A driver is operating a 50\text{-foot} commercial delivery vehicle at a steady cruising sp… — Commercial Driver's License (CDL) General Knowledge Exam

A driver is operating a $50\text{-foot}$ commercial delivery vehicle at a steady cruising speed of $55\text{ mph}$ along a clear, dry multi-lane divided highway. Under standard commercial driver space management guidelines, what is the minimum safe following distance the driver must maintain behind the lead vehicle?

A
$4\text{ seconds}$
B
$5\text{ seconds}$
$6\text{ seconds}$ Answer
D
$8\text{ seconds}$

Answer

6\text{ seconds}

According to the official CDL guidelines, a driver should allow at least

1\text{ second}

for every

10\text{ feet}

of vehicle length at speeds under

40\text{ mph}

. For a

50\text{-foot}

vehicle, this base requirement is

5\text{ seconds}

. Because the vehicle is traveling at

55\text{ mph}

(which is at or above

40\text{ mph}

), an additional

1\text{ second}

must be added, resulting in a total minimum following distance of

6\text{ seconds}

Step-by-Step Solution

Calculate base following time based on vehicle length

50\text{ ft} \div 10\text{ ft/sec} = 5\text{ seconds}

The commercial vehicle guideline requires at least

1\text{ second}

for each

10\text{ feet}

of vehicle length.

Evaluate operating speed to determine if speed adjustments apply

Traveling at

55\text{ mph}

, which is

\ge 40\text{ mph}

, requires

+1\text{ second}

For speeds at or above

40\text{ mph}

, an extra

1\text{ second}

must be added to provide adequate braking and maneuvering space.

Sum the base time and the high-speed adjustment

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

The total following distance represents the minimum safe time cushion under ideal conditions.

Key Concept

CDL Following Distance Formula

Estimated Time:1m 0s

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