A commercial combination vehicle with an overall length of 75\text{ feet} is cruising at 5… — Commercial Driver's License (CDL) General Knowledge Exam

A commercial combination vehicle with an overall length of $75\text{ feet}$ is cruising at $50\text{ mph}$ along a highway. The driver tracks a stationary overhead sign to measure following distance behind a lead truck, noting that exactly $6.0\text{ seconds}$ elapse between when the lead truck passes under the sign and when the driver's front bumper reaches it. According to commercial driving space management standards, how does this measured interval compare to the minimum required following distance, and what action should the driver take?

A
The vehicle is following too closely; the driver is $1.5\text{ seconds}$ below the required $7.5\text{-second}$ buffer and must increase following distance.
B
The vehicle maintains an adequate buffer; $6.0\text{ seconds}$ exceeds the standard commercial minimum requirement of $4.0\text{ seconds}$ for reaction and braking.
The vehicle is following too closely; the driver is $2.5\text{ seconds}$ below the required $8.5\text{-second}$ buffer and must increase following distance.Answer
D
The vehicle is following too closely; the driver is $3.5\text{ seconds}$ below the required $9.5\text{-second}$ buffer and must increase following distance.

Answer

The vehicle is following too closely; the driver is

2.5\text{ seconds}

below the required

8.5\text{-second}

buffer and must increase following distance.

For a

75\text{-foot}

commercial vehicle, the base following distance is

7.5\text{ seconds}

(

1\text{ second}

per

10\text{ feet}

). Because operating speed is

50\text{ mph}

(which meets or exceeds the

40\text{ mph}

threshold),

1\text{ additional second}

is required, establishing a total minimum buffer of

8.5\text{ seconds}

. With an observed gap of

6.0\text{ seconds}

, the vehicle is operating with a

2.5\text{-second}

deficit and must increase space ahead.

Step-by-Step Solution

Calculate the base following distance based on overall vehicle length.

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

Commercial driving standards require at least

1\text{ second}

of following distance for every

10\text{ feet}

of vehicle length at speeds under

40\text{ mph}

Apply the speed-dependent modifier for operating at speeds of

40\text{ mph}

or higher.

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

Because the vehicle is traveling at

50\text{ mph}

(which is

\geq 40\text{ mph}

), exactly

1\text{ additional second}

must be added to the base calculation.

Compare the actual measured following interval against the calculated requirement and determine corrective action.

8.5\text{ seconds (required)} - 6.0\text{ seconds (measured)} = 2.5\text{ seconds (deficit)}

The measured interval of

6.0\text{ seconds}

2.5\text{ seconds}

short of the required

8.5\text{ seconds}

, meaning the driver must decelerate or adjust throttle to increase following distance.

Key Concept

Commercial vehicle following distance calculation:

1\text{ second}

per

10\text{ feet}

of vehicle length, plus

1\text{ extra second}

for speeds at or above

40\text{ mph}

Estimated Time:2m 0s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic