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Difficulty: MediumSpace Ahead and Following Distance

A driver is navigating a 40-foot40\text{-foot} motor coach along an expressway bypass at a steady cruising speed of 45 mph45\text{ mph} during clear, dry weather. To maintain a safe space cushion ahead, what is the minimum following interval the driver should maintain behind the vehicle in front?

  1. A
    A minimum gap of 4 seconds4\text{ seconds}
  2. A minimum gap of 5 seconds5\text{ seconds}Answer
  3. C
    A minimum gap of 8 seconds8\text{ seconds}
  4. D
    A minimum gap of 2.5 seconds2.5\text{ seconds}

Answer

A minimum gap of 5 seconds5\text{ seconds}
Under CDL space management guidelines, drivers must allow 1 second for every 10 feet of vehicle length when driving under 40 mph, and add 1 additional second for speeds of 40 mph or greater. For a 40-foot vehicle traveling at 45 mph, the calculation is 4 seconds for length plus 1 second for speed, equaling 5 seconds of following distance.

Step-by-Step Solution

1
Calculate the base following distance based on vehicle length.
40 feet10 feet/second=4 seconds\frac{40\text{ feet}}{10\text{ feet/second}} = 4\text{ seconds}
Commercial driver standards mandate allocating 1 second for every 10 feet of vehicle length.
2
Apply the speed-based adjustment factor.
Add 1 second1\text{ second} because 45 mph≥40 mph45\text{ mph} \geq 40\text{ mph}.
At speeds of 40 mph or greater, an additional 1 second must be added to provide sufficient stopping space.
3
Sum the base following time and speed adjustment.
4 seconds+1 second=5 seconds4\text{ seconds} + 1\text{ second} = 5\text{ seconds}
The total following distance represents the minimum safe space cushion ahead under ideal conditions.

Key Concept

The CDL following distance formula requires 1 second per 10 feet of vehicle length at speeds below 40 mph, plus 1 additional second at speeds of 40 mph and above.
Estimated Time:1m 0s
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Topics

Space Ahead and Following Distance

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