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Difficulty: HardSpace Ahead and Following Distance

A commercial driver is operating a 6565-foot specialized automobile transporter along a two-lane rural highway at a steady cruising speed of 48 mph48\text{ mph} under ideal weather and dry pavement conditions. According to the standard CDL following distance formula, which requires 1 second1\text{ second} for every 10 feet10\text{ feet} of vehicle length at speeds under 40 mph40\text{ mph} plus an additional 1 second1\text{ second} for speeds at or above 40 mph40\text{ mph}, what is the minimum required following distance, in seconds, that the driver must maintain behind the vehicle ahead?

Answer: 7.5 seconds

Answer

7.5 seconds
The standard commercial driver following distance formula mandates allocating 1 second for every 10 feet of vehicle length for speeds under 40 mph, plus an additional 1 second for operating speeds at or above 40 mph. For a 65-foot combination vehicle, the baseline interval is 65 / 10 = 6.5 seconds. Because the vehicle is traveling at 48 mph (which meets or exceeds 40 mph), 1 additional second must be added, resulting in a total required following distance of 6.5 + 1.0 = 7.5 seconds.

Step-by-Step Solution

1
Calculate the base space requirement for the vehicle's bumper-to-bumper length.
65 feet / 10 feet per second = 6.5 seconds.
Commercial driver safety standards require a baseline of 1 second of following distance for every 10 feet of overall vehicle length.
2
Evaluate the operating speed and determine if an additional buffer is required.
Add 1.0 second because 48 mph is greater than or equal to 40 mph.
At speeds at or above 40 mph, stopping distance significantly increases due to longer braking distances, requiring an extra second of safety cushion.
3
Sum the baseline time and the high-speed safety modifier to obtain total following distance.
6.5 seconds + 1.0 second = 7.5 seconds.
Combining the length-based interval with the speed adjustment provides the total minimum safe following time under ideal conditions.

Key Concept

CDL Following Distance Rule (1 second per 10 feet of vehicle length + 1 second for speeds >= 40 mph)
Estimated Time:1m 30s
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Topics

Space Ahead and Following Distance

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