Federal Bridge Formula and Axle Weights

Per-axle, tandem, and bridge-formula limits from axle weights and spacings.

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Formula and source

Federal Bridge Formula B: W = 500 × (LN / (N − 1) + 12N + 36) where W is the maximum allowed gross weight (lb) on a group of N consecutive axles spaced L feet apart. Single-axle limit 20 000 lb; tandem-axle limit 34 000 lb. Maximum gross 80 000 lb on Interstate routes.

23 CFR 658.17 by section (Federal-aid Highway Act of 1956 / FHWA Bridge Formula).

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