Imazatosuji Line

The corridor it serves has long been a transport artery of eastern Osaka. From 1957 trolleybuses ran along Imazatosuji, linking with the Osaka city streetcar network to carry passengers between the eastern wards and the city centre, but as motor traffic grew the trolleybuses were withdrawn in 1969. City buses took over the route yet were dogged by congestion, and so a subway line was envisaged to connect the area with the radial rail network while running free of road traffic.

The plan took formal shape in the Transport Policy Council’s 10th report of 1989, which listed a line between Kami-Shinjō and Yuzato Rokuchōme as one that should be considered for future construction. Because underground obstructions were later found along the planned route, the northern starting point was moved in 1996 from Kami-Shinjō to Itakano, an area of Higashiyodogawa-ku whose population was rising on the back of new housing. A track-business licence for the Itakano–Imazato section was granted in 1999, and construction began in March 2000.

The line was built as an “iron-wheel linear-motor mini-subway.” Like the earlier Nagahori Tsurumi-ryokuchi Line, it uses linear-motor-driven trains running on standard-gauge (1,435 mm) track with a tunnel cross-section about 20 per cent smaller than that of conventional subway cars, electrified at 1,500 V DC by overhead line and worked by one-person (driver-only) operation. The smaller bore was intended to cut construction costs, and station and platform designs were deliberately standardised toward the same end — a marked contrast with the individually decorated stations of the bubble-era Nagahori Tsurumi-ryokuchi Line. The platforms were the first in the Osaka subway network to be fitted with movable platform-edge gates, about 1.3 m high and interlocked with the train doors.

Construction proved unusually difficult. To pass beneath existing subway lines and other buried structures the route runs at least 10 m below the streets for almost its whole length, and where it crosses the Neya River and the Second Neya River it dives past 30 m; the deepest point, about 37 m underground between Shigino and Midoribashi where it passes under the Second Neya River, is the deepest on the entire Osaka subway network. The line is also the second railway after the JR Tōzai Line — and the first subway — to tunnel beneath the Yodo River. The ground here is a soft, water-laden “super-soft clay” in which bulldozers often bogged down, and the alignment includes the tightest curve on any Osaka subway main line, a radius of just 83 m between Shimizu and Shimmori-Furuichi. As a result, although the mini-subway design cut overall costs by close to a third, building the Itakano–Imazato section still came to about ¥271.8 billion, around ¥22.5 billion per kilometre, against an originally projected ¥315.6 billion.

The Itakano–Imazato section, 11.9 km long, opened at noon on 24 December 2006, completing the line at its present length and making it the most recent addition to the Osaka subway. It was planned only as the first of two phases: a southward extension from Imazato to Yuzato Rokuchōme in Higashisumiyoshi-ku formed the intended second stage. Faced with the cost — the extension was reckoned to need a further ¥132 billion or so — Mayor Junichi Seki campaigned in the 2005 mayoral election on reviewing it, and on 28 November 2005, freshly re-elected, he froze the planned start and 2016 opening of the Imazato–Yuzato Rokuchōme section. With the city’s ridership well below the figures forecast for the line, that extension has since remained on hold.

On 1 April 2018 the Osaka municipal subway was corporatised: Osaka Metro Co., Ltd. succeeded the Osaka Municipal Transportation Bureau and the Imazatosuji Line became one of its routes. In place of the deferred rail extension, Osaka and Osaka Metro launched the Imazato Liner, a bus-rapid-transit service run as a social experiment to test demand for, and the feasibility of a rail alternative to, the southern extension; named by public vote in mid-2018, it began operating on 1 April 2019 as a five-year trial linking Imazato with the south-eastern parts of the city. The Imazatosuji Line continues to carry around 68,000 passengers a day, the lightest patronage of the network it joined.

• 1957Trolleybuses begin running along Imazatosuji, connecting with the Osaka streetcar network between the eastern wards and the city centre.
• 1969Trolleybus service on Imazatosuji is withdrawn as motor traffic grows; city buses take over the corridor.
• 1989The Transport Policy Council’s 10th report lists a Kami-Shinjō–Yuzato Rokuchōme line as one to be considered for future construction.
• 1996Following the discovery of underground obstructions, the northern starting point is moved from Kami-Shinjō to Itakano.
• 1999A track-business licence is granted for the Itakano–Imazato section.
• 20008 March: construction of the Imazatosuji Line begins.
• 200410 November: the line colour (golden orange) and the train design are decided.
• 200528 November: newly re-elected Mayor Junichi Seki freezes the planned start and 2016 opening of the Imazato–Yuzato Rokuchōme extension on fiscal grounds.
• 20066 July: the line’s name and station names are officially announced. 24 December: the Itakano–Imazato section (11.9 km) opens at noon, completing the line.
• 20181 April: the Osaka municipal subway is corporatised; Osaka Metro Co., Ltd. succeeds the Osaka Municipal Transportation Bureau and the line becomes one of its routes.
• 20191 April: the Imazato Liner bus-rapid-transit service begins as a five-year social experiment in place of the deferred southern extension, linking Imazato with the south-eastern parts of the city.