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Difficulty: MediumSpeed Control and Following Distance

A motorist is driving on a two-lane highway at 40 mph40\text{ mph} directly behind a large commercial truck during light rainfall. Given the damp pavement and restricted view of the road ahead, which following distance should the driver maintain?

  1. At least 4 seconds, to allow extra stopping distance on slippery pavement and compensate for reduced visibility.Answer
  2. B
    The standard 3-second distance, because traveling at or below 40 mph40\text{ mph} automatically ensures sufficient braking time regardless of weather.
  3. C
    A reduced 2-second distance, as long as the driver maintains focus directly on the truck's brake lights.
  4. D
    Exactly 1 car length for every 10 mph10\text{ mph} of speed, regardless of weather or road surface conditions.

Answer

The driver should maintain a following distance of at least 4 seconds to account for reduced traction on wet pavement and limited vision around the large vehicle.
Under normal, dry conditions, a minimum following distance of 3 seconds is recommended. However, when driving on wet pavement or behind large vehicles that block the view ahead, drivers must increase their following distance to at least 4 seconds to compensate for longer braking distances and reduced reaction time.

Step-by-Step Solution

1
Identify the standard baseline following distance under ideal conditions.
The standard minimum following distance under clear, dry conditions is 3 seconds.
Establishing a baseline space cushion allows drivers time to perceive and react to hazards.
2
Evaluate the environmental and traffic factors in the scenario.
Light rain creates slippery road surfaces, and following a large truck obscures forward sight lines.
Wet pavement reduces tire traction, increasing braking distance, while large vehicles prevent visual scanning ahead.
3
Adjust the following distance to maintain safe operations.
Increase the following distance from 3 seconds to at least 4 seconds.
Adding an extra second or more creates a sufficient safety buffer to stop safely if the lead vehicle brakes suddenly.

Key Concept

Adjusting Following Distance for Adverse Conditions and Large Vehicles
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Topics

Speed Control and Following Distance

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