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Weight & Compliance • Client-Side Instant Math
Federal Bridge Formula & Axle Weight Legal Limit Calculator
Verify legal gross vehicle weight compliance using US DOT Federal Bridge Law B [W = 500(LN/(N-1) + 12N + 36)] and inspect individual axle scale tolerances.
#Bridge Formula B#Weigh Stations#Axle Limits#FMCSA Legal
Distance from center of steer axle to center of extreme rear trailer axle
CAT Scale / Platform Scale Weights (lbs)
Steer AxleMax 12,000 lbs
Drive TandemMax 34,000 lbs
Trailer TandemMax 34,000 lbs
Visual Axle Group Capacity Load
Steer Axle: 11,800 lbsPASS
Drive Tandem: 34,000 lbsPASS
Trailer Tandem: 33,400 lbsPASS
Live Calculation Output● Live Real-Time
FMCSA Weigh Station Status
100% LEGAL PASS
All axles and gross weight within federal legal bridge tolerances.
Actual Scale Gross79,400 lbsCurrent Scaled Total
Maximum Legal Cap80,000 lbsBridge Law & Statutory Limit
Individual Axle Group Tolerance
Steer Axle (Single):Compliant (≤ 12,000 lbs)
Drive Tandem Axles:Compliant (≤ 34,000 lbs)
Trailer Tandem Axles:Compliant (≤ 34,000 lbs)
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Mathematical Formula Breakdown
W = 500 × [ (L × N) / (N - 1) + 12N + 36 ], where W = Maximum legal weight on axle group, L = distance in feet between outer axles, and N = number of axles in group.
All calculations execute strictly according to standard federal transportation benchmarks and transparent mathematical constants with zero hidden padding.
Standard 5-Axle Semi-Truck Scale House Verification
A loaded tractor-trailer pulls onto a CAT scale with 51 feet outer wheelbase spacing (kingpin to steer axle span). The scale ticket shows Steer: 11,800 lbs, Drive Tandem: 34,400 lbs, Trailer Tandem: 33,200 lbs.
Gross weight = 11,800 + 34,400 + 33,200 = 79,400 lbs (Under 80k cap). However, Drive Tandem at 34,400 lbs exceeds the 34,000 lb tandem limit by 400 lbs! Sliding the trailer tandem forward or 5th wheel pin shifts weight legally to the trailer or steer axle before hitting the DOT weigh station.
Frequently Asked Questions
Expert Regulations & Calculations Q&A
Enacted under 23 CFR § 658.17, Bridge Formula B prevents highway bridge stress by ensuring heavy trucks distribute vehicle weight over sufficient length and axle counts.
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