A five-axle tractor-semitrailer combination is being prepared for an interstate trip. The … — Commercial Driver's License (CDL) General Knowledge Exam

A five-axle tractor-semitrailer combination is being prepared for an interstate trip. The vehicle and its axle groups have the following specifications:

- Gross Combination Weight Rating (GCWR): $85{}000\text{ lbs}$
- Steer axle Gross Axle Weight Rating (GAWR): $12{}500\text{ lbs}$
- Drive tandem axle GAWR: $38{}000\text{ lbs}$
- Trailer tandem axle GAWR: $36{}000\text{ lbs}$

The combination has a total empty (tare) weight of $31{}600\text{ lbs}$ , distributed as follows: steer axle = $10{}200\text{ lbs}$ , drive tandem = $11{}800\text{ lbs}$ , and trailer tandem = $9{}600\text{ lbs}$ .

When loaded, the freight will distribute additional weight such that $5\%$ is placed on the steer axle, $45\%$ on the drive tandem axle, and $50\%$ on the trailer tandem axle. Under standard federal interstate weight regulations ( $80{}000\text{ lbs}$ gross, $20{}000\text{ lbs}$ single axle, $34{}000\text{ lbs}$ tandem axle), what is the maximum cargo weight in pounds that can be legally loaded without exceeding any federal statutory weight limit or manufacturer axle rating?

Answer: 46000 lbs

Answer

46,000 pounds

The maximum legal cargo weight is

46{}000\text{ lbs}

, governed by the steer axle GAWR of

12{}500\text{ lbs}

. With an empty steer weight of

10{}200\text{ lbs}

and a

5\%

cargo distribution factor, the steer axle can accept at most

2{}300\text{ lbs}

of added load (

\frac{2{}300}{0.05} = 46{}000\text{ lbs}

). Loading any amount above

46{}000\text{ lbs}

causes the steer axle to exceed its manufacturer rating, even though the drive tandems, trailer tandems, and total gross combination weight remain below their legal maximums.

Step-by-Step Solution

Determine the governing legal limit for each axle group and combination total by taking the minimum of manufacturer ratings and statutory limits.

Steer axle =

12{}500\text{ lbs}

; Drive tandem =

34{}000\text{ lbs}

; Trailer tandem =

34{}000\text{ lbs}

; Gross combination =

80{}000\text{ lbs}

Commercial motor vehicles must adhere to whichever is lower: manufacturer structural ratings (GAWR/GCWR) or federal statutory operating limits.

Calculate remaining load capacities for each axle group and the total gross weight.

Steer margin =

2{}300\text{ lbs}

; Drive tandem margin =

22{}200\text{ lbs}

; Trailer tandem margin =

24{}400\text{ lbs}

; Gross combination margin =

48{}400\text{ lbs}

Subtracting tare axle weights from effective limits determines how much additional weight each component can support.

Divide each component's margin by its respective load distribution percentage to determine the maximum total cargo supported.

Steer limit:

\frac{2{}300}{0.05} = 46{}000\text{ lbs}

; Drive tandem limit:

\frac{22{}200}{0.45} \approx 49{}333\text{ lbs}

; Trailer tandem limit:

\frac{24{}400}{0.50} = 48{}800\text{ lbs}

; Gross limit:

48{}400\text{ lbs}

Cargo weight is distributed proportionally across axles, meaning an individual axle may reach its legal limit before gross weight is reached.

Identify the minimum among all calculated cargo weight capacities.

Maximum legal cargo weight =

46{}000\text{ lbs}

The steer axle GAWR serves as the binding constraint (

46{}000\text{ lbs} < 48{}400\text{ lbs}

), preventing the vehicle from loading to the full gross federal limit.

Key Concept

Interaction between statutory federal weight limits, manufacturer ratings (GAWR/GCWR), and axle load distribution

Alternative Method

Work backwards by testing the gross weight limit (

48{}400\text{ lbs}

) across all axles to check for violations: Steer load would be

10{}200 + 0.05(48{}400) = 12{}620\text{ lbs}

(overload by

120\text{ lbs}

). Reduce the cargo by

\frac{120}{0.05} = 2{}400\text{ lbs}

, yielding

48{}400 - 2{}400 = 46{}000\text{ lbs}

Estimated Time:2m 0s

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