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Difficulty: MediumSpace Ahead and Following Distance

You are operating a 4545-foot commercial motorcoach at a cruising speed of 50 mph50\text{ mph} along a dry, multi-lane highway in clear daylight. According to standard commercial vehicle safety guidelines, what is the minimum safe following distance you must maintain behind the vehicle ahead, in seconds?

Answer: 5.5 seconds

Answer

5.5 seconds
The standard commercial driver formula establishes that a driver needs 1 second for each 10 feet of vehicle length at speeds under 40 mph, plus an extra 1 second for speeds of 40 mph or greater. For a 45-foot vehicle traveling at 50 mph, the base requirement is 4.5 seconds (45 ÷ 10) plus 1.0 second for traveling above 40 mph, giving exactly 5.5 seconds.

Step-by-Step Solution

1
Determine the base time interval allocated for vehicle length
4.5 seconds
The commercial driver safety standard requires at least 1 second for each 10 feet of total vehicle length (45 ft ÷ 10 ft/s = 4.5 s).
2
Apply the high-speed safety buffer adjustment
1.0 second addition
When operating at speeds at or above 40 mph, drivers must add 1 additional second to compensate for increased stopping and braking distances.
3
Calculate total required following time gap
5.5 seconds
Summing the base length interval (4.5 seconds) and the speed adjustment (1.0 second) yields the total minimum following buffer of 5.5 seconds.

Key Concept

CDL Following Distance Formula (1 second per 10 feet of vehicle length under 40 mph, plus 1 second for 40 mph and above)
Estimated Time:1m 0s
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Topics

Space Ahead and Following Distance

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