55 mph55\text{ mph} while calculating stopping capability based solely on braking distance and omitting perception and reaction distances.
  2. Reduce traveling speed so that the vehicle's total stopping distance does not exceed the 250-foot250\text{-foot} illuminated sight range.Answer
  3. C
    Continue driving at 55 mph55\text{ mph} under the assumption that low-beam illumination provides adequate warning at highway cruising speeds.
  4. D
    Rely exclusively on a four-second following distance without reducing speed to compensate for low-beam visibility limits.

Answer

Reduce traveling speed so that the vehicle's total stopping distance does not exceed the 250-foot250\text{-foot} illuminated sight range.
At night, a commercial driver must never overdrive the headlights. Total stopping distance consists of perception distance, reaction distance, and braking distance. When low-beam headlights only illuminate 250 feet250\text{ feet} ahead, operating at a speed that requires 419 feet419\text{ feet} to stop means the vehicle cannot stop in time if a hazard appears in the headlights. The driver must reduce vehicle speed until total stopping distance is within the illuminated distance.

Step-by-Step Solution

1
Compare the vehicle's total stopping distance at the current speed with the headlight illumination distance.
At 55 mph55\text{ mph}, total stopping distance is 419 feet419\text{ feet}, which is 169 feet169\text{ feet} greater than the 250-foot250\text{-foot} low-beam sight range.
This condition constitutes overdriving the headlights, meaning a hazard will be reached before the vehicle can physically stop.
2
Determine the necessary defensive driving adjustment per commercial driving standards.
The driver must decrease speed until total stopping distance (perception + reaction + braking) falls within the 250-foot250\text{-foot} illuminated field.
Commercial motor vehicle operators must always be able to stop within the distance they can see ahead.

Key Concept

Headlight Sight Range and Overdriving Headlights
Estimated Time:1m 0s
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Topics

Night Driving

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