Federal Bridge Formula Calculator
Compute maximum legal gross vehicle weights under Title 23, CFR Part 658 by axle geometry and outer axle spacing. Prevents premature bridge structural stress and heavy DOT scale citations.
23 CFR § 658
Axle configuration
W = 500 [LN/(N-1) + 12N + 36]Number of axles in measured group
5
2 axles (tandem)5 axles (standard semi)9 axles (heavy haul)
Center-to-center distance in feet
51 ft
4 ft (close tandem)36 ft (trailer group)70 ft (full combination)
Standard commercial rig presets
Federal weight limits matrix
| Axle configuration | Legal max |
|---|---|
| Single axle | 20,000 lbs |
| Tandem axle (40 to 96 in) | 34,000 lbs |
| Interstate gross cap (GVW) | 80,000 lbs |
Frequently Asked Questions About Federal Bridge Weight Limits
- What is the Federal Bridge Gross Weight Formula (23 CFR § 658)?
- The federal formula is W = 500 * [ (L * N) / (N - 1) + 12N + 36 ], where W is maximum weight in pounds, L is distance in feet between outer axles, and N is the number of consecutive axles. It prevents excessive pavement and bridge girder deflection.
- What is the maximum legal gross vehicle weight without an overweight permit?
- On the U.S. Interstate Highway System, the non-permitted maximum gross vehicle weight (GVW) is capped at 80,000 lbs. Standard federal limits also specify 20,000 lbs on single axles and 34,000 lbs on tandem axle groups spaced 40 to 96 inches apart.
- What penalties apply for violating federal axle spacing weight limits?
- Exceeding bridge formula limits can result in roadside state police or DOT scale citations with escalating fines per pound of overweight, potential civil fines, and immediate Out-of-Service (OOS) orders requiring load re-distribution or superload permit acquisition.