The X40 is a double-deck electric multiple unit from the Alstom Coradia Duplex family. Designed to replace slow loco-hauled commuter trains, they have 800 kW per car and can reach a top speed of 200 km/h. The first orders came for the Svealandsbanen in the Mälaren Valley west of Stockholm and more were ordered for the Gävle-Stockholm-Linköping line.
In total, SJ ordered 16 two-car sets and 27 three-car sets. Since one set was damaged beyond repair in an accident while still being in Germany, only 42 arrived in Sweden. Although designed for commuter traffic, they are also being used over longer distances, what led to the removal of some seat rows to create space for luggage. Since 2023, the trains are now being refurbished in Finland.