Idaho Truck Weight Limits

How much a truck can weigh in Idaho

The Interstate limit is 80,000 pounds (Idaho Code 49-1001). Buy an extra-length/excess-weight permit and you can run 105,500 pounds on most state and local roads, or up to 129,000 on the designated 129K route network (IDAPA 39.03.06). Fines climb fast once you pass 4,000 over. Past 20,000 over you pay $2,500 plus 30 cents a pound (Idaho Code 49-1013).

Axles, off-Interstate, and permits

• Off the Interstate: 80,000 lb base; up to 105,500 lb statewide with an extra-length/excess-weight permit, and up to 129,000 lb on the designated 129K route network
• Single axle: 20,000 lb
• Tandem axle: 34,000 lb (federal on the Interstate; Idaho allows more off-Interstate under its own weight/tire-width table)
• With a permit: 129,000 lb on designated routes (extra-length/excess-weight combinations, IDAPA 39.03.06); 105,500 lb on other state and local highways with a permit
• Idaho grandfathers 105,500-lb LCVs onto its Interstates (23 CFR 658 App. C). Off-Interstate tandem allowances run above the federal 34,000 under Idaho's axle/tire-width table; confirm the exact figure with ITD for your configuration (medium confidence on the off-Interstate tandem number).

Posted bridge and road limits

Bridges and local roads carry MUTCD 'WEIGHT LIMIT X TONS' signs. Tons are 2,000-pound short tons, so 10 TONS is 20,000 pounds. A posted limit beats your legal weight. If the sign reads 15 tons and you gross 80,000, you detour. Crossing a posted-under-capacity bridge is its own violation, and you can be billed for any damage.

What running heavy costs

Graduated by pounds over (Idaho Code 49-1013). 1-1,000 over $5; 1,001-2,000 $15; 2,001-4,000 $25; 4,001-15,000 $25 plus about $0.1341/lb over 4,000; 15,001-20,000 $1,500 plus $0.20/lb over 15,000; 20,001 and up $2,500 plus $0.30/lb over 20,000. Add $150 for failing to deploy a variable-load suspension axle that overloads adjacent axles by 2,001 lb or more.

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