An automobile transporter with an overall length of 85\text{ feet} is cruising at a steady… — Commercial Driver's License (CDL) General Knowledge Exam

An automobile transporter with an overall length of $85\text{ feet}$ is cruising at a steady speed of $48\text{ mph}$ on a clear, dry interstate highway. Under standard commercial motor vehicle safety regulations, what is the minimum safe following distance the driver should maintain behind the vehicle ahead?

A
$8.5\text{ seconds}$
B
$4.8\text{ seconds}$
$9.5\text{ seconds}$ Answer
D
$10.5\text{ seconds}$

Answer

The minimum safe following distance is

9.5\text{ seconds}

The correct answer provides a following cushion of

9.5\text{ seconds}

. According to the CDL manual, a driver must maintain at least

1\text{ second}

of space for each

10\text{ feet}

of vehicle length (

85\text{ ft} / 10 = 8.5\text{ s}

). When traveling at

40\text{ mph}

or higher, an additional

1\text{ second}

must be added (

8.5\text{ s} + 1.0\text{ s} = 9.5\text{ s}

Step-by-Step Solution

Calculate the base following distance based on vehicle length.

\frac{85\text{ feet}}{10\text{ feet/second}} = 8.5\text{ seconds}

Commercial driver regulations require allowing at least

1\text{ second}

for each

10\text{ feet}

of vehicle length.

Evaluate the operating speed and apply the speed modifier.

48\text{ mph} \ge 40\text{ mph} \implies +1.0\text{ second}

When operating at speeds of

40\text{ mph}

or greater, drivers must add

1\text{ second}

to their total following cushion to account for increased stopping distance.

Compute the total minimum required following time.

8.5\text{ seconds} + 1.0\text{ second} = 9.5\text{ seconds}

Summing the vehicle length requirement and the high-speed safety buffer yields the total minimum following distance.

Key Concept

Commercial Vehicle Following Distance Rule (1 second per 10 feet + 1 second for 40+ mph)

Estimated Time:1m 0s

Question

Answer

Step-by-Step Solution

Key Concept

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