A commercial driver is piloting a 65-foot tractor-trailer combination at 48\text{ mph} alo… — Commercial Driver's License (CDL) General Knowledge Exam

A commercial driver is piloting a $65$ -foot tractor-trailer combination at $48\text{ mph}$ along a dry, multi-lane highway. A passenger vehicle abruptly changes lanes into the space cushion ahead, reducing the following gap to $4.5\text{ seconds}$ . According to standard commercial vehicle safety rules, how many additional seconds of following distance must the driver create to re-establish the minimum recommended space ahead?

A
$2.0$ additional seconds
B
$1.0$ additional second
$3.0$ additional secondsAnswer
D
$4.0$ additional seconds

Answer

The driver must create

3.0

additional seconds of following distance to restore the total required

7.5

-second space cushion.

Under standard commercial driving regulations, safe following distance is calculated as

1\text{ second}

for every

10\text{ feet}

of vehicle length, with

1\text{ extra second}

added when driving at speeds of

40\text{ mph}

or greater. For a

65

-foot vehicle traveling at

48\text{ mph}

, the minimum required space ahead is

6.5 + 1.0 = 7.5\text{ seconds}

. Because the cut-in vehicle left only a

4.5

-second gap, the driver must ease off the accelerator to open an additional

3.0\text{ seconds}

(

7.5 - 4.5 = 3.0

Step-by-Step Solution

Calculate the base following distance required for vehicle length.

\frac{65\text{ ft}}{10\text{ ft/sec}} = 6.5\text{ seconds}

Commercial driver guidelines dictate allowing at least

1\text{ second}

for each

10\text{ feet}

of vehicle length under

40\text{ mph}

Apply the speed modifier for travel at or above

40\text{ mph}

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

For speeds at or above

40\text{ mph}

, exactly

1\text{ additional second}

must be added to the base length calculation.

Determine the required gap adjustment by subtracting the current space cushion.

7.5\text{ seconds} - 4.5\text{ seconds} = 3.0\text{ seconds}

The difference between the total mandated space cushion and the current interval represents the additional time gap the driver must regain.

Key Concept

Calculating required commercial vehicle following distance using the length-to-time formula (

1\text{ second}

per

10\text{ feet}

plus

1\text{ second}

for

\ge 40\text{ mph}

) and adjusting space cushions dynamically.

Estimated Time:1m 30s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

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