What it means
On the Interstate System, 23 CFR 658.17 sets 80,000 lb gross, 20,000 lb on a single axle and 34,000 lb on a tandem, and limits any group of consecutive axles to W = 500 (LN/(N-1) + 12N + 36), where W is the weight in pounds, L the distance in feet between the outer axles of the group and N the number of axles.[1]
The FHWA stresses the key point: two or more consecutive axles may not exceed the formula weight even when single axles, tandems and gross weight are within limits, and interior groups such as the tractor's or the trailer's axles must comply too.[2] A tandem, for these rules, is two or more consecutive axles more than 40 and not more than 96 inches apart.[3]
Example
A tractor-trailer weighs 78,000 lb in total, under the 80,000 lb gross limit, but dense cartons loaded at the rear put 35,500 lb on the trailer tandem. It fails on the tandem despite a legal gross, and the fix is to move freight forward and re-weigh.
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Related freight problems
Related guides
Sources
- Legal Information Institute, Cornell Law School, “23 CFR § 658.17, Weight,” Federal regulation. Accessed September 2026.
- Federal Highway Administration, “Bridge Formula Weights,” Government guidance. Accessed September 2026.
- Legal Information Institute, Cornell Law School, “23 CFR § 658.5, Definitions (axle weights),” Federal regulation. Accessed September 30, 2026.
General operational information, not legal, customs or regulatory advice. Rules and rates change; confirm current requirements with the agency, carrier or contract that governs your shipment.