The Marunouchi Line (丸ノ内線) is a railway line of Tokyo Metro (東京地下鉄). It has a main line from Ikebukuro Station in Toshima ward to Ogikubo Station in Suginami ward, and a branch from Nakano-sakaue Station in Nakano ward to Honancho Station in Suginami ward.
History
The name Marunouchi comes from an area near Tokyo Station. The line began as Route 4 in a city rail plan. On 30 March 1925 the Home Ministry listed Route 4 as Shinjuku to Otsuka, 20.0 km long. Tokyo City received the licence on 16 May 1925. Tokyo City planned to build Line 3 and Line 5 first, but the Home Ministry and the Ministry of Finance opposed this because the city had large public debt, and permission was refused. On 1 October 1932 Tokyo City transferred part of its Route 3 and Route 4 licences to Tokyo Rapid Railway (東京高速鉄道). Tokyo Rapid Railway opened Route 3 as the Ginza Line. On 12 February 1937 it received a licence for Yotsuya-mitsuke to Akasaka-mitsuke. Akasaka-mitsuke Station, opened in 1938, had two levels from the start. On 1 September 1941 all these licences were transferred for payment to the Teito Rapid Transit Authority (帝都高速度交通営団, called Eidan), which had been founded on 4 July 1941. The Pacific War began on 8 December 1941. Eidan treated Route 4 as urgent work. The Yotsuya-mitsuke to Akasaka-mitsuke section had a groundbreaking ceremony on 5 June 1942. Work stopped on 16 June 1944, because the war had worsened and there was too little money, materials and labour.
After the war, a new plan set Route 4 at 22.1 km. On 23 May 1949 Eidan received the licence for Shinjuku to Ikebukuro, 16.86 km long. On 12 December 1949 construction of Ikebukuro to Kanda, 7.7 km, was decided. Ground was broken at the Ikebukuro East Exit on 30 March 1951. In November 1953 the route was changed to pass through Otemachi instead of near Kanda Station, because building there was too hard for the budget, the schedule and the technology. The first section, from Ikebukuro (a temporary station) to Ochanomizu, 6.4 km long, opened on 20 January 1954. It was Japan's fourth subway, after the Ginza Line and the Osaka City Subway's Midosuji and Yotsubashi lines, and the first one opened in Japan after the Second World War.
Extensions followed in stages. Ochanomizu to Awajicho opened on 20 March 1956, with 400 series cars brought in for the opening. Awajicho to Tokyo opened on 20 July 1956. Tokyo to Nishi-Ginza opened on 15 December 1957, with 500 series cars. Nishi-Ginza to Kasumigaseki opened on 15 October 1958. On 15 March 1959 Kasumigaseki to Shinjuku opened, with Shinjuku as a temporary station, and the Ikebukuro to Shinjuku line was complete. In November 1960 Ikebukuro and Shinjuku changed from temporary stations to permanent ones.
In 1957 the Ministry of Construction set out Route 4 as a 27.4 km main line to Ogikubo, with a 2.7 km branch from Nakano-sakaue to Honancho. The notice was dated 17 June 1957. The purpose was to reduce crowding on the Chuo Line of the national railways (国鉄中央線) by running along the Ome Kaido road (青梅街道) to Ogikubo, and to fill a gap in rail service around the depot area. Eidan received the licence on 1 March 1958, and construction began on 14 March 1959. On 21 October 1960 the section west of Shinjuku was named the Ogikubo Line (荻窪線). On 8 February 1961 Shinjuku to Shin-Nakano and Nakano-sakaue to Nakano-Fujimicho opened. From then, every second Ikebukuro to Shinjuku train ran through to the Ogikubo Line. Shin-Nakano to Minami-Asagaya opened on 1 November 1961. Minami-Asagaya to Ogikubo opened on 23 January 1962, which completed Shinjuku to Ogikubo. Nakano-Fujimicho to Honancho opened on 23 March 1962, which completed the whole Ogikubo Line. Fares were separate at first. A trip between the Ginza or Marunouchi lines and the Ogikubo Line cost 40 yen, not one flat fare. On 1 November 1961 distance-based fares were introduced on all Eidan lines.
In 1962 Eidan received a licence for Ikebukuro to Mukōhara (向原). Construction did not start, because the Ministry of Finance did not approve the budget. On 29 August 1964, when the Hibiya Line opened between Kasumigaseki and Higashi-Ginza, Nishi-Ginza Station was renamed Ginza Station and combined with the Ginza Line station. In 1968 the route was cut back to end at Ikebukuro, and the section beyond Ikebukuro was split off as Line 8, the Yurakucho Line (有楽町線). On 1 April 1972 the Ogikubo Line was renamed the Marunouchi Line, so the whole line had one name. In November 1981 the branch line's two-car sets were rebuilt into six three-car sets to increase carrying capacity. In the late 1990s a plan to extend the line from Ogikubo to Asaka through Nerima was raised in the Tokyo Metropolitan Assembly. It never became concrete and was dropped.
On 17 October 1988 the 02 series began regular service. Air-conditioned cars began running on 18 July 1990. On 28 February 1995 the 500 series ended service on the main line, so old cars ran only on the branch. On 28 May 1996 Nishi-Shinjuku Station opened between Nakano-sakaue and Shinjuku. On 18 July 1996 the last old cars on the branch were retired, so every car on the line was air-conditioned. On 27 February 1998 the line changed to the new CS-ATC signalling system across the whole line, and the main line's top speed rose from 65 km/h to 75 km/h. On 1 April 2004 Eidan was privatised and its business passed to Tokyo Metro (東京地下鉄). From 2006 to September 2007 platform screen doors were installed at the stations between Ikebukuro and Ogikubo.
On 27 December 2008 trains began automatic train operation (ATO) between Ikebukuro and Ogikubo. On 28 March 2009 the whole Ikebukuro to Ogikubo section went to one-person operation. In November 2016 the branch line's station codes changed from m to Mb, so that the branch stations could be told apart in automatic announcements from the nearby main-line stations. On 23 February 2019 the 2000 series entered service. On 5 July 2019 the Honancho platform was lengthened for six-car trains, and six-car trains began running from Ikebukuro to Honancho. On 6 June 2020 passengers could change between Ginza Station and Ginza-itchome Station on the Yurakucho Line. On 27 August 2022 the three-car trains on the branch ended, and all trains became six-car. In November 2022 trial runs of CBTC began between Yotsuya and Ogikubo. On 7 December 2024 the whole line began using CBTC, a wireless train control system.
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Written by an AI from the line's history on Japanese Wikipedia, nothing else, and checked by a program for dates and numbers that are not in those facts. It can still be wrong. Adapted from Japanese Wikipedia, CC BY-SA 4.0; this text is shared under the same licence.