A driver is operating a 45\text{-foot} refrigerated straight truck at a steady cruising sp… — Commercial Driver's License (CDL) General Knowledge Exam

A driver is operating a $45\text{-foot}$ refrigerated straight truck at a steady cruising speed of $48\text{ mph}$ on a dry, two-lane rural highway under ideal weather conditions. Based on the standard commercial motor vehicle following distance rule, what is the minimum following distance, in seconds, the driver must maintain behind the lead vehicle?

Answer: 5.5 seconds

Answer

The minimum safe following distance is

5.5\text{ seconds}

Under standard commercial driving rules, a driver must maintain at least

1\text{ second}

for every

10\text{ feet}

of vehicle length when driving under

40\text{ mph}

, and add

1\text{ extra second}

for speeds at or above

40\text{ mph}

. For a

45\text{-foot}

truck traveling at

48\text{ mph}

, the base length requirement is

4.5\text{ seconds}

plus

1.0\text{ second}

for the speed factor, giving a total of

5.5\text{ seconds}

Step-by-Step Solution

Calculate the vehicle length time allowance using the base rule of

1\text{ second}

per

10\text{ feet}

of vehicle length.

\frac{45}{10} = 4.5\text{ seconds}

Commercial driver safety standards require

1\text{ second}

of space cushion for every

10\text{ feet}

of overall vehicle length.

Evaluate the vehicle speed to determine if an extra speed buffer is required.

48\text{ mph} \geq 40\text{ mph} \implies +1.0\text{ second}

At operating speeds at or above

40\text{ mph}

, drivers must add

1\text{ additional second}

to compensate for increased stopping distance.

Sum the vehicle length allowance and the high-speed adjustment to find total required following distance.

4.5\text{ seconds} + 1.0\text{ second} = 5.5\text{ seconds}

Combining the base interval and speed modifier yields the total minimum following buffer in seconds.

Key Concept

CDL Space Ahead Formula: 1 second per 10 feet of vehicle length plus 1 additional second when traveling at or above 40 mph.

Estimated Time:1m 0s

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