Bo-Bo or Co-Co

Bo-Bo is the UIC indication of a wheel arrangement for railway vehicles with four axles in two individual bogies, all driven by their own traction motors. It is a common wheel arrangement for modern electric and diesel-electric locomotives, as well as power cars in electric multiple units.

Co-Co is a code for a locomotive wheel arrangement with two six-wheeled bogies with all axles powered, with a separate motor per axle. Co+Co is the code for a similar wheel arrangement but with an articulated connection between the bogies. The equivalent UIC classification for this arrangement is Co′Co′.