A-dolly: A converter dolly that is towed from a single hitch at the center line of the tow vehicle and contains the lower half of the fifth wheel assembly that when connected by kingpin to a semi-trailer converts the combined configuration into a full trailer.

A-train double: A combination of vehicles composed of a tractor, a semi-trailer and either an A-dolly and a semi-trailer or a full trailer attached to the rear of the forward semi-trailer as if an A-dolly were used.

Axle: The common axis of rotation of one or more wheels, either power-driven or freely rotating, in one or more segments in the same transverse plan. (Expanded from the definition in chapter 46.04.060 RCW.)

Axle group: Any set of two or more parallel axles associated with a single vehicle or vehicle combination.

Axle group weight: The part of the gross vehicle weight transmitted to the highway by the defined axle group.

Axle spacing (spread): The longitudinal distance between the centers of the foremost and rearmost axles of an axle group measured from center to center of the defined axles.

B-train double: A combination of vehicles composed of a tractor, a semi-trailer and a second semi-trailer connected by kingpin to the lower half of a fifth wheel assembly mounted on the rear of the forward semi-trailer.

C-dolly: A converter dolly that is equipped with a single axle that is self-steering, towed from two hitches located in a horizontal transverse line on the towing unit, and is so designed that when the trailer converter dolly is coupled to a towing trailer, the trailer converter dolly cannot pivot horizontally with respect to the towing trailer.

Axle spacing report: A report stating the maximum amount of weight a vehicle, or vehicle combination, can carry, both legally and under permit, based on the number of axles, the axle spacings, and the number and sizes of tires on the vehicle, or vehicle combination.

Combination length: The total length of a combination of vehicles, i.e., truck-tractor—semi-trailer—trailer combination, measured from front extremity of the first vehicle to the rear extremity of the last vehicle, including the connecting space between vehicles and any overhanging load.

Combined trailer length: The total length of a combination of trailers measured from the front extremity of the first trailer to the rear extremity of the last trailer including the connecting space and any overhanging load.

Converter dolly: A vehicle unit that is designed, usually with the bottom half of a fifth wheel assembly, to convert a semi-trailer with kingpin into a full trailer.

C-train double: A combination of vehicles composed of a tractor, a semi-trailer, a C-dolly and a second semi-trailer.

Daylight hours: One-half hour before sunrise until one-half hour after sunset.

Extra-legal vehicle: A vehicle, laden or unladen, which exceeds legal dimensions and/or weights and operates on highways by permit.

Gross weight: The weight of a vehicle and/or combination of vehicles plus the weight of any load thereon.

Height: The total vertical dimension of a vehicle above the ground surface including any load or appurtenance.

Length: The total longitudinal dimension of a single vehicle, vehicle combination (see combination length), or individual trailer or semi-trailer. Trailer length is measured from the front of the cargo-carrying unit to its rear, exclusive of all overhangs from safety or energy efficiency devices (see also measurement exclusive devices). Length of a loaded trailer must include any overhangs of load when determining compliance with length limits or the need for a special permit.

Longer combination vehicle: A combination of truck tractor, semi-trailer, and trailer that exceeds legal length dimensions and operates on highways by permit for transporting reducible loads.

Maximum off track: The maximum difference in the path created by the center of the steering axle and the center of the rearmost axle of the vehicle or vehicle combination during the negotiation of a turn.

Multilane highway: A highway with two or more lanes of travel in the same direction.

Measurement exclusive devices: Certain devices that provide added safety, energy conservation, or are otherwise necessary, and are not designed to carry cargo.

National network: Those interstate and other federal-aid primary highways on which commercial vehicles of the dimensions authorized by the Surface Transportation Assistance Act of 1982 are allowed to operate.

Night: Night means one-half hour after sunset to one-half hour before sunrise.

Nondivisible load: A load that cannot be readily or reasonably dismantled and is reduced to a minimum practical size and weight. Portions of a load can be detached and reloaded on the same hauling unit when the separate pieces are necessary to the operation of the machine or equipment which is being hauled: Provided, That the arrangement does not exceed permit limits for the configuration without the reloaded pieces. The federal definition of nondivisible load to be used for vehicles operating on the interstate is as follows: Any load or vehicle exceeding applicable length or weight limits that, if separated into smaller loads or vehicles, would: Compromise the intended use of the vehicle, destroy the value of the load or vehicle, require more than eight work hours to dismantle using appropriate equipment.

Permit: A written or electronic authorization to:

(a) Move or operate a vehicle, or combination of vehicles, on a highway;

(b) With or without a load;

(c) Of size and/or weight exceeding the limits prescribed for vehicles in regular operation.

Pilot/escort vehicle: A motor vehicle used for the express purpose as a warning and guide vehicle for extra-legal vehicles.

Pounds per inch of tire width: A measure of load restriction based on rated tire size. The pounds per inch of tire width are determined by dividing the weight carried on the axle group by the number of tires in the group and dividing again by the manufacturer's rated tire width as indicated on the sidewall of the tire.

Rear overhang: The distance from the center of the last axle to the end of the load, or portion of the vehicle whichever is longer.

Regional permit: Permits issued for interstate movement of certain nondivisible overweight and/or oversize vehicles and/or loads on highways designated by the jurisdictions participating in the "Western Regional Agreement for the Issuance of Permits for Overweight and/or Oversize Vehicles and/or Loads Involved in Interstate Travel."

Regular operation: The movement over highways of motor vehicles with dimensions and weights specified by state and federal codes.

Retractable axle: An axle that can be separately raised and lowered by the driver of the vehicle but may not have its weight bearing capacity regulated from within reach of the driver's compartment. Also known as "lift axle" and "booster axle," or more formally known as a "variable load suspension" (VLS) axle.

Rocky mountain double: A combination of vehicles including a truck-tractor pulling a long semi-trailer and a shorter trailer.

Single axle: An assembly of two or more wheels whose centers are in one transverse vertical plane and which are transmitting weight to the highway.

Single unit: A motor vehicle with no attached vehicles, i.e., truck, bus, truck-tractor.

Steering axle: The axle or axles on the front of a motor vehicle that are activated by the operator to directly accomplish guidance or steerage of the vehicle and/or a combination of vehicles.

Superload: A superload is any load that would require special analysis and approval by one or more state permit offices because of dimensions or weight. Criteria for superloads in Washington state are found in WAC 468-38-405.

Tandem axle: Any two consecutive single axles whose centers may be included between parallel transverse vertical planes spaced at least four feet but not more than eight feet apart, extending across the width of the vehicle, articulating from a common attachment, or designed to automatically equalize the load between the two axles. This working definition is extrapolated from RCW 46.44.041.

Tote: Common term for a motor vehicle used to transport manufactured housing.

Tridem axle: Any three consecutive single axles whose extreme centers may be included between parallel transverse vertical planes spaced not more than twelve feet apart, extending across the width of the vehicle, and are articulated from a common attachment to the vehicle, or are designed to automatically equalize the load between the three axles.

Truck-tractor: A motor vehicle used primarily for pulling other vehicles but not specifically constructed to carry a load other than a part of the weight of the vehicle and load being pulled. This vehicle may include a small freight compartment (also referred to as a dromedary box), deck or plate not more than eight feet in length used for carrying a load. Federal rule allows the interstate use of a vehicle with a dromedary box only if the vehicle was in operation prior to December 1, 1982, proof to be provided by the vehicle operator. This working definition was extrapolated from RCW 46.04.655, 46.44.037 and Code of Federal Regulation, 23 C.F.R. 658.13(f).

Trunnion axle: An axle configuration with two individual axles mounted in the same transverse plane, with four tires on each axle, connected at a pivot point that allows each individual axle to oscillate in a vertical plane to provide constant and equal weight distribution on each individual axle.

Trunnion axle group: Two or more consecutive trunnion axles, that are individually attached to, and/or articulated from, the vehicle, and may include a weight equalizing suspension system.

Turnpike double: A combination of vehicles including a truck-tractor pulling a long semi-trailer and an additional long trailer.

Wide base tire: A tire whose nominal section (sidewall to sidewall) width, as identified by tire nomenclature, is over fourteen inches.

Width: The total outside transverse dimension of a vehicle including any load or load-holding devices thereon, but excluding approved safety devices and tire bulge due to load.