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Question

Difficulty: EasySpace Ahead and Following Distance

While driving a 40-foot intercity passenger bus at a steady cruising speed of 45 mph on a clear, dry roadway, how many seconds of following distance must you maintain behind the lead vehicle to satisfy CDL safety standards?

  1. A
    3 seconds
  2. B
    4 seconds
  3. 5 secondsAnswer
  4. D
    1.5 seconds

Answer

5 seconds
According to the CDL manual, drivers must maintain at least 1 second of following distance for every 10 feet of vehicle length under ideal conditions, plus an additional 1 second when traveling at 40 mph or faster. For a 40-foot vehicle traveling at 45 mph, the calculation is 4 seconds (for vehicle length) + 1 second (for speed over 40 mph) = 5 seconds.

Step-by-Step Solution

1
Calculate base following distance for vehicle length
4 seconds
The standard rule specifies 1 second for every 10 feet of vehicle length (40 ft÷10 ft/sec=4 seconds40\text{ ft} \div 10\text{ ft/sec} = 4\text{ seconds}).
2
Evaluate operating speed adjustment
Add 1 second
Speeds of 40 mph or higher require adding 1 extra second to compensate for increased braking distance.
3
Sum the total required time interval
5 seconds (4+1=54 + 1 = 5)
Total safe following distance equals length allowance plus high-speed modifier.

Key Concept

Commercial vehicle following distance calculation using the 1 second per 10 feet plus speed modifier rule
Estimated Time:45s
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Topics

Space Ahead and Following Distance

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