The underground railway service in Helsinki was opened in 1982 and consisted of a single line, which ran from the city centre to the eastern suburbs, where it then divided into two separate branches. Plans already existed in the 1990s to extend the underground in a westerly direction to the neighbouring town of Espoo. For political and economic reasons, however, the implementation of these plans drew itself out because the first stretch was to pass beneath the Baltic and involved a correspondingly high investment. 

In the end, agreement was reached to build the new stations with a platform length of only 90 metres instead of 135 metres, as had been the case previously, and to have shorter trains running at a greater frequency. At the end of 2017, the first eight stations were taken into operation. A further five are under construction.