Ōito Line

The line was built in three originally separate pieces. The southern portion, between Matsumoto and Shinano-Ōmachi, was constructed by the Shinano Railway (信濃鉄道, Shinano Tetsudō) — a private company unrelated to the present-day Shinano Railway — which opened its first stretch, from Matsumoto-shi Station (the present Kita-Matsumoto) to Toyoshina, on 6 January 1915. Over the following months the company extended the line step by step, reaching Shinano-Ōmachi by 2 November 1915, and in 1916 it pushed south into Matsumoto Station and began passenger services there.

The rest of the route was built by the state. Construction of the Ōito South Line (大糸南線) northward from Shinano-Ōmachi began on 25 September 1929, while the separate Ōito North Line (大糸北線) was opened from Itoigawa to Nechi on 14 November 1934 and extended to Kotaki the following year. The line takes its name from this state project to join Shinano-Ōmachi (大町) and Itoigawa (糸魚川), one character drawn from each place name. On 1 June 1937 the Shinano Railway's Matsumoto–Shinano-Ōmachi section was nationalised and absorbed into the government railway.

Electrification spread gradually through the southern half. The Shinano Railway had already electrified the Matsumoto–Shinano-Ōmachi section at 1,500 V DC on 8 January 1926. After nationalisation the overhead wire was pushed north in stages — to Shinano-Yotsuya (the present Hakuba) on 17 July 1959, on to Shinano-Moriue on 20 July 1960, and finally from Shinano-Moriue to Minami-Otari on 20 December 1967 — each extension driven by the growth of tourism along the line. The northern, JR West portion beyond Minami-Otari was never electrified.

The long-isolated North and South lines were finally joined on 15 August 1957, when the Nakatsuchi–Kotaki segment opened. With this through connection the whole Matsumoto–Itoigawa route was completed, the Ōito North Line and the newly built section were merged into the Ōito South Line, and the combined line was renamed the Ōito Line. Steam haulage gave way to diesel railcars on the southern half by the early 1960s, and over the following decades the line saw colour-light signalling replace semaphores and limited expresses such as the Azusa and Shinano begin running onto it.

Centralised traffic control (CTC) was commissioned over the whole line on 25 March 1983. Following the privatisation of Japanese National Railways on 1 April 1987, the line was divided: JR East took over the Matsumoto–Minami-Otari section and JR West the Minami-Otari–Itoigawa section, while Japan Freight Railway became a freight operator over Matsumoto–Shinano-Ōmachi and freight services north of Shinano-Ōmachi were discontinued. The mountainous corridor along the Himekawa proved vulnerable to natural disasters: a major flood on 11 July 1995 severed the line north of Shinano-Ōmachi, and the damaged Minami-Otari–Kotaki section was not fully restored until 29 November 1997. The earthquake of 22 November 2014, on the Kamishiro Fault, again cut the line, with full restoration on 7 December 2014.

The opening of the Hokuriku Shinkansen between Nagano and Kanazawa in 2015 reshaped the line's northern context. The parallel Hokuriku Main Line through Itoigawa was separated from JR West and transferred to the third-sector Echigo Tokimeki Railway, leaving the JR West portion of the Ōito Line with no connection to the rest of the JR West conventional network — an isolated branch reached only via JR East and the third-sector line. JR East introduced station numbering on its section from 12 December 2016, numbering the stations in sequence from 9 at Minami-Otari to 42 at Matsumoto. With ridership on the non-electrified northern section in long decline, JR West announced on 3 February 2022 that it would open discussions with local governments about the future of the Minami-Otari–Itoigawa section, including possible conversion to bus services.

• 19156 January: the Shinano Railway opens its first segment, Matsumoto-shi (present Kita-Matsumoto) to Toyoshina; the line reaches Shinano-Ōmachi on 2 November.
• 191618 September: passenger services begin on the Matsumoto–Kita-Matsumoto section, bringing the line into Matsumoto Station.
• 19268 January: the Shinano Railway electrifies the Matsumoto–Shinano-Ōmachi section at 1,500 V DC.
• 192925 September: the state-built Ōito South Line opens its first section, Shinano-Ōmachi–Yanaba.
• 193414 November: the separate Ōito North Line opens between Itoigawa and Nechi.
• 19371 June: the Shinano Railway's Matsumoto–Shinano-Ōmachi section is nationalised and absorbed into the government railway.
• 195715 August: the Nakatsuchi–Kotaki segment opens, completing the through route; the North Line and new section are merged into the South Line and the whole route is renamed the Ōito Line.
• 195917 July: electrification is extended from Shinano-Ōmachi to Shinano-Yotsuya (present Hakuba).
• 196720 December: electrification reaches Minami-Otari (Shinano-Moriue–Minami-Otari), completing electrification of the Matsumoto–Minami-Otari section.
• 198325 March: centralised traffic control (CTC) is commissioned over the whole line.
• 19871 April: on the privatisation of JNR, the line is divided between JR East (Matsumoto–Minami-Otari) and JR West (Minami-Otari–Itoigawa); JR Freight becomes a freight operator on Matsumoto–Shinano-Ōmachi and freight north of Shinano-Ōmachi is discontinued.
• 199511 July: a major flood severs the line north of Shinano-Ōmachi; the damaged Minami-Otari–Kotaki section is not fully restored until 29 November 1997.
• 19988 December: E127 series electric railcars enter service on the JR East section.
• 201422 November: the Kamishiro Fault earthquake cuts the line between Shinano-Ōmachi and Itoigawa; full restoration follows on 7 December.
• 201612 December: JR East introduces station numbering on its section, numbering stations in sequence from 9 (Minami-Otari) to 42 (Matsumoto).
• 20223 February: JR West announces it will begin discussions with local governments about the future of the Minami-Otari–Itoigawa section, including possible conversion to bus services.