Federal Bridge Law
Regulations governing maximum weight allowed on a truck's axle groups based on spacing.
Definition
The Federal Bridge Law (also called Bridge Formula) sets the maximum weight that a commercial vehicle can carry on any group of axles based on the distance between those axles. This protects bridges and road surfaces from damage. The formula is: W = 500(LN/(N-1) + 12N + 36), where W is weight, L is distance between axle groups, and N is number of axles. Practical result: tandem slide position directly affects legal weight per axle.
Why it matters to you
Federal bridge law limits weight by axle spacing, not just total weight, which is why a legal-gross truck can still be illegal at the scale. It exists to protect bridge structures. Practically, it means understanding how your tandem position and load placement interact before you get weighed — and knowing that state rules add their own limits on top.
FAQ
What does Federal Bridge Law mean?
Regulations governing maximum weight allowed on a truck's axle groups based on spacing.
Why does Federal Bridge Law matter to a driver?
Federal bridge law limits weight by axle spacing, not just total weight, which is why a legal-gross truck can still be illegal at the scale. It exists to protect bridge structures. Practically, it means understanding how your tandem position and load placement interact before you get weighed — and knowing that state rules add their own limits on top.
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