A Bo-Bo-Bo or Bo′Bo′Bo′ (

UIC classification The UIC classification of locomotive axle arrangements, sometimes known as the German classification''The Railway Data File''. Leicester: Silverdale, 2000. p. 52. . or German system,Kalla-Bishop P.M. & Greggio, Luciano, ''Steam Locomotives'', Cre ...

) is a locomotive with three independent two-axle

bogies 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 tran ...

with all

axle An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, beari ...

s powered by separate

traction motor A traction motor is an electric motor used for propulsion of a vehicle, such as locomotives, electric or hydrogen vehicles, elevators or electric multiple unit. Traction motors are used in electrically powered rail vehicles ( electric multipl ...

s. In the AAR system, this is simplified to B-B-B. The Bo-Bo-Bo configuration is often used to lower axle weight while keeping lateral forces low compared to a locomotive with two three-axle bogies, thus allowing the locomotive to use lightly laid track, in particular narrow-gauge railways.

Bo-Bo-Bo locomotives

The arrangement is extensively used on Italian and Japanese railways. Other examples include

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 List of islands of New Zealand, smaller islands. It is the ...

's DJ, EW and EF classes; the Eurotunnel Class 9 locomotives, which were themselves derived from the New Zealand EF class; the Swiss SBB Re 6/6 (Re 620); the Russia Railways VL65, EP1 (EP1M), EP10 and EP20; and the

South Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korea, Korean Peninsula and sharing a Korean Demilitarized Zone, land border with North Korea. Its western border is formed ...

n Korail Class 8000. China imported 6K

electric locomotive An electric locomotive is a locomotive powered by electricity from overhead lines, a third rail or on-board energy storage such as a battery or a supercapacitor. Locomotives with on-board fuelled prime movers, such as diesel engines or ga ...

from Japan between 1986 and 1987. The Bo-Bo-Bo design was applied to SS7 series except SS7E. The

State Rail Authority The State Rail Authority, a former statutory authority of the Government of New South Wales, operated and maintained railways in the Australian state of New South Wales from July 1980 until December 2003. History The ''Transport Authorities ...

of NSW built the last of its 86 Class electric locomotives (8650) in the Bo-Bo-Bo arrangement (called locally a Tri-Bo), but this did not prove successful and it spent long periods out of traffic undergoing repair. The first Italian six-axle electric locomotives, such as the E.626, used a Bo′BoBo′ layout, where the two centre axles were mounted on a rigid frame and only the outer pairs on bogies. This wheel arrangement requires either an articulated frame (becoming a Bo+Bo+Bo arrangement) or else significant side play on the center bogie. The Italian locomotives and New Zealand EW class are articulated, whereas the Eurotunnel and New Zealand EF and DJ class locomotives' central bogies have a lot of sideplay.

B′B′B′ locomotives

A similar arrangement, but without separate traction motors for each axle, would be a B′B′B′ arrangement as UIC, indistinguishably B-B-B in AAR. This arrangement has been used for electric locos with three monomotor bogies, such as the Italian FS Class E.632 of 1982.

Bo′Bo′Bo′+Bo′Bo′Bo′ locomotives

These are a pair of Bo′Bo′Bo′ locomotives semi-permanently coupled as a single unit. They are each constructed with a single cab, giving a cab at each end. This layout includes Russian freight electric locomotives VL15, VL85, VL86f and the experimental gas turbine electric locomotive GT1h-001, which was converted from an electric locomotive VL15.

Bo-Bo-Bo locomotives

B′B′B′ locomotives

Bo′Bo′Bo′+Bo′Bo′Bo′ locomotives

See also