What is Federal Bridge Formula B in heavy haul trucking?

Federal Bridge Formula B is a mathematical formula [W = 500 * (LN / (N - 1) + 12N + 36)] enacted by Congress to prevent commercial vehicles from overstressing highway bridges. It determines the maximum allowable gross weight on any group of two or more consecutive axles based on the distance (L in feet) between the outer axles and the number of axles (N) in the group.

How does a booster or flip axle equalize weight across trailer axles?

A hydraulic or nitrogen-equalized booster axle extends the trailer wheelbase and transfers weight away from the primary trailer axle group to the auxiliary axle. By increasing outer axle spacing (L), carriers can legally permit higher gross payloads under state bridge and axle-loading statutes.

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Multi-Axle Heavy Haul & Lowboy Axle Weight Distribution Calculator

Engineer heavy haul axle configurations with precision: calculate steer, drive, trailer, and booster axle weights, evaluate payload center of gravity offsets, and verify compliance with Federal Bridge Formula B.

Center of Gravity (CG) Centering

Placing an 85,000 lb excavator just 18 inches too far forward can overload the tractor drive group by 9,000 lbs while underloading the trailer group, resulting in failed state weigh station inspections.

Booster & Spreader Bar Physics

Hydraulic flip axles and pin-on boosters redistribute weight across extended wheelbases. Exspeedite models axle group geometry to ensure equalized load sharing across every tire line.

Federal Bridge Formula B

Avoid catastrophic overweight citations. Instantly calculate whether your combination length and axle count satisfy federal and state bridge formula statutes before rolling out of the yard.

Interactive Multi-Axle Load Distribution & Bridge Formula Modeler

Trailer & Axle Configuration:

Empty Tractor & Trailer Tare Weight (lbs):

Payload / Machinery Weight (lbs):

Trailer Deck / Well Length (ft):

Center of Gravity Offset from Deck Center (inches): Negative = Forward towards tractor | Positive = Rear towards trailer

Outer Axle Group Wheelbase (Steer to Rearmost Axle in ft):

Calculated Axle Group Loadings & Bridge Compliance

Steer Axle:

12,800 lbs

LEGAL

Tractor Drive Group:

42,500 lbs

PERMITTED TANDEM

Trailer Axle Group:

52,700 lbs

PERMITTED TRIDEM

Booster / Aux Axle:

12,000 lbs

ACTIVE

Gross Combination Weight (GCW):

120,000 lbs

Federal Bridge Formula B Max Capacity:

128,500 lbs

Bridge Formula Status:

COMPLIANT (PASS)

Multi-Axle Weight Limits & Permit Thresholds

Axle Configuration	Federal Standard Limit	State Routine Permit Limit	Superload Review Threshold	Standard Tire Rating (lbs/in)
Steer Single Axle	12,000 – 20,000 lbs	Up to 20,000 lbs	> 20,000 lbs	600 – 650 lbs / inch
Drive Tandem (2 Axles)	34,000 lbs	40,000 – 46,000 lbs	> 48,000 lbs	500 – 600 lbs / inch
Tridem Group (3 Axles)	42,000 lbs	50,000 – 60,000 lbs	> 60,000 lbs	500 – 600 lbs / inch
Quad Axle Group (4 Axles)	50,000 lbs	65,000 – 72,000 lbs	> 72,000 lbs	500 – 600 lbs / inch
Booster / Flip Axle (1 Axle)	20,000 lbs	20,000 – 25,000 lbs	Equalized Hydraulic Sync	500 – 600 lbs / inch

Eliminate Axle Overload Citations in Your Heavy Haul Operations

Pre-dispatch axle validation prevents scale tickets, blown tires, and costly road-side reloads. Learn how Exspeedite TMS calculates multi-axle configurations automatically upon load tender.

Full Name *

Carrier / Heavy Transport Company *

Corporate Work Email *

Direct Phone *

Primary Machinery / Cargo Hauled

Maximum Axle Combinations Operated