Two commercial drivers are traveling on a clear, dry highway at a steady speed of 55\text{… — Commercial Driver's License (CDL) General Knowledge Exam

Two commercial drivers are traveling on a clear, dry highway at a steady speed of $55\text{ mph}$ . Driver A is operating a $40$ -foot straight truck, while Driver B is operating an $80$ -foot combination vehicle. According to standard commercial vehicle space management formulas, Driver B is required to maintain exactly double the forward following distance (measured in seconds) compared to Driver A.

Answer: Answer

Answer

False

The correct answer is False. While an

80

-foot vehicle is twice as long as a

40

-foot vehicle, the required following distance at speeds over

40\text{ mph}

includes a flat

1\text{-second}

addition for safety. Driver A requires

5\text{ seconds}

(

4\text{ seconds}

for length +

1\text{ second}

for speed), while Driver B requires

9\text{ seconds}

(

8\text{ seconds}

for length +

1\text{ second}

for speed). Because the

1\text{-second}

speed penalty is a constant addition rather than a multiplier,

9\text{ seconds}

is not exactly double

5\text{ seconds}

Step-by-Step Solution

Calculate the base following distance for Driver A (

40

-foot vehicle).

\frac{40}{10} = 4\text{ seconds}

The base standard is

1\text{ second}

of following distance for every

10\text{ feet}

of vehicle length.

Apply the high-speed safety modifier for Driver A.

4\text{ seconds} + 1\text{ second} = 5\text{ seconds}

Because the vehicle is traveling at

55\text{ mph}

(which is

\ge 40\text{ mph}

), exactly

1\text{ additional second}

must be added.

Calculate the base following distance for Driver B (

80

-foot vehicle).

\frac{80}{10} = 8\text{ seconds}

Applying the same base standard of

1\text{ second}

per

10\text{ feet}

of vehicle length.

Apply the high-speed safety modifier for Driver B.

8\text{ seconds} + 1\text{ second} = 9\text{ seconds}

The vehicle is also traveling at

55\text{ mph}

, requiring the identical flat

1\text{-second}

addition.

Compare Driver B's total required time to Driver A's total required time.

9\text{ seconds} \neq 2 \times 5\text{ seconds}

The statement claims the required time is exactly double, which is mathematically false due to the non-proportional constant added to both.

Key Concept

Commercial Vehicle Following Distance Formula and High-Speed Modifier Proportionality

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

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