Understand the federal Interstate limits for gross, single-axle and tandem weight, how the Bridge Formula can impose a lower maximum, and how drivers use scale tickets and load adjustments before dispatch.
Start with four separate legal checks
A truck can weigh less than 80,000 pounds and still be overweight. For ordinary operation on the Interstate System, planners and drivers must check gross vehicle weight, each single axle, each tandem axle and every relevant group of two or more consecutive axles under the Federal Bridge Formula. Tire, rim, suspension, manufacturer, state, route and posted-bridge limits add more checks. The lowest applicable limit controls.
The familiar federal limits apply to the Interstate starting point
Federal law generally limits gross vehicle weight to 80,000 pounds, a single axle to 20,000 pounds and a tandem axle to 34,000 pounds on the Interstate System. These numbers are ceilings, not automatic permission to load every combination to those amounts. Grandfather rights and special statutory provisions exist, while state and local rules can govern other highways.
Single and tandem axle have precise definitions
FHWA describes a single axle as one axle or axles whose centers are no more than 40 inches apart. A tandem is two or more consecutive axles whose centers are more than 40 inches but no more than 96 inches apart. Measure the actual configuration; a casual label such as spread axle does not replace the definition or a legal weight calculation.
The Bridge Formula protects structures from concentrated weight
The Federal Bridge Formula links the maximum weight on an axle group to the number of axles and the distance between the outer axles. Two trucks can have the same gross and axle weights but impose different stresses when one concentrates the load in a shorter wheelbase. More spacing or more axles can increase the formula allowance, subject to the other limits.
Know what the formula variables mean
FHWA expresses the formula as W = 500[(LN divided by N minus 1) + 12N + 36]. W is the maximum weight in pounds on the group, rounded through the federal method; L is the distance in feet between the outer axles in the group; and N is the number of axles. Use an official bridge table, approved software or trained compliance process instead of estimating from memory.
Every important consecutive axle group must pass
The formula does not test only the truck's first and last axles. FHWA explains that interior groups also must comply. On a typical five-axle tractor-semitrailer, the group covering the steering and drive axles, the full combination and the group from the drive axles through the trailer axles can all matter. A legal gross and two legal tandems do not prove the interior bridge group is legal.
FHWA's example shows why 80,000 can still fail
In FHWA's five-axle example, the truck totals 80,000 pounds, the steering axle carries 12,000 and each tandem carries 34,000. Yet the four-axle group from the drive through trailer axles weighs 68,000 pounds while its 35-foot spacing permits only 65,500 under the formula. Weight must be removed or the spacing increased; the legal total does not cure the violation.
The 36-foot tandem exception is narrow
Federal law allows two consecutive tandem sets to carry 34,000 pounds each when the distance from the first axle of the first tandem to the last axle of the second is at least 36 feet. This exception helps a common five-axle combination, but it does not override the 80,000-pound gross ceiling, axle ratings, tire limits, route restrictions or another applicable requirement.
There is no universal federal 12,000-pound steer limit
Many loading plans use 12,000 pounds as a practical steering-axle target, but the general federal single-axle ceiling is 20,000 pounds. The actual lawful steer weight may be lower because of tire load ratings, axle or suspension ratings, vehicle certification, state law or route restrictions. Read the equipment ratings and the jurisdictions involved instead of treating 12,000 as a universal law.
A scale ticket is a measurement, not a legal guarantee
A certified or commercial scale ticket can show steering, drive, trailer and gross weights at a particular time and configuration. It does not prove every bridge group, tire, route or state requirement is satisfied, and it cannot account for a later load shift, added fuel, ice, passengers or equipment. Keep the ticket as operational evidence, then complete the legal checks.
Weigh the truck in its dispatch-ready condition
Use the same tractor, trailer, driver equipment, pallets, dunnage, chains, tarps and other gear intended for the trip. Include realistic fuel and diesel exhaust fluid. A tractor scaled nearly empty can cross a limit after fueling; a reefer unit and its fuel also add weight. Record the unit numbers, time, fuel level and load status when the fleet procedure calls for it.
Read a three-platform ticket systematically
Compare the steer axle with its applicable limits, the drive tandem with the 34,000-pound federal ceiling and equipment limits, the trailer tandem with the same checks, and the gross with 80,000 pounds where those federal limits apply. Then test the relevant Bridge Formula groups and state or route limits. Do not stop when the bottom-line gross number is legal.
Moving the fifth wheel changes more than one axle
Sliding the fifth wheel generally transfers weight between the steering and drive axles. Movement direction, tractor geometry and equipment design determine the result. Follow manufacturer and carrier instructions, secure the mechanism completely and reweigh. Never trade a drive-axle violation for an overloaded steering axle, tire or front-axle rating.
Moving trailer tandems changes drive and trailer loading
Sliding the trailer tandems changes the lever relationship between the drive and trailer axle groups and also changes axle spacing. That can affect both scale weights and the Bridge Formula. Confirm pin engagement, air-line clearance, legal rear overhang and state kingpin-to-rear-axle or bridge requirements. Reweigh after adjustment rather than relying on a rule-of-thumb pounds-per-hole estimate.
Freight repositioning requires shipper and securement control
When axle adjustments cannot produce a legal result, the freight may need to be reworked or removed. Do not break a seal, move freight or operate loading equipment without authorization and training. Rebuild the securement system for the final distribution, close and seal the trailer correctly, document the change and inspect again before movement.
Cargo securement and weight compliance are separate duties
A well-secured load can still be overweight, and a legal axle distribution can still be inadequately secured. Concentrated freight, high centers of gravity, liquid surge and partial deliveries affect handling in addition to legal weight. Complete the federal and commodity-specific securement checks after the final loading arrangement; do not use securement as a substitute for weight correction.
Fuel burn is not a safe overweight plan
Fuel consumption usually reduces weight during a trip, but the amount and axle effect vary. A truck must be legal when it starts and whenever the requirement applies; a driver should not enter public roads overweight on the expectation that the engine will burn enough fuel before enforcement. Plan the loading and fueling together before dispatch.
Route law can be more restrictive than the Interstate ceiling
Federal limits discussed here govern the Interstate System and related federal access rules. Off the Interstate, states set many weight standards and may apply lower limits, seasonal frost restrictions, bridge postings, local truck routes, length rules or special tolerances. A legal Interstate combination may not be legal on the last mile. Verify every jurisdiction and posted sign.
Temporary postings and permits change the route decision
Construction, damage, weather or engineering review can produce a temporary lower bridge or road limit. A permit does not authorize a driver to ignore its route, dates, axle configuration, escort, speed or time conditions. The federal government does not issue routine state oversize or overweight permits; states administer their permit processes, often with separate local requirements.
An overweight permit is not a general freight solution
Permit eligibility varies, but overweight authority often centers on nondivisible loads and a specific configuration and route. Ordinary divisible freight may need to be reduced or split instead. Never assume a permit bought for one tractor, trailer, load or day transfers to another. Dispatch should verify the issuing authority's current terms before the truck moves.
A sealed load does not transfer the driver's duty
A shipper seal may limit access to cargo, but it does not turn an overweight vehicle into a legal one. If the scale result is not lawful, notify dispatch and the shipper, preserve the ticket and communications, and arrange an authorized rework or reduction. Do not accept pressure to continue because the bills show a lower estimated weight.
Handle scale discrepancies with controlled evidence
Different scales, uneven approaches, brakes, vehicle position and rounding can produce small differences. Use a properly maintained scale, place axle groups correctly, follow the operator's instructions and obtain a reweigh when needed. A close result deserves more margin, not less. If enforcement reports a different weight, follow the officer's instructions and the carrier's citation-review process.
Build a repeatable pre-dispatch weight workflow
Confirm expected cargo and equipment weight, choose the legal route, load for stable distribution, secure the freight, scale the dispatch-ready combination, check all axle and bridge groups, make authorized adjustments, reweigh and save the final ticket. Assign who approves exceptions and who verifies permits so the driver is not left to solve a planning failure at roadside.
Use current official sources for the actual trip
This guide reflects FHWA's Federal Bridge Formula guidance, 23 U.S.C. 127 and the federal size-and-weight framework available October 28, 2026. Grandfather provisions, specialized vehicles and state rules can change the answer. Verify current law, postings, permits, equipment ratings and carrier instructions for the exact combination and route. This article is educational, not legal or engineering advice.
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Official sources
FHWA: Federal Bridge Formula WeightsFHWA: Oversize/Overweight Load PermitsFHWA: Federal Size and Weight Program OverviewFHWA: Commercial Vehicle Size and Weight Questions and Answers23 U.S.C. 127: Vehicle Weight LimitationsCDL Truck Pro provides educational information. Confirm licensing, safety, tax, and regulatory requirements through current official sources and qualified professionals.