Aoimori Railway Line

The corridor is far older than the company that now runs it. It was built by Nippon Railway, Japan's first private railway, and the (Morioka–)Metoki–Aomori section opened on 1 September 1891, completing a through route from Tokyo to Aomori. Stations were added along the new line in the following years, including Shimoda in December 1891 and the predecessor of Misawa Station (then Komagi) in 1894. When Nippon Railway was nationalised on 1 November 1906 the line passed into state hands, and on 12 October 1909 it was formally designated part of the Tōhoku Main Line under the national line-naming scheme.

Under state and then Japanese National Railways (JNR) ownership the line was steadily upgraded. New stations and signal posts opened through the early twentieth century, and the route around Aomori was progressively double-tracked from the 1920s onward. A major modernisation campaign in the 1960s saw the line double-tracked section by section until the whole Metoki–Aomori stretch was twin-tracked by 5 August 1968; on 21 July 1968 the alignment between Nonai and Aomori was rerouted onto a new line and Higashi-Aomori Station opened, while the old-line stations of Namiuchi and Uramachi closed. Electrification at 20 kV 50 Hz AC reached the line on 22 August 1968, and centralised traffic control (CTC) followed on 27 December 1976.

With the privatisation and break-up of JNR on 1 April 1987, the line came under the East Japan Railway Company (JR East). Its future, however, had already been tied to the Tōhoku Shinkansen. A 1990 government-and-ruling-party accord made it a condition that the conventional lines running parallel to newly authorised Shinkansen sections would be separated from JR at the time the Shinkansen opened. The Governor of Aomori agreed in 1991 to the separation of the Tōhoku Main Line as far as Hachinohe, and in 1998, after consulting the municipalities north of Hachinohe, agreed to the separation of the Hachinohe–Aomori section as well. The Aoimori Railway Company was formally incorporated on 30 May 2001.

The transfer happened in two stages, each tied to a northward extension of the Tōhoku Shinkansen. When the Shinkansen reached Hachinohe on 1 December 2002, the parallel conventional line was split off from JR East: the portion in Iwate Prefecture became the IGR Iwate Galaxy Railway Line, and the 25.9 km from Metoki on the Aomori-prefecture border to Hachinohe opened as the Aoimori Railway Line. Fares on the new section were set about 1.49 times the former JR East level, and the Aoimori 701 series electric multiple units entered service. The asset boundary with the Iwate Galaxy Railway lies at the prefectural border just south of Metoki Station.

The second stage followed the Shinkansen's extension to Shin-Aomori on 4 December 2010, when the remaining 96.0 km from Hachinohe to Aomori was transferred from JR East and incorporated into the Aoimori Railway Line, completing the present 121.9 km route; fares on this section were raised to about 1.37 times the former JR East level. The 2011 Tōhoku earthquake on 11 March suspended the whole line; Nonai Station was relocated the next day to coincide with the move of a nearby prefectural technical high school, and full operation resumed on 17 March 2011.

Since the takeover the line has seen modest expansion and the loss of its long-distance traffic. On 15 March 2014 the Aoimori 703 series entered service and Tsutsui Station opened between Higashi-Aomori and Aomori. The opening of the Hokkaidō Shinkansen on 26 March 2016 ended the last sleeper limited expresses that had run over the line, the Cassiopeia having made its final run that month. Today all Aoimori Railway trains are local services calling at every station, with no trains starting or terminating at Metoki — they run through to and from Morioka over the Iwate Galaxy Railway Line. JR East has used the Hachinohe–Noheji portion for its own through services, including the Shimokita rapid to the Ōminato Line and, until 2023, the Resort Asunaro sightseeing train, while JR Freight continues to carry freight along the corridor.

• 18911 September: Nippon Railway opens the (Morioka–)Metoki–Aomori section, completing the Tokyo–Aomori through route (Metoki Station itself not yet open).
• 19061 November: Nippon Railway is nationalised; the line becomes part of the state railway system.
• 190912 October: under the national line-naming scheme, the line is formally designated part of the Tōhoku Main Line.
• 19481 October: Metoki Signal Box is converted to a station, and Metoki Station opens — later the line's southern terminus.
• 19491 June: with the enactment of the Japanese National Railways Law, the line passes to Japanese National Railways (JNR).
• 19685 August: double-tracking of the entire Metoki–Aomori stretch is completed (the Nonai–Aomori realignment opening Higashi-Aomori Station on 21 July). 22 August: the line is electrified at 20 kV 50 Hz AC.
• 197627 December: centralised traffic control (CTC) is introduced over the line.
• 19871 April: with the privatisation and break-up of JNR, the line passes to the East Japan Railway Company (JR East).
• 19919 July: the Governor of Aomori agrees to separate the Tōhoku Main Line as far as Hachinohe from JR when the Shinkansen opens.
• 200130 May: the Aoimori Railway Company is formally incorporated.
• 20021 December: as the Tōhoku Shinkansen reaches Hachinohe, the Metoki–Hachinohe section (25.9 km) opens as the Aoimori Railway Line; the Iwate-prefecture portion becomes the IGR Iwate Galaxy Railway Line. Fares rise to ~1.49× the former JR East level and the Aoimori 701 series enters service.
• 20104 December: as the Tōhoku Shinkansen extends to Shin-Aomori, the Hachinohe–Aomori section (96.0 km) is transferred from JR East into the Aoimori Railway Line, completing the present 121.9 km route; fares on this section rise to ~1.37× the former JR East level.
• 201111 March: the Tōhoku earthquake suspends the whole line; Nonai Station is relocated on 12 March, and full service resumes on 17 March.
• 201415 March: the Aoimori 703 series enters service and Tsutsui Station opens between Higashi-Aomori and Aomori.
• 201626 March: with the opening of the Hokkaidō Shinkansen, the last sleeper limited expresses over the line end (the Cassiopeia having made its final run that month).