Bridge Formula & State Size/Weight Compliance Checks

The Federal Bridge Formula, W = 500 × (LN/(N−1) + 12N + 36), limits the weight on any group of two or more consecutive axles based on how many axles there are and how far apart the outer axles sit. The limits are 20,000 lb on a single axle, 34,000 lb on a tandem and 80,000 lb gross on the Interstate. States add their own rules on top, and those rules often differ off the Interstate.

What the check includes

• Bridge formula check for every consecutive axle group, not just the outer bridge
• Single, tandem, tridem and gross limits for the route type
• State-specific weight limits and exceptions for the states you name
• State size limits (length, width, height, kingpin setback) for the states you name
• Lift-axle and pusher-axle rules that apply to your configuration
• A clear list of which checks pass, which fail, and by how much
• Practical fixes: axle spacing, slide position, load position or axle count

When you need it

Designing a new trailer or axle configuration, adding a lift axle, running a combination in several states, or answering a customer or permit office that asks for a documented compliance check.

Important limits

This check covers legal size and weight limits for the configuration and states you list. Permits, seasonal restrictions and local posted bridges are handled by the carrier and the permitting agency. Where a state rule is unclear, the report says so.

You can run a quick federal check yourself with the Bridge Law Calculator quick check.