Around our major cities, railway traffic increasingly reaches the maximum capacity of the tracks. Additionally, an old railway route rarely meets the needs of a modern city. A common solution to both problems is becoming a completely new railway through the city, this time underground.

Both in Malmö and Gothenburg, it was decided early on not to run the railway through the city. Instead, 'terminal stations' were established. Trains take the same route to and from the central station and make a turn outside the city centre before continuing further. The railway thus becomes inaccessible to large parts of the central city. In Stockholm, however, the railway was built straight through the city with the Sammanbindningsbanan (Connecting Line) in the 1870s.

In all three cases, the maximum capacity was eventually reached, and in all cities, there is no possibility of expanding existing tracks with more tracks. The solution is instead to build completely new tracks, but this time underground. In all three cases, the railway is drawn under the cities in tunnels approximately six kilometres long.

The City Tunnel in Malmö was inaugurated in 2010, the Stockholm City Line was completed in 2017, and the West Link in Gothenburg is expected to be completed in 2026. In addition to increasing the total capacity, the tunnels provide a better-placed railway in the cities. In all three cases, several underground stations are being built along the new route in central locations, resulting in greater accessibility.