While traveling at 55\text{ mph} on a dry rural highway, the driver of a 50-foot commercia… — Commercial Driver's License (CDL) General Knowledge Exam

While traveling at $55\text{ mph}$ on a dry rural highway, the driver of a $50$ -foot commercial flatbed tracks a highway bridge shadow to verify following distance. To maintain safe space ahead under ideal driving conditions, how many seconds must elapse from the moment the vehicle ahead crosses the shadow until the flatbed reaches it?

A
At least $5\text{ seconds}$
B
At least $2\text{ seconds}$
At least $6\text{ seconds}$ Answer
D
At least $10\text{ seconds}$

Answer

At least

6\text{ seconds}

According to CDL standards, a driver must maintain at least

1\text{ second}

for each

10\text{ feet}

of vehicle length when traveling under

40\text{ mph}

, and add

1\text{ extra second}

for speeds at or above

40\text{ mph}

. For a

50

-foot vehicle at

55\text{ mph}

, the base distance is

5\text{ seconds}

(

50 \div 10

), plus

1\text{ second}

for driving over

40\text{ mph}

, yielding a minimum safe following distance of at least

6\text{ seconds}

Step-by-Step Solution

Calculate the base following distance interval from vehicle length.

50\text{ feet} \div 10\text{ feet/second} = 5\text{ seconds}

The commercial vehicle guideline requires allowing

1\text{ second}

for every

10\text{ feet}

of vehicle length at speeds under

40\text{ mph}

Apply the speed-based adjustment for highway operation.

5\text{ seconds} + 1\text{ second} = 6\text{ seconds}

When traveling at speeds of

40\text{ mph}

or greater,

1\text{ additional second}

must be added for safety.

Apply the landmark timing method.

The driver must count at least

6\text{ seconds}

after the rear of the lead vehicle passes the shadow before the flatbed reaches it.

Using a stationary landmark allows the driver to accurately measure the actual following time gap.

Key Concept

CDL Following Distance Formula and Landmark Timing

Estimated Time:1m 0s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

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