The three-part Dm3 have been in use for decades on the Luleå–Narvik railway line, which connects the Swedish ore mines near Kiruna and Gällivare with the ports in Luleå, Sweden and Narvik, Norway. To replace these, the IORE was ordered from ADtranz in the 1990s, the name of which is derived from “Iron Ore”. Although these locomotives were later assigned to the TRAXX family by Bombardier, they were actually independent developments that had been developed by the Swiss branch in Oerlikon.
These are double locomotives that consist of two technically independent, six-axle locomotives. Since the ore trains on this route operate at 60 km/h when loaded and at 70 km/h when empty, the maximum speed was limited to 80 km/h. This means that a double locomotive achieves a starting tractive effort of 1,400 kN (315.000 pounds) and can therefore pull trains weighing 8,600 tonnes and containing 6,880 tonnes of iron ore. The vehicles are designed for the harsh climate north of the Arctic Circle and also have appropriate equipment in the cabs.
The axle load was initially 25 tonnes, but was increased to 30 tonnes with ballast after the line was upgraded and new, larger ore hoppers were introduced. Due to increased production in the mines, the Dm3 could not be completely replaced with the nine double units initially ordered. Only after two more orders, which brought the number of pairs to 17, was the last Dm3 could be retired in 2013.
