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

A five-axle tractor-semitrailer combination is being prepared for an interstate freight haul. The vehicle configuration and ratings are specified as follows:

- Steering axle: Gross Axle Weight Rating (GAWR) of $12{}000\text{ lbs}$ , fitted with $2$ steer tires rated at $5{}750\text{ lbs}$ each
- Drive tandem axle: GAWR of $38{}000\text{ lbs}$ , fitted with $8$ tires rated at $4{}500\text{ lbs}$ each
- Trailer tandem axle: GAWR of $36{}000\text{ lbs}$ , fitted with $8$ tires rated at $4{}500\text{ lbs}$ each
- Manufacturer Gross Combination Weight Rating (GCWR): $80{}000\text{ lbs}$
- Total empty (unladen/tare) weight of the combination: $31{}500\text{ lbs}$

Assuming the cargo can be distributed across the axles in any required proportion and standard federal interstate weight limits apply ( $20{}000\text{ lbs}$ single axle, $34{}000\text{ lbs}$ tandem axle, and $80{}000\text{ lbs}$ gross vehicle combination), what is the maximum legal cargo payload, in pounds ( $\text{lbs}$ ), that this combination can transport without violating any tire rating, manufacturer rating, or federal statutory limit?

Answer: 48000 lbs

Answer

48,000 lbs

To find the maximum allowable payload, every component constraint must be evaluated. The steer axle is limited by tire capacity to

11{}500\text{ lbs}

(

2 \times 5{}750\text{ lbs}

), while the drive and trailer tandems are limited by federal statutory caps to

34{}000\text{ lbs}

each. The maximum achievable legal combination weight is

11{}500 + 34{}000 + 34{}000 = 79{}500\text{ lbs}

, which is under the

80{}000\text{ lbs}

federal gross limit and GCWR. Subtracting the unladen weight of

31{}500\text{ lbs}

from

79{}500\text{ lbs}

yields exactly

48{}000\text{ lbs}

of allowable payload.

Step-by-Step Solution

Determine the governing weight limit for the steering axle.

11,500 lbs

The legal limit is the lowest of the statutory single axle limit (20,000 lbs), manufacturer GAWR (12,000 lbs), and cumulative tire load capacity (2 tires × 5,750 lbs = 11,500 lbs).

Determine the governing weight limits for the drive and trailer tandem axles.

34,000 lbs for drive tandem; 34,000 lbs for trailer tandem

Federal statutory limits cap tandem axles at 34,000 lbs, which is lower than both the manufacturer GAWRs (38,000 lbs and 36,000 lbs) and cumulative tire ratings (36,000 lbs).

Calculate the maximum allowable Gross Combination Weight (GCW).

79,500 lbs

Summing the maximum legal individual axle loads yields 11,500 lbs + 34,000 lbs + 34,000 lbs = 79,500 lbs. Because this is lower than the 80,000 lbs federal bridge cap and manufacturer GCWR, 79,500 lbs is the maximum legal gross weight.

Calculate the maximum allowable cargo payload.

48,000 lbs

Subtracting the unladen tare weight (31,500 lbs) from the maximum legal gross weight (79,500 lbs) gives 48,000 lbs.

Key Concept

Under CDL regulations, vehicle operating limits are governed by the most restrictive constraint among manufacturer GAWR/GCWR, total tire load ratings, and statutory federal bridge weight limits.

Estimated Time:1m 30s

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