page_title: Helsinki Metro
section_title: 1969–82: Construction
hierarchical_section_title: Helsinki Metro / History / 1969–82: Construction
caption_attribution_description: English: Kontula metro station, Helsinki, Finland Suomi: Kontulan metroasema, Helsinki
context_page_description: The Helsinki Metro is a rapid transit system serving Greater Helsinki, Finland. It is the world's northernmost metro system. The Helsinki Metro was opened to the general public on 2 August 1982 after 27 years of planning. It is operated by Helsinki City Transport for HSL and carries 63 million passengers per year.
  The metro system consists of 2 lines, which serve a total of 25 stations. It has a total length of 35 kilometres. The metro serves as the predominant rail link between the suburbs of East Helsinki and the western suburbs in the city of Espoo and downtown Helsinki.
  The line passes under the Helsinki Central Station allowing passengers to transfer to and from the Helsinki commuter rail network, including trains on the Ring Rail Line to Helsinki Airport.
context_section_description: 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. The first prototype train, units M1 and M2, arrived from the Valmet factory in Tampere on 10 November 1971, with further four units (M3–M6) arriving the following year. Car M1 burned in the metro depot in 1973.
  Excavating the metro tunnels under central Helsinki had begun in June 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. To build a tunnel through the bruise an unusual solution was developed: the bruise was turned into a giant freezer, with pipes filled with Freon 22 pushed through the clay. The frozen clay was then carefully blasted away, with cast iron tubes installed to create a durable tunnel. Construction of the first stations, Kulosaari and Hakaniemi begun in 1974. The Kulosaari station was the first to be completed, in 1976, but construction of the other stations took longer. As the case with many underground structures in Helsinki, the underground metro stations were designed to also serve as bomb shelters.
  In summer 1976 Teuvo Aura, the city director of Helsinki, signed an agreement with Valmet and Strömberg to purchase the trains required for the metro from them. In doing so Aura bypassed the city council completely, reportedly because he feared the council would decide to buy the rolling stock from manufacturers in the Soviet Union instead. By this time the direct current–based technology of the M1 series trains had become outdated. In 1977 prototypes for the M100 train series (referred to as "nokkajuna", English: "beak train", to differentiate from the M1 prototypes) were delivered. In these units the direct current from the power rail was converted to alternating current powering induction motors. The M100 trains were the first metro trains in the world to be equipped with such technology.
  Aura's bypassing the city council in acquiring the rolling stock was not the only questionable part of the construction process of the Metro. On 3 June 1982, two days after the Metro had been opened for provisional traffic, Unto Valtanen came under investigation for taking bribes. Subsequently, several members of the metro committee and Helsinki municipal executive committee in addition to Valtanen were charged with taking bribes. In the end it was found that charges against all the accused except Valtanen had expired. Valtanen was convicted for having taken bribes from Siemens.
caption: One of the M100 series prototypes, number 106 (right) at Kontula station.
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