A dolly is an unpowered vehicle designed for connection to a

tractor unit A tractor unit (also known as a truck unit, power unit, prime mover, ten-wheeler, semi-tractor, tractor truck, semi-truck, tractor cab, truck cab, tractor rig, truck rig or big rig or simply a tractor, truck, semi or rig) is a characteristical ...

truck A truck or lorry is a motor vehicle designed to transport cargo, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame construction ...

or prime mover vehicle with strong traction power.

United States

Classification by axle configuration

There are several types of dolly

bogie A bogie ( ) (in some senses called a truck in North American English) is a chassis or framework that carries a wheelset, attached to a vehicle—a modular subassembly of wheels and axles. Bogies take various forms in various modes of transp ...

: * Full trailer - 2 axle (4 wheels), with a

draw bar A drawbar is a solid coupling between a hauling vehicle and its hauled load. Drawbars are in common use with rail transport, road trailers, both large and small, industrial and recreational, and with agricultural equipment. Agriculture and ...

which also controls the trailer's front axle steering. The draw bar does not take load of the full trailer. Heavy full trailer needs to have its own brakes remotely controlled by the prime mover vehicle. *

Semi-trailer A semi-trailer is a trailer without a front axle. In the United States, the term is also used to refer to the combination of a truck and a semi-trailer; a tractor-trailer. A large proportion of a semi-trailer's weight is supported by a tracto ...

- 1 axle (2 wheels), without the front axle but have a landing gear. Large semi-trailer of truck size is designed for connection via the

fifth wheel The fifth-wheel coupling provides the link between a semi-trailer and the towing truck, tractor unit, leading trailer or dolly. The coupling consists of a kingpin, a vertical steel pin protruding from the bottom of the front of the semi-tr ...

on the

or the

semi-trailer truck A semi-trailer truck, also known as a semitruck, (or semi, eighteen-wheeler, big rig, tractor-trailer or, by synecdoche, a semitrailer) is the combination of a tractor unit and one or more semi-trailers to carry freight. A semi-trailer ...

. Small semi-trailer such as

travel trailer A caravan, travel trailer, camper, tourer or camper trailer is a trailer towed behind a road vehicle to provide a place to sleep which is more comfortable and protected than a tent (although there are fold-down trailer tents). It provides the ...

and

boat trailer A boat trailer is designed to launch, retrieve, carry and sometimes store boats. Commercial boat trailers Commercial hydraulic boat trailers are used by marinas, boat yards, boat haulers, boat dealers and boat builders. Generally this type ...

is designed for connection via a

tow hitch A tow hitch (or tow bar or trailer hitch in North America) is a device attached to the chassis of a vehicle for towing, or a towbar to an aircraft nose gear. It can take the form of a tow ball to allow swiveling and articulation of a trailer, ...

of a passenger vehicle. Either the fifth wheel or the tow hitch takes up to half the load of the semi-trailer. *

Road train A road train, land train or long combination vehicle (LCV) is a trucking vehicle used to move road freight more efficiently than semi-trailer trucks. It consists of two or more trailers or semi-trailers hauled by a prime mover. History Early ...

- special large dolly

equipped with a

for further connection by the gooseneck type drawbar of another similar dolly and form a

road train A road train, land train or long combination vehicle (LCV) is a trucking vehicle used to move road freight more efficiently than semi-trailer trucks. It consists of two or more trailers or semi-trailers hauled by a prime mover. History Early ...

. The last dolly in a road train needs its own rear lights, brakes remotely controlled by the prime mover vehicle, and

registration plate A vehicle registration plate, also known as a number plate (British English), license plate (American English), or licence plate ( Canadian English), is a metal or plastic plate attached to a motor vehicle or trailer for official identificat ...

. * Tow dolly - a

semi-trailer A semi-trailer is a trailer without a front axle. In the United States, the term is also used to refer to the combination of a truck and a semi-trailer; a tractor-trailer. A large proportion of a semi-trailer's weight is supported by a tracto ...

designed as automobile rescue equipment. It is designed to couple to the concerned automobile's powered wheel, i.e. the front wheel of a

Front-wheel drive Front-wheel drive (FWD) is a form of engine and transmission layout used in motor vehicles, where the engine drives the front wheels only. Most modern front-wheel drive vehicles feature a transverse engine, rather than the conventional longit ...

automobile, or the rear wheel of a rear-wheel drive automobile, by locking the powered wheels onto the tow dolly's tray. The tow dolly is

connected to a

tractor A tractor is an engineering vehicle specifically designed to deliver a high tractive effort (or torque) at slow speeds, for the purposes of hauling a trailer or machinery such as that used in agriculture, mining or construction. Most common ...

. Tow dollies are legal in all 50 US states and Canada. In the U.S. and Canada brakes are required on any loaded car tow dolly.

Classification by coupling configuration

There are two basic types: * ''Converter dolly'', equipped with between one and three axles and designed to connect to a towbar on the rear of the truck or trailer in front. There are two variants of this: ** An ''A-dolly'' has a single drawbar with a centred coupling. ** A ''C-dolly'' has two separate couplings side-by-side. * ''

Low loader A lowboy (low-loader in British English, low-bed in western Canada and South Africa or float in Australia and eastern Canada) is a semi-trailer with two drops in deck height: one right after the gooseneck and one right before the wheels. This all ...

'' dolly, equipped with a ''gooseneck'' type drawbar that attaches to the

fifth wheel coupling Fifth is the ordinal form of the number five. Fifth or The Fifth may refer to: * Fifth Amendment to the United States Constitution, as in the expression "pleading the Fifth" * Fifth column, a political term * Fifth disease, a contagious rash tha ...

on the rear of a

prime mover Prime mover may refer to: Philosophy *Unmoved mover, a concept in Aristotle's writings Engineering * Prime mover (engine), motor, a machine that converts various other forms of energy (chemical, electrical, fluid pressure/flow, etc) into energy ...

to distribute the mass on the fifth wheel on the dolly between the prime mover and the wheels of the dolly. These are predominantly fitted with two axles.

Australia

Converter dollies are used in

s in

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

, most commonly with two or three axles and a hinged drawbar. They are also frequently referred to as ''road train dollies''. The C-dolly design is not allowed in Australia, as it prevents articulation between the dolly wheels and the axles of the truck or trailer in front of the dolly. Australian rules require articulation between axle groups. Low-loader dollies – which present a kingpin rather than a drawbar coupling – are used with many

low loader A lowboy (low-loader in British English, low-bed in western Canada and South Africa or float in Australia and eastern Canada) is a semi-trailer with two drops in deck height: one right after the gooseneck and one right before the wheels. This all ...

s to allow heavy cargo to be carried without overloading the wheels of the prime mover or the low loader.

Airport dolly

Dollies are used for the transportation of loose

baggage Baggage or luggage consists of bags, cases, and containers which hold a traveler's personal articles while the traveler is in transit. A modern traveler can be expected to have packages containing clothing, toiletries, small possessions, trip ...

s, oversized bags,

mail The mail or post is a system for physically transporting postcards, letter (message), letters, and parcel (package), parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid ...

bags, loose cargo carton boxes, etc. between an aircraft and the terminal or sorting facility. In the US, these dollies are called baggage carts, but in Europe

baggage cart Baggage carts, luggage carts, luggage trolleys or trolleys are small vehicles pushed by travelers ( human-powered) to carry individual luggage, mostly suitcases. There are two major sizes: One for big luggage and one for small luggage. Carts h ...

means baggage trolleys used by individual passengers.

References

{{Reflist

External links

Diagrams of A-dolly & C-dolly.

Evaluation of dollies, University of Michigan

Legal definition of a dolly
in

Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...

USA The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

Images of trailer dollies
Trucks