The EMD SD90MAC is a model of C-C diesel-electric locomotive produced by General Motors Electro-Motive Division. It is, with the SD80MAC, one of the largest single-engined locomotives produced by EMD, surpassed only by the dual-engined DDA40X. The SD9043MAC is the variant, using a 16-cylinder 710G engine instead of the H-engine, which was originally intended as a temporary alternative while EMD tried to solve the H-engine's issues. However, the accompanying upgrade program was never utilized by its customers. The SD90MAC's features include radial steering trucks with AC traction motors and an isolated safety cab which is mounted on shock absorbers to lessen vibrations in the cab. The SD90MAC, like the SD80MAC, SD70ACe, and SD70M-2, has a wide radiator section, nearly the entire width of the locomotive, which along with their size makes them easy to spot. As of 2019, some SD90MACs are still in service on the Union Pacific. Norfolk Southern had rostered 110 SD90MAC locomotives purchased or traded from Union Pacific or the CIT Group respectively, that have now all been rebuilt as EMD SD70ACU locomotives. Canadian Pacific has also opted to convert their small fleet of long-stored SD90MACs into SD70ACUs as well. History The SD90MAC was introduced in 1995, along with the SD80MAC locomotives. The SD90MAC was designed to utilize the new 16-cylinder H-engine, while the SD80MAC was designed to use the 20-cylinder version of the existing 710G engine. However, technical problems with the engine resulted in the first locomotives being shipped with 16-cylinder 710G engines, making them similar to the SD70MAC's. These locomotives were informally designated SD9043MAC by railroads that purchased them with the option to re-engine them with engines when they became available. This upgrade program, however, was never taken advantage of by SD90MAC buyers due to reliability issues with the newer engine. Over 400 SD90MAC locomotives fitted with the 710 engine were built. In 1996, Electro-Motive Diesel entered full production on their , 16-cylinder H-engine, and all SD90MACs made from then on used that for its prime mover. Locomotives fitted with this engine are sometimes referred to as SD90MAC-H locomotives. Later versions of the SD90MAC-H feature a Phase II cab, with a new nose which offers higher visibility from the cab than the old nose. The SD90MAC-H did not prove popular with railroads and less than 70 were built, including Electro-Motive Diesel demonstrator units. Since the SD90MAC-H had such a large prime mover, it didn't offer