| Axle | The common axis of rotation of one or more wheels whether power-driven or freely rotating, and whether in one or more segments, and regardless of the number of wheels carried thereon. |
| Axle Group | An assemblage of two or more consecutive axles considered together in determining their combined load effect on a bridge or pavement structure. |
| Automobile Transporter | Any vehicles or combination designed and used exclusively for the transport of assembled highway vehicles. |
| Bus | A motor vehicle designed primarily for the transportation of persons rather than property and having a passenger-carrying capacity of 10 or more persons, other than a taxicab constructed and designed for transporting persons for commercial purposes. |
| Cargo | The items or freight to be moved; including items placed on or in a vehicle, towed by a vehicle, or a vehicle itself. |
| Connecting Mechanism | An arrangement of parts interconnecting two or more consecutive axles to the frame of a vehicle in such a manner as to equalize the load between axles. |
| Dromedary Unit | A load carrying compartment on a truck-tractor located between the cab and the fifth wheel. |
| 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 and load-holding device thereon. |
| Length | The total longitudinal dimension of a single vehicle, a trailer, or a semi trailer. Length of a trailer or semi trailer is measured from the front of the cargo-carrying unit to its rear, exclusive of all overhang, safety or energy efficiency devices, including air conditioning units, air compressors, flexible fender extensions, splash and spray suppressant devices, bolsters, mechanical fastening devices, and hydraulic lift gates. |
| Load | A weight or quantity of anything resting upon something else regarded as its support. |
| Motor Vehicle | A vehicle which is self-propelled or propelled by electric power obtained from overhead trolley wires, but not operating upon rails. |
| Operator | Every person who drives or is in actual physical control of a motor vehicle upon a highway or who is exercising control over or steering a vehicle being towed by a motor vehicle. |
| Owner | A person, other than a lien-holder, having the property in or title to a vehicle, including a person entitled to the use and possession of a vehicle subject to a security interest in another person, but excluding a lessee under a lease not intended as security. |
| Pavement Structure | The combination of subbase, base course, and surface course placed on an earth subgrade to support the traffic load and distribute it to the roadbed. |
| Quadrum Axle | Any four consecutive axles whose extreme centers are not more than 192 inches (16 ft or 4.9 m) apart and are individually attached to or articulated from, or both, a common attachment to the vehicle including a connecting mechanism designed to equalize the load between the axles. |
| Regular Operation | The movement over highways of vehicles, vehicle combinations, and loads thereon, subject to the recommended limitations contained in this guide governing maximum weights and dimensions for motor vehicles and loads thereon. |
| Scale Tolerance | An allowable variation in the static weight of an axle load in accordance with, but not exceeding the precision of the scale involved. |
| Semi trailer | Every single vehicle without motive power designed for carrying property and so designed in conjunction and used with a motor vehicle that some part of its own weight and that of its load rests or is carried by another vehicle and having one or more load-carrying axles. |
| Single Axle | An assembly of two or more wheels whose centers are in one transverse vertical plane or may be included between two parallel transverse planes 40 inches (3.3 ft or 1.0 m) apart extending across the full width of the vehicle. |
| Special Permit | A written authorization to move or operate on a highway a vehicle or vehicles with or without a load of size and/or weight exceeding the limits prescribed for vehicles in regular operation. |
| Special Permit Applicant | An individual, firm, partnership, corporation, or association making application for a special permit to transport a vehicle, vehicles, and/or load which is oversize or overweight and under whose authority and responsibility such vehicle or load is transported. |
| Steering Axle | The axle or axles of a motor vehicle or combination of vehicles by which the same is guided or steered. |
| Stinger-Steered Automobile Transporter | A truck-tractor semi trailer combination where the fifth wheel is located on a drop frame behind and below the drive axle of the power unit. In this configuration, vehicles are carried behind or both behind and above the cab of the power unit, as well as on the semi trailer. |
| Tandem Axle | Any two axles whose centers are more than 40 inches (3.3 ft or 1.0 m) but not more than 96 inches (8 ft or 2.4 m) apart and are individually attached to or articulated from, or both, a common attachment to the vehicle including a connecting mechanism designed to equalize the load between axles. |
| Tire, Pneumatic | A tire of rubber or other resilient material which depends upon compressed air for support of a load. |
| Trailer | Every single vehicle without motive power designed for carrying property wholly on its own structure, drawn by a motor vehicle which carries no part of the weight and load of the trailer on its own wheels and having two or more load carrying axles. |
| Traveled Way | The portion of the roadway for the movement of vehicles, exclusive of shoulders and auxiliary lanes. |
| Tridum Axle | Any three consecutive axles whose extreme centers are not more than 144 inches (12 ft or 3.7 m) apart, and are individually attached to or articulated from, or both, a common attachment to the vehicle including a connecting mechanism designed to equalize the load between axles. |
| Triple Saddle Mount | A combination of four truck-tractors where the front axle of second truck-tractor is mounted on the fifth wheel of the lead truck-tractor, the front axle of the third truck-tractor is mounted on the fifth wheel of the second truck-tractor, and the front axle of the fourth truck-tractor is mounted on the fifth wheel of the third truck-tractor; and with the rear wheels of the second, third, and fourth truck-tractors trailing on the ground behind the operating motor unit. |
| Truck | A single unit motor vehicle used primarily for the transportation of property. |
| Truck Tractor | A motor vehicle used primarily for drawing other vehicles and not so constructed as to carry a load other than a part of the weight of the vehicle and load so drawn. |
| Turning Path | The path of a designated point on a vehicle making a specified turn. |
| Turning Track Width | The radial distance between the turning paths of the outside of the outer front tire and the outside of the rear tire which is nearest the center of the turn. |
| Variable Load Suspension Axles | Axles which can be regulated by the driver of the vehicle. These axles are controlled by hydraulic and air suspension systems, mechanically, or by a combination of these methods. |
| Vehicle | A device in, upon, or by which any person or property may be transported or drawn upon a highway, except devices moved by human power or used exclusively upon stationary rails or tracks. |
| Vehicle Combination | An assembly of two or more vehicles coupled together for travel upon a highway. |
| 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. |