The is a rapid transit line in Tokyo and Chiba Prefecture, Japan, owned and operated by Tokyo Metro. The line runs between Nakano in Nakano-ku, Tokyo and Nishi-Funabashi in Funabashi, Chiba Prefecture.
The TÃ Âzai Line was referred to as Line 5 during the planning stages; the seldom-used official name is .
In 2024, the line carried a daily average of nearly 1.5 million passengers, making it the busiest line on the Tokyo subway network. On maps, diagrams and signboards, the TÃ Âzai Line is shown using the color "sky blue" and its stations are given numbers using the letter "T".
The line runs through central Tokyo from east to west via Takadanobaba, Waseda, Ã Âtemachi, Nihombashi, Kiba and Urayasu. It was opened as a bypass route for the Chuo Rapid Line and the Sobu Line, which were heavily congested at the time. It is the only Tokyo Metro line to extend into Chiba Prefecture (although the Shinjuku Line operated by Toei also extends into Chiba Prefecture.) It also runs above-ground for from to , nearly half of the line and longer than any other railway line in the Tokyo subway network.
The Tà Âzai Line features through services at both ends of the line. Trains run onto the JR East Chà «à Â-Sà Âbu Line for at the western (Nakano) end, and onto either the Chà «à Â-Sà Âbu Line for or the Tà Âyà  Rapid Railway Line for at the eastern (Nishi-Funabashi) end.
According to the Tokyo Metropolitan Bureau of Transportation in 2018, the Tokyo Metro TÃ Âzai Line continues to be most crowded subway line in Tokyo, and the most crowded train line in all of Japan, with its peak running at 199% capacity between and stations. Women-only cars were introduced on the line for use during morning rush hour on November 20, 2006.
During the COVID-19 pandemic, peak ridership dropped from a rate of 199% in 2019 to 123% in 2020.
The original plan for what is now the Tà Âzai Line was included in a report by the Tokyo City and Area Transportation Research Committee (æ±京å¸Âå å¤Â交éÂÂ調æ»å§Âå¡ä¼Â), which was established within the Ministry of Home Affairs in 1917. The proposal outlined a route connecting âÂÂIkebukuro â Takadanobaba â Iidabashi â Otemachi â SusakiâÂÂ.
In 1920, a construction patent for this route was granted to the Tokyo Railway (æ±京éÂÂéÂÂ). However, following the Great Kantà  Earthquake of 1923, the patent was revoked along with those for other planned lines because construction had not yet commenced.
The route license for the Tà Âzai Line originates from the six municipal subway lines planned by Tokyo City, the predecessor of todayâÂÂs Tokyo special wards, prior to World War II. The license was granted on May 16, 1925, under Ministry of Home Affairs Notification No. 56 of 1925 ().
The present Tà Âzai Line corresponds to the former Line 5, which was authorized as a 14.2-kilometer route running from âÂÂIkebukuro â Waseda â Iidamachi â Hitotsubashi â Tokyo â Eitaibashi â SusakiâÂÂ. As part of the initial phase of the Tokyo Municipal Subway project, Tokyo City planned to begin construction on Line 3 between Shibuya and Sugamo and on Line 5 between Ikebukuro and Susaki. However, due to the cityâÂÂs substantial public debt and concerns over deteriorating finances, the Ministry of Home Affairs and the Ministry of Finance opposed the project, and construction approval was not granted.
Following this setback, no further construction plans were pursued, and the Teito Rapid Transit Authority, commonly known as the Eidan Subway, was subsequently established. In 1941, all subway route licenses held by the Tokyo municipal government were transferred to the Teito Rapid Transit Authority in exchange for compensation.
By contrast, the section corresponding to the present-day Tà Âyà Âchà  to Nishi-Funabashi segment was originally licensed to the (æ±京æÂÂèÂÂé»æ°ÂéÂÂéÂÂ) prior to World War II. The application was approved in 1927, with the eastern terminus Tà Âyà Âchà  designated as Higashi-hirai. However, this license ultimately expired in 1940 after construction failed to proceed.
The Tà Âzai Line was planned by a review committee of the then Ministry of Transportation in 1962 and numbered Line 5. Its name literally means "East-West Line", and it was primarily planned to relieve traffic on the busy Sà Âbu Main Line as well as provide a straight crosstown connection through north-central Tokyo. Although this corridor is also served by the Tokyo Metropolitan Bureau of Transportation (Toei) Shinjuku Line and JR Keiyà  Line, the Tà Âzai Line continues to operate beyond capacity due to its accessibility to other lines, as well as to growing condominium developments in eastern Tokyo.
The to section opened in 1964, and the remainder opened in stages until its completion in 1969. Through service with the then Japanese National Railways (today part of the JR Group) â a first for a Tokyo subway line â began in 1969 connecting the Chà «à  and Sà Âbu lines. This is a rare situation in Tokyo, as the only other subway line with through services onto JR lines is the Chiyoda Line.
Due to a surge in ridership on the TÃ Âzai Line, the Teito Rapid Transit Authority (TRTA) introduced 12 new-build 5000 series cars and transferred 50 from the Chiyoda Line in 1981 in an effort to increase capacity on the line. Rapid residential development in the Urayasu and Kasai areas further increased demand. In response, TRTA introduced rapid trains that ran non-stop between and stations, and stopped at every station west of , in November 1986.
The Tà Âyà  Rapid Railway Line, effectively an eastward extension of the line, opened in 1996. It nevertheless remains a private entity to which the Tà Âzai lines offers through services.
The TÃ Âzai Line was the first Tokyo Metro line on which express services run: two types of rapid trains skip some stations east of Toyocho. The Tokyo Metro Fukutoshin Line began services on June 14, 2008, and also features express services.
Through services to via the JR East Chà «à  Line and via the Tà Âyà  Rapid Railway run all day. Outside of rush hours, only local trains run through to the Chà «à  Line and only rapid trains run through to the Tà Âyà  Rapid Railway. During the morning and evening peak periods, through services run to via the JR East Sà Âbu Line.
TÃ Âzai Line trains are 10-car formations of -long cars, with four doors per side and longitudinal seating. The maximum operating speed is . Newer trains feature wide doors to allow for faster boarding times.
a. Crowding levels defined by the Ministry of Land, Infrastructure, Transport and Tourism: