[citation needed] In 1964 the city commissioned experts from Hamburg, Stockholm and Copenhagen to evaluate the metro proposal.

[13] Although no official decision to build a system along the lines proposed by Castrén was ever made, several provisions for a light rail metro system were made during the 1950s–1960s, including separate lanes on the Kulosaari and Naurissaari bridges,[11] and space for a metro station in the 1964 extension of Munkkivuori shopping center.

Prior to his departure Castrén indicated he planned to return to Helsinki in six months and continue his work as leader of the metro committee.

[citation needed] Construction of a 2.8-kilometre (1.7 mi) testing track from the depot in Roihupelto to Herttoniemi was begun in 1969 and finished in 1971.

Most of the tunneling work had been completed by 1976, excluding the Kluuvi bruise (Finnish: Kluuvin ruhje), a wedge of clay and pieces of rock in the bedrock, discovered during the excavation process.

The frozen clay was then carefully blasted away, with cast iron tubes installed to create a durable tunnel.

[21] In summer 1976, Teuvo Aura, the mayor of Helsinki, signed an agreement with Valmet and Strömberg to purchase the trains required for the metro from them.

[23] Aura's bypassing the city council in acquiring the rolling stock was not the only questionable part of the construction process of the Metro.

Trains ran with passengers during the morning and afternoon rush hours between Itäkeskus and Hakaniemi (the Sörnäinen station was not yet opened at this time).

[16][24] President of the Republic of Finland Mauno Koivisto officially opened the Metro for traffic on 2 August 1982 – 27 years after the initial motion to the city assembly had been made.

Within six months of the Metro's official opening, a petition signed by 11,000 people demanded the restoration of direct bus links.

On 31 August 1998, after four years of construction, the final section of the original plan was completed, with the opening of a three-station fork from Itäkeskus to Vuosaari.

[28] On 25 September 2006, the city council of Espoo approved, after decades of debate, planning, and controversy, the construction of a western extension of the Metro.

This first stage of the extension was 14 km (8.7 mi) long, with eight new stations, two in Helsinki and six in Espoo[37][38] and was built entirely in a tunnel excavated in bedrock.

To increase capacity, the automatic train protection system theoretically permits headway as short as 90 seconds, if required in the future.

[39] The decision to fund the construction of the second stage, from Matinkylä to Kivenlahti, was taken by the Espoo city council and the state of Finland in 2014.

The stations are located along a Y shape, where the main part runs from the Matinkylä through the center of the city towards the eastern suburbs.

[41] Some stations are located above ground level, making the metro system more friendly to passengers with mobility problems.

The HSL travel card (matkakortti) is the most commonly used ticket, which can be paid either per journey or for a period of two weeks to one year.

[43] A single ticket can be used to change to any other form of transport inside the HSL area with the validity time based on the number of zones purchased.

The newer M200 series was built by Bombardier and has been in service since 2000; each set is composed of two cars connected by an open gangway.

Unlike the first two series, the M300 trains operate as 4-car sets with open gangways and were designed to run without drivers, though since the cancellation of the automation project, they retain their temporary cabs.

The depot is connected to the metro line from both directions, with a third, central, platform at Itäkeskus used for empty services and during times of disruption.

Behind the Roihupelto depot is the metro test track, allowing testing at speeds of up to 100 kilometres per hour (62 mph); the far end of this test-track was until 2012 connected via the non-electrified 5 km (3.1 mi) long Herttoniemi harbour railway [fi] and then to the VR main line at Oulunkylä railway station.

[44] The new underground Sammalvuori metro depot [fi] located between Kivenlahti and Espoonlahti stations, opened along with the second stage of Länsimetro on 3 December 2022.

[47] Proposals also exist for the line to be extended even further east into central Sipoo, possibly as far as to Sibbesborg, to an envisioned new city centre there.

[48] A second Metro line from Laajasalo via Kamppi to Pasila north of the city centre, and possibly onwards to Helsinki-Vantaa Airport, is also in the planning stages.

On 17 May 2006 the Helsinki city council decided that the current, manually driven metro trains would be replaced by automatic ones, operated without drivers.

[50] In addition to the metro stations already in operation, forward-looking design has led to a number of extra facilities being constructed in case they are needed in the future.

According to the Helsinki Regional Transport Authority (HSL) yearly report for 2019, the metro system had a total of 92.6 million passengers.