Truck Weight Limits and Axle Rules Explained

Overweight violations are among the most expensive routine penalties in trucking. Fines scale dramatically with how much over the legal limit a vehicle is, and in some jurisdictions repeat overweight violations can result in permit revocation or operating restrictions. Understanding how weight limits actually work — not just the headline 80,000 lb number, but the axle distribution rules that determine legality in practice — is essential for every owner-operator and fleet operator.

The 80,000 lb Federal Limit (USA)

The Federal Highway Administration (FHWA) sets the maximum gross vehicle weight (GVW) for vehicles operating on the Interstate Highway System at 80,000 lbs (approximately 36,287 kg). This is the most cited number in trucking, but it is not the only number that matters. A truck can be well under 80,000 lbs gross and still be in violation if the weight is not properly distributed across its axles.

The federal weight limits under 23 USC 127 establish three separate constraints that must all be satisfied simultaneously:

• Single axle: 20,000 lbs maximum
• Tandem axle group (two axles within 40 inches to 96 inches of each other): 34,000 lbs maximum
• Gross vehicle weight: 80,000 lbs maximum, subject to the federal bridge formula

States have authority to set their own limits on non-Interstate roads, and many do — particularly for spring weight restrictions. However, no state can permit a weight on an Interstate that exceeds the federal limits unless the vehicle qualifies for a special permit.

The Federal Bridge Formula

The bridge formula (also called Bridge Formula B) is a mathematical limit designed to prevent trucks from concentrating too much weight over a short section of pavement or bridge. It limits the weight that can be carried based on the number of axles and the distance between the outermost axles of a group.

The formula is: W = 500 [(LN/(N-1)) + 12N + 36], where W is the maximum weight in pounds, L is the distance in feet between the outer axles of any group of two or more consecutive axles, and N is the number of axles in the group. The practical result is that a standard 5-axle 18-wheeler (3 axle groups on the tractor, 2 on the trailer) can carry 80,000 lbs gross only when the axle spacing is sufficient to distribute that weight within the formula limits. Trucks with shorter wheelbase configurations may be limited to less than 80,000 lbs even if each individual axle group is under its limit.

Axle Weight Management in Practice

Managing axle weights is a hands-on skill. The two primary adjustment tools available to most drivers are the sliding fifth wheel and the sliding tandems on the trailer.

Sliding tandems allow the trailer's rear axle group to slide forward or backward within the trailer frame. Moving the tandems forward shifts weight from the trailer axles toward the drive axles; moving them back shifts weight toward the trailer axles and reduces drive axle weight. The pins lock into holes spaced at set intervals (typically 4 inches apart), and each position change moves a calculable amount of weight.

Sliding fifth wheel affects the weight distribution between the steer axle and the drive axles. Moving the fifth wheel forward (toward the cab) puts more weight on the steer axle; moving it back reduces steer axle weight and increases drive axle loading. Steer axle legal limits (typically 12,000–13,280 lbs depending on tire and axle type) are commonly an issue with heavy, dense freight loaded near the front of the trailer.

Before leaving a shipper, weigh at a certified scale if there is any question about load distribution. Many truck stops have CAT scales that produce a certified weight ticket showing individual axle group weights, not just gross. A $15 scale ticket before you hit the highway is far cheaper than a $5,000 overweight fine on the scale at the port of entry.

Canadian Provincial Weight Rules

Canada does not have a single national weight standard equivalent to the US federal limit. Weight regulations are provincial — set by each province under its highway traffic act — and they vary significantly. The federal government establishes maximum weights for federally regulated carriers under the Motor Vehicle Transport Act, but enforcement and specific limits are a provincial responsibility.

General provincial maximums for a standard 5-axle tractor-trailer range from approximately 62,500 kg (British Columbia and Alberta on most highways) to higher limits in some corridors under provincial agreements. Ontario allows up to 62,500 kg on designated highways for standard configurations. Quebec has specific rules for multi-axle combinations that can permit higher gross weights with additional axles. The Prairie provinces (Manitoba, Saskatchewan, Alberta) have inter-provincial agreements allowing consistent treatment on major trade corridors.

Spring weight restrictions are a significant seasonal factor in Canadian provinces. During spring thaw — typically March through May depending on location — provinces reduce allowable weights on secondary highways (and sometimes primary highways) to protect road surfaces damaged by freeze-thaw cycles. Violating spring weight restrictions in Ontario or Quebec carries heavy fines and the violations affect your CVOR (Commercial Vehicle Operator's Registration) record.

Overweight Permits

Loads that genuinely cannot be reduced to legal weight — construction equipment, transformers, industrial machinery — can move legally under overweight/oversize permits issued by each state or province. Permits specify a route, travel times (often restricted to daylight and non-holiday periods), and may require escorts or pilot vehicles. The permit must be in the cab and available for inspection.

Permits are issued per trip or on an annual basis for recurring moves. The cost and complexity of obtaining permits scales with how far over legal limits the load is. Carriers who regularly handle oversize/overweight freight should build permit procurement lead time into their scheduling — some jurisdictions require several business days or longer for non-routine loads.

Operating overweight without a permit when one is required is a serious violation. It is not treated as a routine overweight ticket; it is treated as an unpermitted oversize/overweight move, with penalties that can include vehicle impoundment until the load is redistributed or reduced.

Scaling and Enforcement

Weigh stations on Interstate highways and major US & Canadian highways use static scales, weigh-in-motion (WIM) sensors, and portable scales for roadside inspections. WIM sensors embedded in the highway can flag vehicles for secondary inspection before they reach the scale house. If your truck is flagged and pulled in, the static scale result is the enforcement weight. Bypass systems (PrePass in the USA, SURPASS in Canada) allow compliant carriers with good safety records to bypass weigh stations electronically — a meaningful operational advantage for carriers who maintain clean records.

Stay legal on weight and keep your loads moving. Get dispatched with TRUCC — carrier-side dispatch across Canada and the USA.