Hitahikosan Line

The present line was assembled in 1960 from several older railways, the oldest stretches of which date to the late nineteenth century. On the Tagawa side, the Hōshū Railway opened a line from Ita (now Tagawa-Ita) toward Gotōji (now Tagawa-Gotōji) on 5 February 1896, and extended it from Gotōji to Kawasaki on 10 July 1899. That company was absorbed by the Kyushu Railway on 3 September 1901, which carried the line on to Soeda on 21 December 1903. The Kyushu Railway was nationalised on 1 July 1907 under the Railway Nationalization Act, and the route became part of the government's Tagawa Line.

The northern half of the corridor was the work of the Kokura Railway, which on 1 April 1915 opened a line of 24.5 miles from Higashi-Kokura through Kami-Kōharu (now Kawara) to Kami-Soeda. This private railway was bought out under wartime nationalisation on 1 May 1943 and became the first Soeda Line. Meanwhile a separate Hikosan Line was pushed up from the Hita end, opening from Yoake to Hōshuyama on 22 August 1937 and reaching Daigyōji via Hōshuyama on 20 September 1946; from the Tagawa end the Nishi-Soeda–Hikosan section opened on 25 August 1942.

Closing the final gap proved costly. During construction of the 4,380-metre Shakadake Tunnel between Chikuzen-Iwaya and Hikosan, a roof-fall on 19 March 1953 killed twenty-one workers. The Hikosan–Daigyōji section finally opened on 15 March 1956, completing a through route that was consolidated as the Hita Line. Later that year, on 19 November 1956, a new link between Jōno and Ishida allowed the line's trains to run directly into Kokura, while the old Higashi-Kokura–Ishida stretch became freight-only. A short Kawara–Ita branch opened on 1 October 1957, completing the route used today.

On 1 April 1960 the Hita Line, the Ita–Soeda portion of the Tagawa Line and associated freight branches were merged to form the Hitahikosan Line, running from Jōno through Gotōji to Yoake, a distance of 68.7 km; at the same time the Kawara–Ōtō–Soeda section was split off as the second Soeda Line, which was abolished in 1985. Because the line was a shortcut from Moji and Kokura toward Yufuin on the Kyūdai Main Line, it carried semi-express and express trains such as the Asagiri, Akiyoshi, Handa, Hita and Hikosan from the 1960s into the 1980s. As Kitakyushu's industry declined, passenger flows between western Ōita and the Fukuoka area thinned, and the opening of the Ōita Expressway drew traffic to road, those express services were progressively downgraded from 1980.

The line then settled into a quiet regional existence. Whole-line centralised traffic control was introduced on 15 February 1984, and on 3 November 1982 Ita and Gotōji had been renamed Tagawa-Ita and Tagawa-Gotōji. Freight service ceased between Tagawa-Gotōji and Yoake on 1 November 1986 and was eliminated entirely by 1999. When Japanese National Railways was privatised on 1 April 1987, the line passed to JR Kyushu, which has operated it ever since with diesel railcars.

The line's southern reaches were broken by disaster on 5 July 2017, when the torrential rain of Severe Tropical Storm Nanmadol — the July 2017 Northern Kyūshū floods — damaged the track at sixty-three locations between Soeda and Yoake, washing out bridges and embankments and suspending all service south of Soeda. After years of negotiation over restoration costs, JR Kyushu, the prefectures of Fukuoka and Ōita and the line's municipalities agreed on 16 July 2020 not to rebuild the section as railway but to replace it with bus rapid transit, with a dedicated busway built between Hikosan and Hōshuyama.

The replacement BRT Hikoboshi Line opened on 28 August 2023, running by bus between Soeda and Hita and operated by JR Kyushu Bus; it was Japan's third rail service to be converted to BRT, after JR East's Ōfunato and Kesennuma Lines. The Hitahikosan Line thus survives as a railway only between Jōno (with through running to Kokura) and Soeda, the Soeda–Yoake section continuing as a bus route. On 26 December 2025 JR Kyushu filed to formally abolish the railway business over the Soeda–Yoake section, with abolition scheduled for 31 March 2027.

• 18965 February: the Hōshū Railway opens Ita (later Tagawa-Ita) to Gotōji (later Tagawa-Gotōji).
• 189910 July: the Hōshū Railway extends the line from Gotōji to Kawasaki, an early coal-traffic segment of the future route.
• 19013 September: the Hōshū Railway is merged into the Kyushu Railway.
• 190321 December: the Kyushu Railway extends the line from Kawasaki to Soeda.
• 19071 July: the Kyushu Railway is nationalised under the Railway Nationalization Act; the route becomes part of the Tagawa Line.
• 19151 April: the Kokura Railway opens Higashi-Kokura through Kami-Kōharu (now Kawara) to Kami-Soeda (24.5 miles), the corridor's northern half.
• 193722 August: the Hikosan Line opens from Yoake to Hōshuyama, advancing from the Hita end.
• 19431 May: the Kokura Railway is taken over under wartime nationalisation, becoming the first Soeda Line.
• 195319 March: during construction of the 4,380 m Shakadake Tunnel (Chikuzen-Iwaya–Hikosan), a roof-fall kills 21 workers.
• 195615 March: the Hikosan–Daigyōji section opens, completing the through route, which is consolidated as the Hita Line.
• 19571 October: the Kawara–Ita branch (4.0 km) opens, completing the route in use today.
• 19601 April: the Hita Line, the Ita–Soeda part of the Tagawa Line and freight branches are merged to form the Hitahikosan Line (Jōno–Gotōji–Yoake, 68.7 km); the Kawara–Ōtō–Soeda section is split off as the second Soeda Line.
• 19823 November: Ita Station is renamed Tagawa-Ita and Gotōji Station is renamed Tagawa-Gotōji.
• 198415 February: centralised traffic control (CTC) is introduced over the whole line.
• 19861 November: freight service ceases between Tagawa-Gotōji and Yoake (freight was eliminated entirely by 1999).
• 19871 April: Japanese National Railways is privatised; the line is succeeded by JR Kyushu.
• 20175 July: the July 2017 Northern Kyūshū floods (Severe Tropical Storm Nanmadol) damage the track at 63 locations between Soeda and Yoake; service south of Soeda is suspended.
• 202016 July: JR Kyushu, Fukuoka and Ōita prefectures and the line's municipalities agree to replace the Soeda–Yoake section with bus rapid transit, with a dedicated busway between Hikosan and Hōshuyama.
• 202328 August: the replacement BRT Hikoboshi Line opens between Soeda and Hita, operated by JR Kyushu Bus — Japan's third rail-to-BRT conversion after JR East's Ōfunato and Kesennuma Lines.
• 202526 December: JR Kyushu files to abolish the railway business over the Soeda–Yoake section, with abolition scheduled for 31 March 2027.