Tazawako Line

The present line was assembled from two separate light railways built from opposite ends. From the Morioka side, the Hashiba Light Line (橋場軽便線) opened first, between Morioka and Shizukuishi, on 25 June 1921, and was extended onward to Hashiba on 15 July 1922. From the Ōmagari side, the Obonai Light Line (生保内軽便線) opened between Ōmagari and Kakunodate on 30 July 1921. On 2 September 1922 the two were redesignated the Hashiba Line and the Obonai Line respectively.

Both lines were then pushed gradually toward each other through the mountains. The Obonai side reached Jindai in December 1921 and Obonai (the future Tazawako) in August 1923, while the Hashiba side gained its Shizukuishi–Akabuchi segment in September 1964. The Hashiba branch beyond Shizukuishi had meanwhile fallen out of use: the Shizukuishi–Hashiba section was suspended in 1944 and never reopened.

The through route was finally completed on 20 October 1966, when the 18.1-kilometre Akabuchi–Tazawako section opened on completion of the 3,915-metre Sengan Tunnel beneath the Ōu range. On the same day the Obonai Line was absorbed and the unified route was renamed the Tazawako Line; Obonai Station itself had been renamed Tazawako three weeks earlier, on 1 October 1966.

Under Japanese National Railways the line was modernised over the following decades. Diesel railcar operation had begun in 1961, and steam working ended with the line's completion in 1966. Freight services were abolished on 1 April 1982, and on 15 November 1982 the whole line was electrified at 20 kV 50 Hz AC. With the breakup and privatisation of JNR on 1 April 1987, the Tazawako Line passed to the newly formed East Japan Railway Company (JR East).

The line's character was transformed by the Akita Shinkansen project. On 30 March 1996 the entire line was closed and replaced by substitute buses while it was regauged, and on 22 March 1997 it reopened converted from 1,067 mm narrow gauge to 1,435 mm standard gauge. That same day the standard-gauge limited express Komachi began running through from Tōkyō, reaching Akita by reversing direction at Ōmagari and continuing over the Ōu Main Line; conventional local trains on the line were switched to standard-gauge electric multiple units, mostly with one-person operation.

Since the conversion the Tazawako Line has carried the frequent Komachi services alongside its local trains. Maegata Station opened between Morioka and Ōkama on 18 March 2023, and IC-card (Suica) use began on the Morioka–Shizukuishi section on 27 May 2023, bringing the line's station count to eighteen.

• 192125 June: the Hashiba Light Line opens between Morioka and Shizukuishi (16.0 km) on the Morioka side.
• 192130 July: the Obonai Light Line opens between Ōmagari and Kakunodate (16.8 km) on the Ōmagari side; extended to Jindai on 11 December.
• 19222 September: the two lines are renamed the Hashiba Line and the Obonai Line; the Hashiba side reaches Hashiba on 15 July.
• 192331 August: the Obonai Line is extended from Jindai to Obonai (the future Tazawako), 12.7 km.
• 19441 October: the Shizukuishi–Hashiba section (7.7 km) is suspended; it never reopens.
• 19611 July: diesel railcar operation begins on the line.
• 196410 September: the Shizukuishi–Akabuchi section (6.0 km) is completed and incorporated into the Hashiba Line.
• 196620 October: the 18.1 km Akabuchi–Tazawako section opens on completion of the 3,915 m Sengan Tunnel, finishing the through route; the Obonai Line is absorbed and the whole line is renamed the Tazawako Line. (Obonai Station had been renamed Tazawako on 1 October.)
• 19821 April: freight services are abolished on the whole line; 15 November: the entire line is electrified at 20 kV 50 Hz AC.
• 19871 April: with the breakup and privatisation of Japanese National Railways, the line passes to the East Japan Railway Company (JR East).
• 199116 March: the line's maximum speed is raised from 95 km/h to 110 km/h.
• 199630 March: the entire line is closed for regauging work and replaced by substitute buses.
• 199722 March: the line reopens regauged from 1,067 mm to 1,435 mm standard gauge; the standard-gauge limited express Komachi begins through service from Tōkyō (reversing at Ōmagari and continuing to Akita via the Ōu Main Line), and most local trains switch to one-person operation.
• 202318 March: Maegata Station opens between Morioka and Ōkama; 27 May: Suica IC-card use begins on the Morioka–Shizukuishi section.