Nippori–Toneri Liner

The corridor it follows had long been a transit gap. Western Adachi and the area along Ōku-bashi-dōri (Tokyo Metropolitan Road No. 58) lay far from existing railways, and demand was carried by the heavily crowded Toei Bus route 48 (里48) between Nippori and the Toneri area. That road also handled heavy lorry traffic to facilities such as the Adachi truck terminal (opened 1977) and the Kita-Adachi market (1979), so chronic congestion repeatedly made the buses unable to keep to schedule, and residents wanted a rail- or tramway-based service that could move large numbers reliably and on time.

Momentum for a railway began in 1974, when Koganei Shunsuke, an executive of the Adachi branch of the Liberal Democratic Party, began campaigning to attract a line. The route was formally positioned in July 1985 by Transport Policy Council Report No. 7, which envisaged replacing the Toei Bus 48 corridor with a medium-capacity system. It was initially planned as part of Subway Line 7 (today's Namboku Line), but for reasons of finance and projected profitability the plan was changed to a more cost-efficient AGT system running above Ōku-bashi-dōri. Reflecting those same budget constraints, the tramway-business licence did not come until 1995 and construction authorisation until 1997; ground was broken on 1 December 1997. Because settling the project's operator and acquiring land on the Arakawa side took time, the opening — first planned for fiscal 1999 — slipped to fiscal 2002 and then to 30 March 2008, two postponements in all.

Responsibility for running the line was originally to fall to the Tokyo Metropolitan Subway Construction Company, which had built part of the Toei Ōedo Line. On grounds of profitability and of strengthening the Toei transport network, it was instead decided that the Tokyo Metropolitan Bureau of Transportation would take over the tramway-business licence from that company and operate the line itself. The infrastructure was split between two metropolitan bodies: the piers and girders were built by the Bureau of Construction as a city-planning road project, while the track, stations and other railway facilities were built by the Tokyo Metropolitan Subway Construction Company as a city-planning urban high-speed railway project.

The line's name was chosen by public competition. The Bureau of Transportation and the Subway Construction Company invited submissions from 15 to 31 August 2006; after deliberation by a selection committee the route name "Nippori-Toneri Liner" was settled, and it was announced together with the station names on 13 November 2006. The line opened on 30 March 2008 between Nippori and Minumadai-shinsuikōen, 9.7 km with 13 stations. It was the second publicly operated AGT line in Japan, after the Osaka municipal Nankō Port Town Line (New Tram) of 1981; once that line passed to the Osaka Metro company in 2018, the Nippori–Toneri Liner became the only publicly operated AGT line in the country.

Demand outran the planners' cautious expectations. At the 1995 licensing the line had been forecast to carry about 101,000 passengers a day, a figure revised down to 59,000 in fiscal 2003, on which basis the choice of AGT and the train formations were fixed. In its first year, fiscal 2008, the line carried an average of 48,943 passengers a day; by fiscal 2010 it had already reached the fiscal-2003 forecast, and ridership kept climbing — to about 90,737 a day in fiscal 2019 and 95,240 in fiscal 2024. The flip side was severe rush-hour crowding, worsening year by year along the busiest segment from Akado-shōgakkōmae toward Nishi-Nippori. Toei responded with repeated timetable revisions and shorter headways — the morning interval was tightened to as little as around three minutes — and by heavier rolling stock: the original 300 series of 2008 was joined by the all-longitudinal-seat 330 series from 2015 and the 320 series from 2017, raising capacity. Even so, the line became one of Japan's most crowded.

Two events stand out in operations. After the Tōhoku earthquake of 11 March 2011 the whole line was suspended; following equipment checks it resumed at 14:00 on 13 March, and ran on reduced power-saving timetables through to 9 September 2011. Then, late on 7 October 2021, a magnitude-5.9 earthquake partly derailed three cars of a train at about 10:41 pm, injuring three passengers with no fatalities; repairs were expected to take several days. The crowding problem, meanwhile, became the line's defining feature: its congestion rate peaked at 189% in fiscal 2018 and 2019, and from fiscal 2020 through fiscal 2024 the Nippori–Toneri Liner recorded the highest congestion rate of any line in Japan for five straight years, the fiscal-2024 peak-hour figure being 177% on the Akado-shōgakkōmae → Nishi-Nippori section.

• 1974Koganei Shunsuke, an executive of the Adachi branch of the Liberal Democratic Party, begins campaigning to attract a railway to the corridor.
• 1985July: Transport Policy Council Report No. 7 positions the line, aiming to replace the Toei Bus route 48 corridor with a medium-capacity system; originally planned as part of Subway Line 7 (now the Namboku Line).
• 1995The tramway-business licence is obtained.
• 19971 December: construction authorisation is granted and ground is broken; the plan had by now been changed from a subway to a more cost-efficient AGT on Ōku-bashi-dōri.
• 200615–31 August: a public competition is held to name the line.
• 200613 November: the route name 'Nippori-Toneri Liner' and the station names are announced.
• 200830 March: the line opens between Nippori and Minumadai-shinsuikōen — 9.7 km, 13 stations; Japan's second publicly operated AGT after Osaka's New Tram (1981). First-year (FY2008) ridership averages 48,943 a day.
• 200812 July: the first timetable revision adds trains and revises curve speeds near Nippori to prevent accidents on the sharp curve there.
• 201111 March: the line is suspended by the Tōhoku earthquake; service resumes at 14:00 on 13 March, then runs on power-saving timetables until 9 September 2011.
• 201510 October: the aluminium-bodied 330 series, with all-longitudinal seating, enters service to raise capacity.
• 201710 May: the 320 series (set 21) enters service.
• 2018The congestion rate reaches 189% on the AM-peak Akado-shōgakkōmae → Nishi-Nippori section (FY2018), among the highest of any Tokyo line.
• 20217 October: a magnitude-5.9 earthquake partly derails three cars of a train at about 10:41 pm; three passengers are injured, with no fatalities.
• 2024FY2024: the Nippori–Toneri Liner records Japan's highest congestion rate for the fifth straight year (since FY2020), at a peak-hour 177% on Akado-shōgakkōmae → Nishi-Nippori; daily ridership averages 95,240.