Weight requirements

Scope

These regulations apply to all users of the National System of Interstate and Defense Highways and the reasonable access thereto.

Regulatory citations

• 23 CFR 658.17 — Weight

Key definitions

• Interstate system: The National System of Interstate and Defense Highways described in sections 103(e) and 139(a) of Title 23, U.S.C. For the purpose of this regulation this system includes toll roads designated as Interstate.
• National Network (NN): The composite of the individual network of highways from each state on which vehicles authorized by the provisions of the Surface Transportation Assistance Act of 1982 (STAA) are allowed to operate. The network in each state includes the Interstate System. The National network is set out by the Federal Highway Administration (FHWA) in 23 CFR 658, Appendix A.

• Nondivisible load or vehicle: Any load or vehicle exceeding applicable length or weight limits which, if separated into smaller loads or vehicles, would:
  • Compromise the intended use of the vehicle, i.e., make it unable to perform the function for which it was intended;
  • Destroy the value of the load or vehicle, i.e., make it unusable for its intended purpose; or
  • Require more than eight workhours to dismantle using appropriate equipment. The applicant for a nondivisible load permit has the burden of proof as to the number of workhours required to dismantle the load.

Summary of requirements

The maximum gross weights are limited to:

• 80,000 pounds on any vehicle except where lower gross vehicle weight is dictated by the bridge formula;
• 20,000 pounds on any one axle; and
• 34,000 pounds on tandem axles.

Vehicles and vehicle combinations are not allowed on Interstate highways if the gross weight on two or more consecutive axles exceeds the limitations prescribed in the Bridge Gross Weight Formula.

This formula limits the weight on groups of axles to reduce the risk of damage to highway bridges. Allowable weight depends on the number of axles a vehicle has and the distance between those axles. However, the single- or tandem-axle weight limits supersede the Bridge Formula limits for all axles not more than 96 inches apart.

States cannot limit tire loads to less than 500 pounds per inch of tire or tread width, except that such limits may not be applied to tires on the steering axle. They also can not limit steering axle weights to less than 20,000 pounds or the axle rating established by the manufacturer, whichever is lower.

States may issue special permits without regard to the axle, gross, or Federal Bridge Formula requirements for nondivisible vehicles or loads.

Exceptions. Two consecutive sets of tandem axles can carry a gross load of 34,000 pounds each if the overall distance between the first and last axle is 36 feet or more. In any case, the total gross weight of a vehicle cannot exceed 80,000 pounds.

Any vehicle that uses an auxiliary power unit (APU) or idle reduction technology unit in order to promote reduction of fuel use and emissions because of engine idling, may be allowed up to an additional 400 pounds total in gross, axle, tandem, or bridge formula weight limits. To be eligible for this exception, the vehicle operator must be able to prove by written certification, the weight of the APU, and by demonstration or certification that the idle reduction technology is fully functional at all times. Each state must adopt a regulation regarding the APU weight exemption before it can be used.

The Fixing America’s Surface Transportation Act (FAST Act) enacted in December of 2015 allowed additional exceptions. Moving Ahead for Progress in the 21st Century Act (MAP-21) further increased the weight allowance for idle reduction technology including APUs. Section 127 of Title 23 of the United States Code has been updated to reflect the changes; however, 23 CFR 658.17 has not yet been updated.

Additionally, be aware that all states have not incorporated the provisions in to their state’s statutes or regulations. Check the applicable state regulations for more information.

Under the provisions of the FAST Act and MAP-21:

• Bulk milk is considered nondivisible. States may issue permits for milk haulers to exceed 80,000 pounds or the Federal Bridge Formula.
• A vehicle with an engine fueled primarily by natural gas may exceed any vehicle weight limit on a single axle, tandem axle, and bridge formula weights by an amount that is equal to the difference between the weight of the vehicle attributable to the natural gas tank and fueling system carried by that vehicle and the weight of a comparable diesel tank and fueling system (up to a maximum gross vehicle weight of 82,000 pounds).
• Idle reduction technology or auxiliary power units (APU) allowed up to 550 pounds with the conditions above to use the exception remain in place.