While transporting freight along a dry, multi-lane divided highway, a driver is operating … — Commercial Driver's License (CDL) General Knowledge Exam

While transporting freight along a dry, multi-lane divided highway, a driver is operating a $70$ -foot tractor-trailer combination at a steady speed of $50\text{ mph}$ . According to standard commercial vehicle safety guidelines, what is the minimum safe following distance, in seconds, that this driver must maintain behind the vehicle ahead?

A
$6\text{ seconds}$
B
$7\text{ seconds}$
$8\text{ seconds}$ Answer
D
$9\text{ seconds}$

Answer

8\text{ seconds}

Under standard commercial driver safety rules, the safe following interval is calculated by allowing

1\text{ second}

for every

10\text{ feet}

of vehicle length when traveling under

40\text{ mph}

, and adding

1\text{ additional second}

when traveling at or above

40\text{ mph}

. For a

70

-foot vehicle traveling at

50\text{ mph}

, the base requirement is

7\text{ seconds}

(

70 \div 10

), plus

1\text{ second}

for traveling above

40\text{ mph}

, resulting in a minimum safe following distance of

8\text{ seconds}

Step-by-Step Solution

Calculate the base following interval based on vehicle length.

70

-foot vehicle requires

\frac{70}{10} = 7\text{ seconds}

Commercial vehicle safety standards require

1\text{ second}

for every

10\text{ feet}

of vehicle length.

Evaluate operating speed and determine if a high-speed adjustment is necessary.

Since

50\text{ mph} \geq 40\text{ mph}

, add

1\text{ additional second}

Speeds of

40\text{ mph}

or greater require adding

1\text{ extra second}

to the total following distance.

Sum the base interval and the speed adjustment.

7\text{ seconds} + 1\text{ second} = 8\text{ seconds}

Adding these two components establishes the total minimum safe following interval under normal conditions.

Key Concept

CDL following distance formula based on vehicle length and highway travel speed.

Estimated Time:1m 0s

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