Track and depot
In Helsinki, the metro goes through a tunnel from Ruoholahti to Sörnäinen and rises above the ground after Sörnäinen. In the western section, from Ruoholahti to Matinkylä, the metro will stay underground.
The metro has two tracks, one to the east and one to the west. In Helsinki, the track is 21.1 kilometres long. The west metro track from Ruoholahti to Matinkylä is 13.9 kilometres long. The metro track is like a wide-tracked railway track: the width of a track is 1,522 mm. The metro track is completely separated from its environment, ensuring reliable operations.
The maximum allowed speed is usually 80 kilometres per hour, and in the city centre tunnel 70 kilometres per hour. The metro trains are supplied with the necessary electricity from the bus bar running along the track. It is covered with a yellow protective casing. The bus bar has a voltage of 750 V DC.
Between Ruoholahti and Sörnäinen, the track goes through the inner city in a tunnel dug into the bedrock. Measured from the ground surface, the tunnel is at its deepest at Torkkelinmäki, Kallio, where it is 42 metres underground. Measured from the sea surface, the deepest place is under Pitkänsilta Bridge, where the track’s depth is 28 metres.
Between the stations of Rautatientori and University of Helsinki, the metro track goes through the so-called ‘Kluuvin ruhje’, a depression in the bedrock. There is no solid bedrock in this depression, and the soil is clayey and broken. Building the metro tunnel into this depression was one of the biggest challenges of the metro construction project; the soil had to be first frozen so that it could be excavated. These days, the metro trains pass the location through a cast-iron tube.
In addition to the city centre, the metro track goes through a tunnel on both sides of Puotila. Also in Mellunmäki, the turnaround track has been excavated into the bedrock, reaching all the way to Vantaa. The test track at the metro depot also has its own bedrock tunnel.
Many measures have been put in place to ensure the safety of these tunnels. For example, the metro tunnels have been equipped with fire alarm and smoke extraction systems, and there are emergency exits between the stations.
The track above ground
Coming from the city centre, the track rises above the ground after Sörnäinen metro station. For around half a kilometre, the track goes along the Junatie Bridge, on which Kalasatama metro station is also located. The track goes over Vanhankaupunginlahti Bay on the Kulosaari metro bridge and veers towards Itäkeskus along Itäväylä. Underneath Itis shopping centre, the track divides into two branches, older of which goes to Mellunmäki and the newer to Vuosaari.
Metro trains are stored, maintained and repaired at the metro depot in Roihupelto. HKL Metro Unit’s administration, warehouse, security equipment maintenance and track workshop also operate from the depot. The metro depot also has a test track on which the metro train fleet can be test driven at full speed.