While operating a 35\text{-foot} single-unit commercial motorcoach at a constant speed of … — Commercial Driver's License (CDL) General Knowledge Exam

While operating a $35\text{-foot}$ single-unit commercial motorcoach at a constant speed of $45\text{ mph}$ on a clear, dry highway, what is the minimum following distance in seconds that the driver must maintain behind the vehicle ahead?

A
$3.5\text{ seconds}$
B
$2.0\text{ seconds}$
$4.5\text{ seconds}$ Answer
D
$5.5\text{ seconds}$

Answer

The minimum safe following distance is

4.5\text{ seconds}

According to official CDL guidelines, commercial drivers must allow at least

1\text{ second}

for every

10\text{ feet}

of vehicle length when traveling under

40\text{ mph}

. For a

35\text{-foot}

vehicle, this yields

3.5\text{ seconds}

. Because the vehicle is traveling at

45\text{ mph}

(which is at or above

40\text{ mph}

1\text{ additional second}

must be added, totaling

4.5\text{ seconds}

Step-by-Step Solution

Calculate base following interval based on vehicle length

\frac{35\text{ feet}}{10\text{ feet/second}} = 3.5\text{ seconds}

The standard CDL formula requires 1 second of space ahead for every 10 feet of vehicle length.

Determine speed adjustment for operating at or above 40 mph

Add

1.0\text{ second}

because the operating speed is

45\text{ mph}

When operating at speeds of 40 mph or greater, drivers must add 1 additional second to account for increased stopping distance.

Sum base interval and speed adjustment

3.5\text{ seconds} + 1.0\text{ second} = 4.5\text{ seconds}

Total required following distance under ideal conditions is the sum of the length-based time and the speed modifier.

Key Concept

CDL Safe Following Distance Rule (1 second per 10 feet of vehicle length, plus 1 second for speeds at or over 40 mph)

Estimated Time:1m 0s

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