Aizu Kinugawa Line

The line threads a rugged, mountainous belt along the Tochigi–Fukushima prefectural border, almost all of it within Nikkō National Park. Its starting point at Shin-Fujiwara sits at an elevation of 425.3 metres, the terminus at Aizu-Kōgen-Ozeguchi at 722.5 metres, and the highest station, Ojika-Kōgen, at 759.7 metres. Because it was built by the Japan Railway Construction Public Corporation to a high standard, almost the entire route runs straight through tunnels, viaducts and bridges — 18 tunnels and 64 bridges in all — with no level crossings except one near Shin-Fujiwara and the platform crossings at the end stations. As a result, even an all-stations train covers the line in about 35 minutes at a scheduled speed near 50 km/h, comparable to a railway on flat ground.

The line's origins lie in a planned route listed in the schedule of the amended Railway Construction Act. It formed part of item No. 33, "a railway from Imaichi in Tochigi Prefecture via Takatoku to Tajima in Fukushima Prefecture," and was conceived as a section of the wider Yaganu Line scheme, which would have joined the Tōhoku Main Line and the Ōu Main Line by linking through the Aizu Line, Tadami Line and other routes to connect Yonezawa in Yamagata with Koga in Ibaraki. The planned line was registered in the schedule in April 1922, advanced to a survey line in 1957 and a construction line in 1962, and was designated a Japan Railway Construction Public Corporation construction line in 1964.

Construction proceeded from the north as the Corporation's Yagan Line, with the Imaichi–Fujiwara portion dropped because it would have competed with the Tōbu Kinugawa Line. Authorisations followed section by section — the 9.9-kilometre Takinohara–Kamimiyori stretch in May 1966, then further segments through 1980 — and most of the railway's structures, including its bridges and tunnels, were completed. Work was then frozen under the JNR Reconstruction Act. Local authorities determined to see the railway opened nonetheless agreed on third-sector operation; the newly formed Yagan Railway took the project over, and because the line had been built without electrification, an additional electrification programme was carried out so that it could connect with and run through to the Tōbu Kinugawa Line at Shin-Fujiwara.

Yagan Railway Co., Ltd. was established on 20 November 1981. Electrification was approved by the Ministry of Transport and the Ministry of Finance in 1984; the line name "Aizu Kinugawa Line" was chosen by public solicitation in the spring of 1985; and the station names were settled in August 1985. The line opened on 9 October 1986 between Shin-Fujiwara and Aizu-Kōgen (now Aizu-Kōgen-Ozeguchi), a distance of 30.7 km, with through services to and from the Tōbu Railway beginning the same day. In its first year the line carried 611,000 passengers.

On 12 October 1990, following electrification of the Aizu-Kōgen–Aizu-Tajima section of the Aizu Railway Aizu Line, through services with the Aizu Line began, extending trains north toward Aizu-Tajima. Premium services evolved over the following years: a reserved-seat rapid express was introduced in 1988 and the express "Minami-Aizu" in 1991, before that express was withdrawn in 2005 and replaced by the rapid "AIZU Mount Express," which began running through the line. On 18 March 2006 the nickname "Hot Spa Line" was adopted to publicise the many hot-spring resorts along the route, and several stations were renamed, including Nakamiyori to Nakamiyori-Onsen, Kamimiyori-Shiobara to Kamimiyori-Shiobara-Onsenguchi, and Aizu-Kōgen to Aizu-Kōgen-Ozeguchi.

The line has twice been disrupted by natural events. On 14 March 2011 its mutual through services with the Tōbu lines and the Aizu Railway Aizu Line were suspended because of the rolling blackouts that followed the 2011 Tōhoku earthquake, resuming on 20 March. Then, on 10 September 2015, the whole line was closed after the Kantō–Tōhoku heavy rains caused a power failure — when a Tokyo Electric Power transmission tower tilted — and brought landslide debris onto the track in places. Service was restored in stages: between Shin-Fujiwara and Kamimiyori-Shiobara-Onsenguchi on 18 September, across the whole line (with the northern section worked by diesel cars) on 19 September, and finally by electric trains on the Kamimiyori-Shiobara-Onsenguchi–Aizu-Kōgen-Ozeguchi section on 11 December 2015.

On 21 April 2017 the limited express "Revaty Aizu," using Tōbu 500 series "Revaty" trains, began running through the line between Asakusa and Aizu-Tajima. A timetable revision on 12 March 2022 cut the line's services from seventeen to ten trains in each direction as tourist demand fell. Today the Aizu Kinugawa Line is overwhelmingly a leisure railway: most of its passengers are non-commuters from Tokyo and its suburbs travelling through on the Tōbu network to visit the hot springs and highlands along the way, while commuter and student season-ticket use is very small. Local trains run within the line, and through trains continue to link it with the Tōbu Kinugawa Line to the south and the Aizu Railway Aizu Line to the north.

• 1922April: the route (the Yagan Line) is registered as a planned line in the schedule of the amended Railway Construction Act.
• 1964April: the planned line — having become a survey line in 1957 and a construction line in 1962 — is designated a Japan Railway Construction Public Corporation construction line.
• 19667 May: construction of the 9.9 km Takinohara–Kamimiyori (now Kamimiyori-Shiobara-Onsenguchi) section is authorised, the first of the line's segments.
• 198120 November: Yagan Railway Co., Ltd. is established as a third-sector company to take over the construction frozen under the JNR Reconstruction Act.
• 1984May: electrification of the line, built without electrification, is approved by the Ministry of Transport and the Ministry of Finance.
• 1985Spring: the line name 'Aizu Kinugawa Line' is chosen by public solicitation; the station names are settled that August.
• 19869 October: the Shin-Fujiwara–Aizu-Kōgen (now Aizu-Kōgen-Ozeguchi) section, 30.7 km, opens; through services with the Tōbu Railway begin the same day.
• 198819 October: Shimotsuke-Kamimiyori Station is renamed Kamimiyori-Shiobara; a reserved-seat rapid express service is introduced.
• 199012 October: following electrification of the Aizu-Kōgen–Aizu-Tajima section of the Aizu Railway Aizu Line, through services with that line begin.
• 199121 July: the express 'Minami-Aizu' is introduced, with its own express fare.
• 20051 March: the express 'Minami-Aizu' is withdrawn and the rapid 'AIZU Mount Express' begins through running over the line.
• 200618 March: the nickname 'Hot Spa Line' comes into use and several stations are renamed, including Aizu-Kōgen to Aizu-Kōgen-Ozeguchi.
• 201114 March: mutual through services with the Tōbu lines and the Aizu Railway Aizu Line are suspended owing to rolling blackouts after the Tōhoku earthquake; they resume on 20 March.
• 201510 September: the Kantō–Tōhoku heavy rains close the whole line; service is restored in stages, with electric running on the northern section resuming on 11 December.
• 201721 April: the limited express 'Revaty Aizu', using Tōbu 500 series trains, begins through running between Asakusa and Aizu-Tajima.
• 202212 March: a timetable revision cuts the line's services from seventeen to ten trains in each direction amid falling tourist demand.