Aichi Loop Line

The corridor has its origins in the prewar railway-building programme. Under an amendment to the Railway Construction Act on 30 March 1927 a line "from Okazaki, Aichi Prefecture, through Koromo to Tajimi, Gifu Prefecture" was added to the schedule of planned lines as the Okata Line (岡多線). For routes judged hard to sustain, the Ministry of Railways established bus services ahead of building the railway, and on 20 December 1930 it opened the Okata Line bus between Okazaki and Tajimi — the very first government-run bus route — with seven buses and ten trucks. The railway itself was designated a survey line in 1957 and a construction line in 1959.

After the Japan Railway Construction Public Corporation (JRCC) was founded in 1964, the work passed to it, and the JRCC treated the southern Okata Line together with the separately planned Seto Line (瀬戸線, Seto–Inazawa) as a single ring it called the "Okata–Seto Line." Roadbed construction of the Okata Line between Okazaki and Toyota began on 13 August 1965. On 1 October 1970 the Okata Line opened as a line of Japanese National Railways between Okazaki and Kitano-Masuzuka (8.7 km), single-track and for freight only, primarily to carry finished cars from Toyota Motor's Kamigō plant.

Passenger service finally arrived on 26 April 1976, when the line was extended from Kitano-Masuzuka to Shin-Toyota (10.8 km) and began carrying passengers over the whole of the then-built single-track route. Even so, with few trains, early last departures and stiff competition from existing bus services, ridership lagged; by April 1981 the average traffic density was only about 2,757 passengers per day, below the 4,000-per-day threshold that marked a line for abandonment under the JNR reconstruction law. When Toyota's car-shipping traffic on the line ended at the close of 1984, the freight rationale fell away too, and JNR applied to abandon the Okazaki–Shin-Toyota section as a third-batch specified local line.

The outcome instead was conversion to a third sector. From 1983 JNR began studying the idea, and on 16 July 1984 it formally proposed to Aichi Prefecture and the four lineside cities — Okazaki, Toyota, Seto and Kasugai — that the whole Okata–Seto corridor (Okazaki–Kōzōji) be run by a third-sector company; building of the unbuilt Shin-Toyota–Kōzōji section was suspended in the meantime. After the local governments agreed on 19 August 1985 to accept the conversion, the company Aichi Loop Railway was incorporated on 19 September 1986, the JRCC resumed construction of the missing section, and the lease charges owed to the corporation were taken over after privatisation by the JNR Settlement Corporation so as not to burden the local side.

With the break-up and privatisation of JNR on 1 April 1987 the Okazaki–Shin-Toyota section passed to the Central Japan Railway Company (JR Central), with Japan Freight Railway (JR Freight) as a Type-2 operator between Okazaki and Kita-Okazaki. The transfer to the third sector then took place on 31 January 1988: JR Central's Okata Line was abolished and, the same day, the newly completed Shin-Toyota–Kōzōji section (25.8 km) opened, finally joining the two ends and bringing the full Aichi Loop Line into being. Many new stations opened with it, and daily train numbers were raised at a stroke from 26 to 72.

The new operator steadily upgraded the line. Capacity-enhancement works in two phases double-tracked several sections — Naka-Okazaki–Kita-Okazaki and Kitano-Masuzuka–Mikawa-Kamigō by December 2001 and Setoshi–Kōzōji by October 2004 — and on 1 September 2004 the maximum speed was raised to 110 km/h. The line's biggest moment came with Expo 2005 (the 2005 World Exposition, Aichi), whose main gateway was Yakusa Station; Yakusa was temporarily renamed "Banpaku-Yakusa" from 10 October 2004 until the fair closed on 30 September 2005. New stations at Aikan-Umetsubo and Kaizu opened on 1 March 2005, the same day the "Expo Shuttle" through-service from Nagoya over the JR Chūō Line began running, and the exposition year saw a record traffic density of 15,453 passengers per day.

After the fair, regular through-running with the JR Chūō Line to Nagoya was introduced from 1 October 2005. Responding to Toyota Motor's push to shift its workers from cars to public transport, the company double-tracked the Mikawa-Toyota–Shin-Toyota section — placed in service on 27 January 2008 — and from 15 March 2008 ran shuttle trains there at intervals of about eight minutes at peak times. The line later joined the nationwide IC-card network when TOICA became usable on 2 March 2019. Today the Aichi Loop Line remains a busy commuter railway, its traffic density holding above 9,000 passengers per day, carrying workers and students to the factories, offices and schools strung along the eastern arc of greater Nagoya.

• 192730 March: under an amendment to the Railway Construction Act, a line from Okazaki via Koromo to Tajimi (Gifu) is added to the planned-lines schedule as the Okata Line.
• 193020 December: the Ministry of Railways opens the Okata Line bus between Okazaki and Tajimi — the first government-run bus route — with seven buses and ten trucks.
• 196513 August: roadbed construction of the Okata Line between Okazaki and Toyota begins (under the Japan Railway Construction Public Corporation).
• 19701 October: the Okata Line opens as a JNR line between Okazaki and Kitano-Masuzuka (8.7 km), single-track and freight-only, chiefly to carry finished cars from Toyota's Kamigō plant.
• 19711 October: Kita-Okazaki Station opens (the former Kita-Okazaki signal post is upgraded to a station).
• 197626 April: the line is extended from Kitano-Masuzuka to Shin-Toyota (10.8 km) and passenger service begins over the whole then-built single-track route.
• 198416 July: JNR proposes to Aichi Prefecture and the four lineside cities (Okazaki, Toyota, Seto, Kasugai) that the Okata–Seto corridor be run by a third-sector company; Toyota's car-shipping traffic on the line ends at year's end.
• 198519 August: Aichi Prefecture and the four cities agree to accept conversion of the Okazaki–Kōzōji line to a third sector.
• 198627 May: the Okata Line (Okazaki–Shin-Toyota) is approved as a third-batch specified local line; 19 September: the company Aichi Loop Railway is incorporated.
• 19871 April: on the break-up and privatisation of JNR, the Okazaki–Shin-Toyota section passes to JR Central, with JR Freight as a Type-2 operator between Okazaki and Kita-Okazaki.
• 198831 January: JR Central's Okata Line is abolished and converted to the Aichi Loop Railway; the new Shin-Toyota–Kōzōji section (25.8 km) opens, completing the full line. Daily trains rise from 26 to 72.
• 200123 December: phase-1 capacity works are completed, double-tracking Naka-Okazaki–Kita-Okazaki (1.9 km) and Kitano-Masuzuka–Mikawa-Kamigō (2.0 km).
• 20041 September: the maximum speed is raised to 110 km/h. 3 October: phase-2 works double-track Setoshi–Kōzōji. 10 October: Yakusa Station is renamed 'Banpaku-Yakusa' for Expo 2005.
• 20051 March: Aikan-Umetsubo and Kaizu stations open, and the 'Expo Shuttle' through-service from Nagoya over the JR Chūō Line begins (to 30 September); the Expo year records a peak traffic density of 15,453 passengers/day. 1 October: regular through-running with the JR Chūō Line begins.
• 200827 January: the Mikawa-Toyota–Shin-Toyota section is double-tracked; 15 March: shuttle trains begin running there, giving roughly eight-minute peak intervals.
• 20192 March: the line becomes compatible with the TOICA IC card and the nationwide mutual-use IC-card network.