When operating a 75\text{-foot} commercial combination vehicle at a steady speed of 45\tex… — Commercial Driver's License (CDL) General Knowledge Exam

When operating a $75\text{-foot}$ commercial combination vehicle at a steady speed of $45\text{ mph}$ on a dry highway, a driver who counts $8\text{ seconds}$ from the moment the vehicle ahead passes a fixed landmark to the moment their front bumper reaches that landmark has established an adequate following distance according to standard CDL guidelines.

Answer: Answer

Answer

False. The minimum required safe following distance is

8.5\text{ seconds}

, making an

8\text{-second}

interval insufficient.

According to the CDL safety manual, commercial vehicles require at least

1\text{ second}

per

10\text{ feet}

of vehicle length plus an extra

1\text{ second}

for speeds of

40\text{ mph}

or greater. A

75\text{-foot}

vehicle at

45\text{ mph}

requires a minimum following distance of

8.5\text{ seconds}

(

7.5\text{ s} + 1.0\text{ s}

). Therefore, an

8\text{-second}

count leaves an inadequate space cushion, making the statement false.

Step-by-Step Solution

Calculate the baseline following time based on total vehicle length

\frac{75\text{ ft}}{10\text{ ft/s}} = 7.5\text{ seconds}

Standard commercial driving safety guidelines mandate a baseline cushion of

1\text{ second}

for every

10\text{ feet}

of vehicle length.

Determine and apply the speed modifier

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

Because the vehicle is traveling at

45\text{ mph}

(which is at or above

40\text{ mph}

), an additional

1\text{ second}

must be added to the baseline time gap.

Compare the driver's measured following gap with the required minimum gap

8.0\text{ seconds} < 8.5\text{ seconds}

The driver's counted interval of

8\text{ seconds}

is less than the calculated minimum safe requirement of

8.5\text{ seconds}

, meaning the cushion is inadequate.

Key Concept

CDL Following Distance Calculation (

1\text{ second}

per

10\text{ feet}

of length plus

1\text{ second}

for speeds at or above

40\text{ mph}

)

Estimated Time:1m 0s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

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