Glossary

Federal Bridge Formula

Last reviewed: 2026-05-20

Source review note: This term covers a compliance, regulatory, or enforcement topic where current rules, annual updates, or carrier policy may affect the correct answer. Use this as background only. Verify applicable regulations and carrier policy before making decisions.

A federal formula under 23 U.S.C. 127 that limits the weight carried by groups of axles on Interstates and other federal-aid highways, based on axle spacing. The formula prevents concentrated loads from damaging bridge structures. Single axle limit: 20,000 lb. Tandem axle limit: 34,000 lb. Gross vehicle weight limit: 80,000 lb (standard). Exceeding these limits is a violation even if individual tire and axle ratings are not exceeded.

Tire capacity and GAWR are equipment limits. Federal bridge formula limits are legal limits. Both apply independently — a load may exceed legal limits before tire limits are reached.

Real-World Use

A fleet dispatcher loading a dense shipment checks the axle weights against both the federal bridge limits and the vehicle's GAWR before confirming the load will be legal and within equipment ratings for the route.

Reference Sources

Sources used for context and verification of regulatory thresholds, inspection criteria, and compliance references on this page.

Gov 49 CFR 393.75 - Tires (Electronic Code of Federal Regulations, reviewed 2026-05-20)

What to Pair It With

Read this term with the full tire sidewall, vehicle rating information, manufacturer documentation, and the actual condition of the tire.

This site is for general information only. It does not replace professional tire service, DOT compliance advice, tire manufacturer instructions, vehicle manufacturer recommendations, or fleet policy.