A dolly is an unpowered vehicle designed for connection to a

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

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

or prime mover vehicle with strong traction power.

United States

Classification by axle configuration

There are several types of dolly

bogie A bogie ( ) (or truck in North American English) comprises two or more Wheelset (rail transport), wheelsets (two Railroad wheel, wheels on an axle), in a frame, attached under a vehicle by a pivot. Bogies take various forms in various modes ...

: * Full trailer – 2 axles (4 wheels), with a draw bar 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 (vehicle), trailer without a front axle. The combination of a semi-trailer and a tractor truck is called a ''semi-trailer truck'' (also known simply as a "semi-trailer", "tractor trailer", or "semi" in the United Sta ...

– 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 (trailer), dolly. The coupling consists of a kingpin (automotive part), kingpin, a vertical steel pin protruding ...

on the

or the

semi-trailer truck A semi-trailer truck (also known by a wide variety of other terms – see below) is the combination of a tractor unit and one or more semi-trailers to carry freight. A semi-trailer attaches to the tractor with a type of hitch called ...

. Small semi-trailer such as

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

and boat trailer 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, also known as a land train or long combination vehicle (LCV) is a semi-trailer used to move road freight more efficiently than single-trailer semi-trailers. It consists of one semi-trailer or more connected together with or wit ...

– 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, also known as a land train or long combination vehicle (LCV) is a semi-trailer used to move road freight more efficiently than single-trailer semi-trailers. It consists of one semi-trailer or more connected together with or wit ...

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

semi-trailer A semi-trailer is a trailer (vehicle), trailer without a front axle. The combination of a semi-trailer and a tractor truck is called a ''semi-trailer truck'' (also known simply as a "semi-trailer", "tractor trailer", or "semi" in the United Sta ...

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 internal combustion engine, engine and transmission (mechanics), transmission layout used in motor vehicles, in which the engine drives the front wheels only. Most modern front-wheel-drive vehicles feature ...

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 (vehicle), trailer or machinery such as that used in agriculture, mining or constructio ...

. 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'' dolly, equipped with a ''gooseneck'' type drawbar that attaches to the fifth wheel coupling on the rear of a prime mover 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 country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

, 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 loaders 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, tr ...

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 means baggage trolleys used by individual passengers.

Aircraft ground carriage

An aircraft ground carriage / ground power assisted takeoff and landing concept is a landing gear system connected to the ground, on which aircraft can take off and land without their aircraft-installed landing gear.

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 United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

, USA
Images of trailer dollies
Trucks Trailers Types of take-off and landing