Montana Truck Weight Limits

How much a truck can weigh in Montana

On the Interstate you are held to 80,000 pounds. Off it, Montana lets divisible loads run up to 131,060 pounds on its Designated Highway Network, limited by the federal bridge formula and your axle count (MCA 61-10-107; 23 CFR 658 App. C). Overweight fines are flat brackets that top out at $2,000 for anything more than 25,000 pounds over (MCA 61-10-145).

Axles, off-Interstate, and permits

• Off the Interstate: Up to 131,060 lb on the Designated Highway Network for divisible loads that meet the federal bridge formula (with permit and GVW fees)
• Single axle: 20,000 lb
• Tandem axle: 34,000 lb
• With a permit: 131,060 lb (Rocky Mountain doubles and multi-axle combinations, capped by the federal bridge formula); non-divisible superloads higher case-by-case
• Montana's 131,060-lb figure is grandfathered onto its Interstates and state routes (23 CFR 658 App. C) as a western resource-hauling state. The number is a bridge-formula ceiling, not a flat cap, so an actual load's max depends on axle spacing.

Posted bridge and road limits

Local authorities and MDT post bridges and roads with MUTCD 'WEIGHT LIMIT X TONS' signs. Tons are 2,000-pound short tons, so 15 TONS is 30,000 pounds. The posted number overrides your legal weight, so a fully legal 80,000-pound rig still cannot cross a low-posted bridge. Crossing over the posted limit is a separate charge on top of the weight fine, and the carrier can be held liable for structural damage.

What running heavy costs

Flat brackets by excess weight (MCA 61-10-145). Up to 2,000 over $30; 2,001-4,000 $75; 4,001-6,000 $125; 6,001-8,000 $175; 8,001-10,000 $250; 10,001-12,000 $275; 12,001-14,000 $300; 14,001-16,000 $400; 16,001-18,000 $500; 18,001-20,000 $600; 20,001-25,000 $1,000; more than 25,000 over $2,000. No per-pound rate; the top bracket is a flat $2,000.

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