Truck Weight Regulations: A Complete Compliance Guide
Understanding weight regulations is essential for every carrier and driver. Being grossed out at 80,000 lbs is just one piece of the puzzle. This guide covers FMCSA weight regulations, the bridge formula, axle limits, permits, and penalties — everything you need to stay compliant.
Ahmad Qazi
Founder & CEO, O Trucking LLC
Fact-Checked by O Trucking Editorial Team
Written by Ahmad Qazi, founder of O Trucking LLC, drawing on 9+ years dispatching for owner-operators. Learn more about us.
O TruckingTruck Weight Regulations: A Complete Compliance Guide (2026)
Key Takeaways
- The federal gross vehicle weight limit on Interstate highways is 80,000 lbs for a standard 5-axle combination.
- Single axles are limited to 20,000 lbs and tandem axles (40-96 inch spacing) to 34,000 lbs.
- Bridge Formula B can restrict your load even when total GVW and individual axle weights are legal.
- Steer axles have no federal limit but are constrained by tire ratings, typically 12,000-14,000 lbs.
- Non-Interstate roads and posted bridges often carry far lower limits, sometimes 40,000 lbs or less.
- Overweight violations bring fines, possible out-of-service orders, and CSA score points.
Federal Weight Limits Overview
The Federal Highway Administration (FHWA) sets the baseline weight limits for Interstate highways. These limits are enforced by state DOT officers and highway patrol at weigh stations, roadside inspections, and portable scale checkpoints. The three key limits every driver must know:
80,000 lbs — Maximum gross vehicle weight for a 5-axle combination on Interstate highways.
20,000 lbs — Maximum single axle weight.
34,000 lbs — Maximum tandem axle weight (two axles, 40-96 inch spacing).
| Weight Type | Federal Limit | Notes |
|---|---|---|
| Gross vehicle weight (GVW) | 80,000 lbs | Standard 5-axle combination on Interstate highways |
| Single axle | 20,000 lbs | One axle carrying the full load |
| Tandem axle | 34,000 lbs | Two axles spaced 40-96 inches apart |
| Steer axle | 12,000-14,000 lbs* | No federal limit; set by tire ratings and many state laws |
*Steer axle figures reflect common tire ratings and state limits, not a single federal standard. Verify current limits with the FHWA and your state DOT.
Bridge Formula B Explained
The bridge formula is the most misunderstood weight regulation in trucking. Even experienced drivers get tripped up by it. The formula calculates the maximum allowable weight on any group of two or more consecutive axles based on the number of axles and the distance between the first and last axle in the group.
The purpose is to prevent excessive weight concentration that could damage bridge decks and supports. A truck that passes individual axle checks and total GVW checks can still violate the bridge formula if its axle spacing creates too much concentrated weight over a short distance.
In practice, this means the distance between your drive tandems and trailer tandems matters. Moving your trailer tandems farther back increases the distance in the formula, which raises the allowable weight. This is why experienced drivers know exactly where to position their tandems for different loads.
Steer Axle: The Often-Overlooked Limit
Overweight Permits and Exceptions
When your load exceeds standard limits, overweight permits allow legal transport on designated routes. Each state has its own permitting system, fees, and route restrictions. Common permit types include single-trip, annual, and blanket permits. Heavy haul carriers often maintain annual permits in multiple states for efficiency.
Exceptions to standard weight limits include emergency vehicles, certain agricultural vehicles during harvest season, and vehicles operating under federal emergency declarations. These exceptions are narrow and specific — do not assume your load qualifies without verifying. The state-by-state weight limits guide covers which states offer higher limits and under what conditions.
Know the Difference: Road Classification Matters
Common Weight-Compliance Mistakes to Avoid
- Checking only gross weight and ignoring the per-axle and Bridge Formula limits.
- Forgetting to slide the trailer tandems to rebalance after the trailer is loaded.
- Assuming the 80,000 lb Interstate limit applies on state, county, or posted-bridge roads.
- Not knowing your truck's empty tare weight, so you can't calculate true payload.
- Overloading the steer axle and risking front-tire blowouts and a citation.
Penalties and Enforcement
Overweight penalties vary dramatically by state but generally include per-pound fines, out-of-service orders, and points against the carrier's CSA score. Fines range from a few hundred dollars for minor overages to $10,000 or more for significant violations. Some states double fines for repeat offenders. In extreme cases, overweight violations can result in criminal charges.
The driver is typically cited at the point of enforcement, but the carrier bears the ultimate responsibility for loading compliance. Rate confirmations should clearly state weight limits, and drivers should weigh their loads before departing the shipper. For a detailed breakdown of state-level penalties, see the overweight fines guide.
Weight Regulations FAQ
Common questions about truck weight regulations and compliance
What are the federal axle weight limits for trucks?
Federal limits are 20,000 lbs on a single axle and 34,000 lbs on a tandem axle (two consecutive axles with centers spaced 40 to 96 inches apart). Steer axles are typically limited to 12,000-14,000 lbs based on tire ratings. The total gross vehicle weight cannot exceed 80,000 lbs on Interstate highways.
What is Bridge Formula B?
Bridge Formula B (W = 500 × ((LN / (N-1)) + 12N + 36)) calculates the maximum weight allowed on a group of axles based on the number of axles and the distance between the first and last axle. It prevents excessive weight concentration on bridges. You must comply with the bridge formula even if your total weight and individual axle weights are within limits.
What happens if a truck is overweight at a weigh station?
If a truck is found overweight, the driver may receive a citation, be placed out of service until weight is reduced, and face fines that vary by state. In some states, the driver must offload cargo at the weigh station before continuing. Overweight violations also affect the carrier's CSA score and can increase insurance rates.
Do weight regulations differ by road classification?
Yes. The federal 80,000 lb limit applies to Interstate highways. State highways, county roads, and local roads may have lower weight limits, especially on bridges and roads with seasonal restrictions. Some rural roads have limits as low as 40,000 lbs. Always check posted weight limits and state DOT resources for specific routes.
How much weight can a semi truck legally haul?
A standard 5-axle tractor-trailer is capped at 80,000 lbs gross vehicle weight on Interstate highways. Because an empty tractor-trailer typically weighs about 30,000-35,000 lbs (tractor plus empty trailer), the legal payload is usually around 45,000 lbs once you account for fuel, driver, and equipment. The exact figure depends on your truck's tare weight, so weigh empty to know your true available payload.
How can I avoid overweight violations at a weigh station?
Weigh your loaded truck on a certified scale before leaving the shipper, confirm both your gross and individual axle weights are within limits, and slide your tandems to balance the load and satisfy Bridge Formula B. Keep your truck's empty tare weight on file so you know your payload ceiling, and verify weight limits for every road segment on your route — not just the Interstate portion.
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