49 USC 31111 - Length limitations

(a) Definitions.— 
In this section, the following definitions apply:
(1) Automobile transporter.— 
The term automobile transporter means any vehicle combination designed and used specifically for the transport of assembled highway vehicles, including truck camper units.
(2) Maxi-cube vehicle.— 
The term maxi-cube vehicle means a truck tractor combined with a semitrailer and a separable property-carrying unit designed to be loaded and unloaded through the semitrailer, with the length of the separable property-carrying unit being not more than 34 feet and the length of the vehicle combination being not more than 65 feet.
(3) Truck tractor.— 
The term truck tractor means

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(A) a non-property-carrying power unit that operates in combination with a semitrailer or trailer; or
(B) a power unit that carries as property only motor vehicles when operating in combination with a semitrailer in transporting motor vehicles.
(4) Drive-away saddlemount with fullmount vehicle transporter combination.— 
The term drive-away saddlemount with fullmount vehicle transporter combination means a vehicle combination designed and specifically used to tow up to 3 trucks or truck tractors, each connected by a saddle to the frame or fifth-wheel of the forward vehicle of the truck or truck tractor in front of it.
(b) General Limitations.— 

(1) Except as provided in this section, a State may not prescribe or enforce a regulation of commerce that
(A) imposes a vehicle length limitation of less than 45 feet on a bus, of less than 48 feet on a semitrailer operating in a truck tractor-semitrailer combination, or of less than 28 feet on a semitrailer or trailer operating in a truck tractor-semitrailer-trailer combination, on any segment of the Dwight D. Eisenhower System of Interstate and Defense Highways (except a segment exempted under subsection (f) of this section) and those classes of qualifying Federal-aid Primary System highways designated by the Secretary of Transportation under subsection (e) of this section;
(B) imposes an overall length limitation on a commercial motor vehicle operating in a truck tractor-semitrailer or truck tractor-semitrailer-trailer combination;
(C) has the effect of prohibiting the use of a semitrailer or trailer of the same dimensions as those that were in actual and lawful use in that State on December 1, 1982;
(D) imposes a vehicle length limitation of not less than or more than 97 feet on a driveaway saddlemount with fullmount vehicle transporter combinations;
(E) has the effect of prohibiting the use of an existing semitrailer or trailer, of not more than 28.5 feet in length, in a truck tractor-semitrailer-trailer combination if the semitrailer or trailer was operating lawfully on December 1, 1982, within a 65-foot overall length limit in any State; or

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(F) imposes a limitation of less than 46 feet on the distance from the kingpin to the center of the rear axle on trailers used exclusively or primarily in connection with motorsports competition events.
(2) A length limitation prescribed or enforced by a State under paragraph (1)(A) of this subsection applies only to a semitrailer or trailer and not to a truck tractor.
(c) Maxi-Cube and Vehicle Combination Limitations.— 
A State may not prohibit a maxi-cube vehicle or a commercial motor vehicle combination consisting of a truck tractor and 2 trailing units on any segment of the Dwight D. Eisenhower System of Interstate and Defense Highways (except a segment exempted under subsection (f) of this section) and those classes of qualifying Federal-aid Primary System highways designated by the Secretary under subsection (e) of this section.
(d) Exclusion of Safety and Energy Conservation Devices.— 
Length calculated under this section does not include a safety or energy conservation device the Secretary decides is necessary for safe and efficient operation of a commercial motor vehicle. However, such a device may not have by its design or use the ability to carry cargo.
(e) Qualifying Highways.— 
The Secretary by regulation shall designate as qualifying Federal-aid Primary System highways those highways of the Federal-aid Primary System in existence on June 1, 1991, that can accommodate safely the applicable vehicle lengths provided in this section.
(f) Exemptions.— 

(1) If the chief executive officer of a State, after consulting under paragraph (2) of this subsection, decides a segment of the Dwight D. Eisenhower System of Interstate and Defense Highways is not capable of safely accommodating a commercial motor vehicle having a length described in subsection (b)(1)(A) of this section or the motor vehicle combination described in subsection (c) of this section, the chief executive officer may notify the Secretary of that decision and request the Secretary to exempt that segment from either or both provisions.
(2) Before making a decision under paragraph (1) of this subsection, the chief executive officer shall consult with units of local government in the State in which the segment of the Dwight D. Eisenhower System of Interstate and Defense Highways is located and with the chief executive officer of any adjacent State that may be directly affected by the exemption. As part of the consultations, consideration shall be given to any potential alternative route that serves the area in which the segment is located and can safely accommodate a commercial motor vehicle having a length described in subsection (b)(1)(A) of this section or the motor vehicle combination described in subsection (c) of this section.
(3) A chief executive officers notification under this subsection must include specific evidence of safety problems supporting the officers decision and the results of consultations about alternative routes.
(4) 
(A) If the Secretary decides, on request of a chief executive officer or on the Secretarys own initiative, a segment of the Dwight D. Eisenhower System of Interstate and Defense Highways is not capable of safely accommodating a commercial motor vehicle having a length described in subsection (b)(1)(A) of this section or the motor vehicle combination described in subsection (c) of this section, the Secretary shall exempt the segment from either or both of those provisions. Before making a decision under this paragraph, the Secretary shall consider any possible alternative route that serves the area in which the segment is located.
(B) The Secretary shall make a decision about a specific segment not later than 120 days after the date of receipt of notification from a chief executive officer under paragraph (1) of this subsection or the date on which the Secretary initiates action under subparagraph (A) of this paragraph, whichever is applicable. If the Secretary finds the decision will not be made in time, the Secretary immediately shall notify Congress, giving the reasons for the delay, information about the resources assigned, and the projected date for the decision.
(C) Before making a decision, the Secretary shall give an interested person notice and an opportunity for comment. If the Secretary exempts a segment under this subsection before the final regulations under subsection (e) of this section are prescribed, the Secretary shall include the exemption as part of the final regulations. If the Secretary exempts the segment after the final regulations are prescribed, the Secretary shall publish the exemption as an amendment to the final regulations.
(g) Accommodating Specialized Equipment.— 
In prescribing regulations to carry out this section, the Secretary may make decisions necessary to accommodate specialized equipment, including automobile and vessel transporters and maxi-cube vehicles.