Bo-Bo-Bo

A Bo-Bo-Bo in UIC classification is a locomotive with three independent two-axle bogies with all axles powered. In the AAR system, this is simplified to B-B-B.

Bo-Bo-Bo locomotives are more common in narrow-gauge railways where the additional traction is highly beneficial, but are used in standard gauge railways, such as the Eurotunnel Class 9 locomotives. The configuration is often used to lower axle weight on a locomotive's bogies, thus allowing the locomotive to use lightly-laid track.

Bo-Bo-Bo electric locomotives are extensively used on Italian and Japanese railways. New Zealand's DJ, EW and EF classes locomotives use this configuration, as do Swiss Re 6/6 (Re 620).

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.

China imported 6K electric locomotive from Japan between 1986 and 1987. The Bo-Bo-Bo design was applied to SS7 series except SS7E.

This wheel arrangement requires either an articulated frame or significant side play on the center bogie.

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