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Difficulty: MediumSpace Ahead and Following Distance

A commercial driver is operating a 70-foot combination vehicle at a steady speed of 45 mph on a dry, open highway in clear daylight. According to standard commercial vehicle space management rules, what is the minimum safe following distance the driver should maintain?

  1. A
    4 seconds
  2. B
    7 seconds
  3. 8 secondsAnswer
  4. D
    6 seconds

Answer

8 seconds
Under standard commercial driver licensing guidelines, safe following distance is calculated as 1 second for every 10 feet of vehicle length when traveling at speeds under 40 mph, with 1 additional second added for speeds of 40 mph or greater. For a 70-foot vehicle traveling at 45 mph, the base requirement is 7 seconds plus 1 extra second for highway speed, resulting in a total minimum following distance of 8 seconds.

Step-by-Step Solution

1
Calculate base following distance based on vehicle length
7 seconds
CDL guidelines specify allocating 1 second for every 10 feet of vehicle length (70 feet ÷ 10 = 7 seconds).
2
Apply the speed-dependent modifier
Add 1 second
When operating at speeds of 40 mph or higher, an additional 1 second must be added to provide adequate safety cushion.
3
Sum base interval and speed modifier to determine total following distance
7 seconds + 1 second = 8 seconds
Combining the base length requirement with the highway speed buffer gives the total minimum following distance under good driving conditions.

Key Concept

CDL Following Distance Formula (1 second per 10 feet plus 1 second for speeds 40+ mph)
Estimated Time:1m 0s
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Topics

Space Ahead and Following Distance

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