Kyūdai Main Line

The line was built from both ends over nearly two decades, and its eastern portion began life as a private railway. On 30 October 1915 the Daitō Railway (大湯鉄道) opened the first section, from Ōita-shi Station to Onoya, near the Ōita end. The company was bought out and nationalised on 1 December 1922, and the Ōita–Onoya section became the government-run Daitō Line (大湯線). Extensions westward up the Ōita River valley followed in stages: Onoya to Yunohira in 1923, Yunohira to Kita-Yufu in 1925, Kita-Yufu to Noya in 1926, Noya to Bungo-Nakamura in 1928, Bungo-Nakamura to Bungo-Mori in 1929, and Bungo-Mori to Kita-Yamada in 1932. On 29 September 1933 the Daitō Line was extended from Kita-Yamada to Amagase.

Construction from the Kurume end proceeded separately as the Kyūdai Line (久大線). The first stretch, from Kurume to Chikugo-Yoshii, opened on 24 December 1928, and was pushed eastward in further stages — to Chikugo-Ōishi in 1931, to Yoake in March 1932 and to Hita in March 1934. On 15 November 1934 the final gap, from Hita to Amagase, was closed; on the same day the Daitō Line (Ōita–Amagase) was merged into the Kyūdai Line, completing a continuous through route across Kyūshū between Kurume and Ōita. With the opening of the connecting Miyanoharu Line on 27 June 1937, the through line was promoted to trunk-line status and renamed the Kyūdai Main Line (久大本線).

In the postwar decades the line settled into its role as a cross-island route worked by diesel railcars. Kita-Yufu Station was renamed Yufuin in 1950. In June 1953 the line was devastated by the great western Japan flood and closed, reopening that August. Steam haulage ended in 1970, and centralised traffic control (CTC) was commissioned across the whole line in two stages in early 1984. All freight operations were abolished on 1 April 1987, the day the Japanese National Railways were broken up and privatised and the Kyūdai Main Line passed to the newly formed JR Kyushu.

Under JR Kyushu the line developed a strong tourist profile. In 1988 it was given the nickname “Yufu Kōgen Line,” and the maximum line speed was raised to 95 km/h in 1992. The Yufuin no Mori, a distinctive green tourist express introduced by JR Kyushu, runs from Hakata via Kurume to the resort town of Yufuin, alongside the regular “Yufu” limited expresses. The line once had branches at two intermediate points — the Hitahikosan Line diverged at Yoake and the Miyanoharu Line at Era — but the Miyanoharu Line was abolished on 1 December 1984, and after the Hitahikosan Line was converted to a bus-rapid-transit operation (the Hitahikosan Line BRT) on 28 August 2023, the Kyūdai Main Line was left with no branching railway. As a result it is, apart from the Kyushu Shinkansen, the longest conventional railway line in Kyūshū with no junction along its course.

Running through mountainous, river-hugging country, the line has been repeatedly cut by flooding. In July 2012 the Northern Kyushu heavy rains damaged the Chikugo-Yoshii–Hita section — washing out roadbed and sinking a railway-bridge pier — and severed the Kurume–Hita stretch; the whole line was restored by 25 August 2012. The most serious blow came on 5 July 2017, when the Northern Kyushu heavy rains swept away the bridge over the Kagetsu River between Teruoka and Hita, closing the central part of the line and forcing replacement bus services. The Kagetsu River bridge was rebuilt and the entire Kyūdai Main Line reopened on 14 July 2018, almost a year after the disaster. Further heavy-rain disruptions in July 2020, August 2021 and July 2023 again interrupted services for a time before the line was restored each time.

• 191530 October: the Daitō Railway opens the first section, Ōita-shi–Onoya, near the Ōita end of the future line.
• 19221 December: the Daitō Railway is bought out and nationalised; Ōita–Onoya becomes the government-run Daitō Line.
• 192329 September: the Daitō Line is extended from Onoya to Yunohira.
• 192824 December: the Kyūdai Line opens at the Kurume end, from Kurume to Chikugo-Yoshii.
• 193329 September: the Daitō Line reaches Amagase, completing its westward extension from the Ōita end.
• 193415 November: the Hita–Amagase gap is closed and the Daitō Line is merged into the Kyūdai Line, completing the through route across Kyūshū between Kurume and Ōita.
• 193727 June: with the opening of the connecting Miyanoharu Line, the Kyūdai Line is promoted to trunk status and renamed the Kyūdai Main Line.
• 195326 June: the line is devastated by the great western Japan flood and closed; it reopens on 8 August.
• 1970Steam-locomotive operation on the line ends (dieselisation).
• 1984Centralised traffic control (CTC) is commissioned over the whole line in two stages (Amagase–Ōita on 20 January, Kurume–Bungo-Miyoshi on 15 February).
• 19871 April: all freight operations are abolished and, on the privatisation of Japanese National Railways, the line passes to JR Kyushu.
• 198815 March: the line is given the nickname “Yufu Kōgen Line.”
• 199215 July: the maximum line speed is raised to 95 km/h.
• 2012July: the Northern Kyushu heavy rains cut the Kurume–Hita section; the whole line is restored by 25 August.
• 20175 July: the Northern Kyushu heavy rains wash away the Kagetsu River bridge between Teruoka and Hita, closing the central part of the line.
• 201814 July: the rebuilt Kagetsu River bridge reopens and the entire Kyūdai Main Line returns to service, almost a year after the washout.