The M7 was an electric multiple unit designed in the nineties to replace the M1 and ACMU on the Long Island Railroad and Metro-North. Each unit is being formed from two cars as a married pair. Each car in the pair has one cab and each axle is being powered by a 265 hp three-phase AC traction motor. Between 1999 and 2006, 418 pairs were built for the LIRR and 168 for Metro-North. The vehicles for Metro-North have some changes and are being designated M7A. In fall 2006 many had to be taken out of service due to severe slipping problems when braking on tracks covered with leaves. Around the same time the armrests in all cars were replaced since the old ones were notorious for damaging trousers when standing up from the seat.