Toei Mita Line

Subway line in Tokyo, Japan

The Toei Mita Line (都営地下鉄三田線) is a subway line of the Tokyo Metropolitan Bureau of Transportation (Toei) network in Tokyo, Japan. The line runs between Nishi Takashimadaira in Itabashi and Meguro in Shinagawa. Trains continue with direct service into the Meguro Line of Tokyu Corporation for The portion between and Meguro is shared with the Tokyo Metro Namboku Line. The line was named after the Toeimita district in Minato, Tokyo, under which it passes. On maps and signboards, the line is shown in blue. Stations carry the letter "I" followed by a two digit number.

Platforms on the Mita Line are equipped with chest height automatic platform gates that open in sync with the train doors. The line was the first in the Tokyo subway system to have low barriers. The Tokyo Metro Namboku Line has used full height platform screen doors since its opening. As of April 2022, the platform doors have been fully replaced for 8 car operations

The right of way and stations between Shirokane Takanawa and Meguro are shared with the Tokyo Metro Namboku Line a unique situation on the Tokyo subway where both operators share common infrastructure. Under an agreement of both parties, the fare for this section is calculated on the Toei system for passengers travelling to stations on the Mita Line past Shirokane Takanawa, using the Tokyo Metro system for those travelling on the Namboku Line past Shirokane Takanawa, and on the system "most beneficial to the passenger" (presently the Tokyo Metro schedule) for travel solely on the shared section. According to the Tokyo Metropolitan Bureau of Transportation, as of June 2009, the Mita Line is the ninth most crowded subway line in Tokyo, running at 164% capacity between Nishi Sugamo and Sugamo stations.

The Mita Line was first envisioned in 1957 as a northern branch of Line 5 (the present Tōzai Line), serving the section between Ōtemachi and Itabashi. Under a revised proposal in 1962, the line was made independent and its construction was undertaken by the Tokyo Metropolitan Government. The new line (Line 6) was planned to run from Gotanda Station on the southwestern side of the Yamanote Line through central Tokyo, with its northern extensions via Yamatochō (大和町) in Itabashi (near present ), diverting to and Shimura (志村) (present ). The southernmost portion, from to and Nishi Magome depot, was to be shared with Line 1 (Asakusa Line); therefore, Line 6 would be 1435 gauge. Due to political considerations, the design of the Mita Line changed several times during the early 1960s. There were plans for it to run to Toda, Saitama, to serve a boat racing venue for the 1964 Summer Olympics. The government of Saitama also proposed the construction of a new subway line which would allow through service on the Mita Line as far as Ōmiya Station. In 1964, these plans were changed to allow the Mita Line to connect with the Tōbu Tōjō Line via a branch to be built by Tobu between Yamatomachi (大和町) (now ), and Shimura, the northern end of Line 6. At the southern end, the junction with the Tokyu network would be via a connecting line, which would be constructed by Tokyu from Sengakuji to Kirigaya (桐ヶ谷) on the Tōkyū Ikegami Line; the route would continue to the then Den en toshi Line and finally west, down to As a result, the construction standards of Line 6 were based on those of Tobu and Tokyu (such as 1067 gauge track and 20 meter long cars today, the Mita Line is the only Toei line to use this gauge). A depot was planned at Shimura, independent of the Nishi Magome depot on Line 1. However, both Tokyu and Tobu decided the following year to operate their thorough services with the Teito Rapid Transit Authority (TRTA, now Tokyo Metro) lines instead. With no thorough service opportunities available the Tokyo Metropolitan Government began construction on the central portion of the line, leaving the plans for the Itabashi and Mita ends open for future development. This required an extension somewhere south of Seishōkō mae (清正公前) (present ), probably to the then Mekama Line of Tokyu (on the commencement of inter running to Mita and Namboku lines, the Mekama Line was divided into the Meguro Line and Tōkyū Tamagawa Line) which competed with TRTA Line 7, later called the Tokyo Metro Namboku Line. The first segment of the line opened on 27 December 1968, between and The line was extended a further south to on 30 June 1972, and further south to Mita on 27 November 1973. The northern extension (originally licensed to Tobu and later transferred to Toei Subway) was completed on 6 May 1976. For the next 24 years, the line operated between Mita and Nishi Takashimadaira; the authorized Mita and Sengakuji section had been left uncompleted. In 1985 the then Ministry of Transport finally settled the plan regarding the southern extension of the line and shelved all plans for further extension to the north due to the development of the Saikyō Line. On 26 September 2000, the final 4 km segment from Mita to Meguro opened, and through service to the Meguro Line of Tokyu began at the same time, at which point the line switched to driver only operation. By the end of 2020, all platform screen doors on the Mita Line were extended to accommodate 8 cars in preparation of the Sōtetsu Tōkyū Link Line through service from the Sotetsu Line. Mita Line through services to and from the Sotetsu Line began operation on 18 March 2023. Effective this date, the Mita Line provides through services as far south as Ebina on the Sotetsu Main Line and Shonandai on the Sotetsu Izumino Line, with a fraction of trips turning around at Shin Yokohama Station. Most local services still make it as far south as Hiyoshi on the Tokyu Toyoko Line with some peak hour trips terminating at Musashi Kosugi (also on the Toyoko Line).