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Questions and Answers About Vehicle Size and Weight

23 CFR 658.17 Weight

23 CFR 658.17 Weight

What is the minimum/maximum gross weight limit that States must enforce on the Interstate System?

It is 80,000 pounds, unless a lower weight is derived from the bridge formula, or a higher weight is grandfathered.

May States set weight limits on the Interstate System at less than the Federal maximum weight limits?

No. When Interstate System weight limits were raised to the current levels in 1974 (20,000 pounds single axle, 34,000 pounds tandem axle, 80,000 pounds overall gross weight limits, plus bridge formula limits), States were not required to raise their limits accordingly, although most did. However, six contiguous States in the Mississippi Valley, referred to as the "barrier States," did not and effectively limited the weight for all vehicles moving across them to their own limits. This was changed in 1982 when Congress established Interstate System weight limits as minimums as well as maximums.

Are grandfathered weights minimums?

No. States may lower grandfathered weights (but not below Federal minimum weight limits) and raise them to the grandfathered maximum at a later date if they wish.

What is the definition of a single axle?

It is one or more axles not more than 40 inches apart. If two axles are less than 40 inches apart, they are considered to be a single axle.

What is the minimum/maximum single axle weight limit that States must enforce on the Interstate System?

It is 20,000 pounds or a higher grandfathered weight.

What is the definition of a tandem axle?

It is two or more consecutive axles over 40 inches but not over 96 inches apart. If there were 3 axles within that distance, they would be considered a tandem axle for the purpose of Interstate weight limits.

What is the minimum/maximum tandem axle weight limit that States must enforce on the Interstate System?

It is 34,000 pounds or a higher grandfathered weight.

What is the bridge formula?

It is a mathematical formula designed to protect bridges by establishing a maximum weight for all groups of two or more consecutive axles on a vehicle.

Are weights derived from the bridge formula minimums as well as maximums?


What weight limit applies when the single or tandem axle, gross, or bridge formula limits result in different maximum weight limits?

Whichever is the lowest. To do otherwise would violate whatever weight limit was exceeded.

When is "rounding" appropriate?

When, for example, values are given in whole.

How are bridge formula weights determined when distances between axles are not in whole feet?

Since the bridge formula is a Federal requirement, rounding is a policy question vested in the FHWA. Since the purpose of the bridge formula is to protect bridges, the appropriate policy is to round down when the distance between axles exceeds the nearest foot by less than 6 inches. When the distance exceeds the nearest foot by 6 inches or more, a State may decide for itself whether to round up or down to the nearest foot.

As shown in the bridge formula pamphlet, may a State round 8-foot, 1-inch down to 8-foot?

No. A State may only round down to the next lower bridge formula weight limit, i.e., "more than 8 feet," since the 34,000 pound tandem axle weight limit does not apply at axle distances over 8 feet.

If a State had grandfathered weight limits in a commercial zone after 1956 and sometime later the size of the commercial zone was increased, would the higher weight limits apply in the enlarged zone?

No. Grandfather rights would continue to apply only where they applied in 1956.

Does the Secretary have authority to waive Interstate System weight limits in an emergency?

No. Federal law and regulations do not provide any authority to set aside or waive Federal weight requirements on the Interstate System. Furthermore, weight laws on the Interstate System are actually State laws. Federal law simply provides that States must adopt and enforce Federal weight laws or lose Federal highway funds. Even if Federal weight requirements were waived, State laws would still apply.

Are there any circumstances where the Secretary may waive Interstate System weight limits?

Yes. Section 1064 of the National Defense Authorization Act for Fiscal Year 2002 amended 23 U.S.C. 127 to allow the Secretary, in consultation with the Secretary of Defense, to waive the Interstate System weight limit on I-95 between Augusta and Bangor, Maine, for bulk shipments of jet fuel to the Air National Guard at Bangor International Airport in an emergency. Generally, however, Congress has not provided authority for waivers but has statutorily established either specific higher weight limits or grandfather dates that do so.

What are grandfather rights?

They arise from 23 U.S.C. 127(a) and allow State weight limits to exceed normal Federal weight limits on the Interstate System. Under the first grandfather right, a State may allow vehicles to operate at higher than normal single axle, tandem axle, and/or gross weight limits if such weights were permitted on its public highways on July 1, 1956. Under the second grandfather right, a State may allow vehicles to operate at higher than normal bridge formula or axle spacing weight limits if such weights were permitted on its public highways on January 4, 1975. Exceptions: the date of all grandfather rights for Michigan is May 1, 1982; for Maryland June 1, 1993; and for the first grandfather right in Hawaii, February 1, 1960.

Where do grandfather weights apply?

They apply only on the Interstate System and routes providing reasonable access between it and terminals and facilities for food, fuel, repairs and rest.

May States that reduce grandfather weights subsequently raise them?

Yes. Grandfather weights are vested on the date specified by Congress and are not affected even if a State chooses to adopt a lower limit for some period of time. States may not reduce grandfather weights below normal Interstate weight limits.

What is the significance of a vehicle or cargo being nondivisible?

States may issue permits for nondivisible vehicles or loads to exceed Interstate System weight limits or ISTEA freeze length limits.

May States issue nondivisible overlength permits for vehicles or cargo to exceed the maximum length of the cargo-carrying units of vehicles with two or more such units imposed by the ISTEA freeze?

Yes, although as a practical matter, they will rarely be needed since they would usually apply only on loads, such as buildings, that are moved on a series of dollies, each of which is a single cargo-carrying unit, or long loads such as rockets that would require two overlength cargo-carrying units (States would be free to regulate the length of front and rear overhangs, if any).

On what highways does the Federal definition of nondivisible apply?

(1) For nondivisible overweight vehicles or loads, the Interstate System and highways providing reasonable access to and from it. (2) For combinations with 2 or more cargo carrying units subject to the ISTEA freeze on length, highways shown in Appendix C to 23 CFR 658.

If a vehicle or load cannot be dismantled in 8 hours using appropriate equipment, must it be dismantled to whatever extent is possible in 8 hours?

No. If a vehicle or load cannot be dismantled in 8 hours, it is nondivisible and a State may issue a nondivisible overweight permit. However, if parts are removed to facilitate transportation of an overweight load, they cannot be loaded on the same vehicle.

Are some vehicles and articles defined by regulation as nondivisible?

Yes. States may treat emergency response vehicles, such as firetrucks used to protect persons and property from fires and other disasters that threaten public safety (but not trucks carrying relief supplies), casks designed for the transport of spent nuclear materials and vehicles carrying marked military materiel as nondivisible vehicles or loads. Vehicles under lease or contract to the military would not qualify as nondivisible.

May States consider intermodal shipping containers to be nondivisible?

States may consider containers moving in international commerce as nondivisible but are not required to do so.

Does the 8-hour rule in the definition of nondivisible vehicles or loads include reassembly time?

No. It includes only disassembly time.

Does the 8-hour rule in the definition of nondivisible vehicles or loads include the labor of one or more persons?

It means 8 person hours, i.e., 8 hours for one person, 4 hours apiece for two persons, or 2 hours apiece for 4 persons.

If a blade must be removed from a bulldozer because it is overwidth even though the removal takes more than eight hours, may the blade and power unit be considered a nondivisible load?

No. It is not nondivisible if it has already been divided.

Is a concrete pumper truck carrying water in a tank and lengths of pipe, both necessary to the pumping operation, nondivisible?

No. The water is infinitely divisible and could be carried to the site in another vehicle, as could the pipe.

Do SPREAD OR SPLIT TANDEMS (Two consecutive axles more than 96 inches apart.) axles qualify for the exception to the bridge formula that allows two consecutive sets of tandem axles between 36 and 38 feet apart to carry 68,000 pounds?

No. The exception applies only for tandem axles more than 40 inches but not over 96 inches apart.

May States limit the maximum weight of steering axles on the Interstate System to less than 20,000 pounds?

They may limit the weight to 20,000 pounds or the axle weight rating established by the manufacturer, whichever is lower.

May States limit the weight per inch of tire or tread widths?

States may limit tire loads on the Interstate System, but not to less than 500 pounds per inch of tire or tread widths. Tire load limits may not be applied to steering axles.

May States allow vehicle weight tolerances above Interstate System weight limits?

No. Federal law specifically prohibits this. All Interstate weight limits must include all enforcement tolerances.

May VARIABLE LOAD SUSPENSION, BOOSTER, CHEATER, DUMMY OR TAG axles be included in determining maximum weight limits under the Federal Bridge Formula on the Interstate System?

Each State may determine for itself whether or not to do so. Some States require that such axles carry a minimum amount of weight or that the control be outside the cab in order to be counted as an axle under the bridge formula.
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