Four variations of rolling stock operate on the MTR on 1.5kV DC overhead electrification. All trains are electric multiple units (EMUs), with ATC and ATP, operating on 1432 mm rail gauge. Except for the rolling stock of the Airport Express, all trains are designed with features to cope with high density passenger traffic on stopping services. Examples are the latitudinal seating arrangement, additional ventilation fans and 5 doors on each side per car.