What is the maximum legal weight for a combination vehicle (tractor-trailer) on Interstate highways under federal regulations?

FEDERAL WEIGHT LIMITS (23 USC 127 and 49 CFR 658): GROSS VEHICLE WEIGHT (GVW): 80,000 lbs maximum on Interstate highways. SINGLE AXLE: 20,000 lbs maximum. TANDEM AXLE (two axles within 40 inches of each other): 34,000 lbs maximum. BRIDGE FORMULA (Federal Bridge Gross Weight Formula): The weight any group of axles can carry is also limited by their axle spacing to protect bridges — the farther apart axles are, the higher the allowable weight. Even if you're under the 80,000 lb limit, you can still be overweight if axle spacing is wrong. PRACTICAL OPERATION: An 80,000 lb combination typically has a 12,000 lb steering axle, two drive axles at 34,000 lbs total, and a trailer axle at 34,000 lbs (total: 80,000 lbs). Overloading causes: tire failure from overheating; brake failure from excessive stopping demands; bridge and pavement damage; federal and state fines; liability for resulting accidents. STATE OVERSIZE/OVERWEIGHT PERMITS: Some states allow heavier loads on non-federal roads with permits (100,000-200,000+ lbs for special loads). These require route surveys, pilot vehicles, and travel restrictions. SCALE HOUSES: All states operate weigh stations requiring CMV compliance. Bypassing an open scale is a violation. Pre-clearance programs (PrePass) allow compliant carriers to bypass on some routes.