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Difficulty: EasySpace Ahead and Following Distance

A professional driver is operating a 2020-foot straight delivery truck at 25 mph25\text{ mph} in clear weather on a dry downtown street. According to commercial driving safety standards, what is the minimum safe following distance the driver should maintain behind the vehicle ahead?

  1. A
    1 second1\text{ second}
  2. 2 seconds2\text{ seconds}Answer
  3. C
    3 seconds3\text{ seconds}
  4. D
    4 seconds4\text{ seconds}

Answer

2 seconds2\text{ seconds}
Under normal driving conditions at speeds below 40 mph40\text{ mph}, the standard CDL following distance formula requires 1 second1\text{ second} for every 10 feet10\text{ feet} of vehicle length. For a 2020-foot straight truck traveling at 25 mph25\text{ mph}, the required safe interval is 20/10=2 seconds20 / 10 = 2\text{ seconds}.

Step-by-Step Solution

1
Apply the baseline commercial vehicle following distance formula: allow 1 second1\text{ second} for each 10 feet10\text{ feet} of vehicle length.
20 feet10 feet=2 seconds\frac{20\text{ feet}}{10\text{ feet}} = 2\text{ seconds}
This establishes the base time cushion needed to perceive hazards and begin braking.
2
Check whether the operating speed requires the high-speed safety adjustment.
The truck is traveling at 25 mph25\text{ mph}, which is below 40 mph40\text{ mph}, so no extra second is added.
An additional 1 second1\text{ second} is only required when driving at speeds of 40 mph40\text{ mph} or above.

Key Concept

Calculating safe following distance using the 1 second per 10 feet rule for speeds below 40 mph
Estimated Time:45s
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Topics

Space Ahead and Following Distance

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