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Federal Bridge Formula Axle Group Calculator

Calculate the federal bridge-formula result for an axle group from axle count and spacing; state caps, permits, and routing rules require separate review.

Inputs

Axle group and outer spacing

Range: at least 2 N

Enter a whole-number count of consecutive axles in the group. The formula uses N >= 2; fractional axle counts are invalid and flagged.

Range: at least 0.01 ft

Measure from the center of the first axle to the center of the last axle in the group, in feet.

Result

Rounded bridge-formula group result
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Unrounded formula result before 500-lb rounding
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Axle-count and limit note
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Federal bridge formula

Unrounded formula result before 500-lb rounding
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Rounded bridge-formula group result
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Estimates depend on the inputs and assumptions shown on each tool. Verify important figures against your records, contracts, and current official requirements.