Dōnan Isaribi Railway Line

The corridor began as a state-built light railway. On 15 September 1913 the government railways opened the Kamiiso Light Railway (上磯軽便線) between Goryōkaku and Kamiiso, a stretch of about 8.8 km. The short line was redesignated the Kamiiso Line (上磯線) on 2 September 1922, and over the following years it was pushed steadily southwest along the coast toward the town of Esashi.

The extension came in three stages. The section from Kamiiso to Kikonai (29.0 km) opened on 25 October 1930; Kikonai to Yunotai (21.4 km) followed on 10 December 1935; and on 10 November 1936 the final stretch from Yunotai to Esashi (20.7 km) opened, completing a through route from Goryōkaku to Esashi. At that moment the whole line was renamed the Esashi Line (江差線).

For the rest of the twentieth century the Esashi Line was a Japanese National Railways (JNR) route. When JNR was divided and privatised on 1 April 1987, the Hokkaido Railway Company (JR Hokkaido) succeeded to the whole line as the first-class railway operator. The Goryōkaku–Kikonai section in particular grew in importance beyond its modest local traffic, because it lay on the approach to the Seikan Tunnel and the Kaikyō Line, the undersea route linking Hokkaidō with Honshū that opened in 1988. Limited-express trains such as the Hakuchō and Super-Hakuchō, together with the overnight Hamanasu, ran over the Goryōkaku–Kikonai tracks as part of the Tsugaru-Kaikyō corridor between Aomori and Hakodate.

The far end of the Esashi Line, however, was lightly used and unprofitable. On 12 May 2014 JR Hokkaido closed the Kikonai–Esashi section (42.1 km) to all traffic, ending rail service to Esashi and leaving the Goryōkaku–Kikonai segment as the surviving part of the line.

The decisive change came with the Hokkaido Shinkansen. When the Shinkansen opened from Shin-Aomori to Shin-Hakodate-Hokuto on 26 March 2016, the parallel conventional Goryōkaku–Kikonai section (37.8 km) was transferred from JR Hokkaido to the newly established South Hokkaido Railway Company and renamed the Dōnan Isaribi Railway Line. It was the first conversion of a JR line to third-sector operation in Hokkaidō since the closure of the Furusato Ginga Line in 2006. Just before the handover, on 22 March 2016, the overhead wire in the Kikonai area was raised to 25 kV to match the higher voltage used where the route meets the Shinkansen and the Kaikyō Line. For passengers the new operator runs former-JR KiHa 40 diesel railcars.

Although it is a small local railway, the Dōnan Isaribi Railway Line remains a vital freight artery. After the transfer JR Freight continued to operate over the entire line as a second-class railway operator, and the line carries a heavy flow of container freight trains hauled by EH800 electric locomotives based at the Goryōkaku depot, connecting onward via the Kaikyō Line and the Seikan Tunnel to Honshū. This freight role, rather than its sparse passenger service, is the line's principal reason for being and ties it directly to the national rail link between Hokkaidō and the rest of Japan.

• 191315 September: the state railways open the Kamiiso Light Railway (上磯軽便線) between Goryōkaku and Kamiiso (5.4 mi ≈ 8.8 km).
• 19222 September: the line is redesignated the Kamiiso Line (上磯線).
• 193025 October: the line is extended from Kamiiso to Kikonai (29.0 km).
• 193510 December: the line is extended from Kikonai to Yunotai (21.4 km).
• 193610 November: the final section from Yunotai to Esashi (20.7 km) opens, completing the Goryōkaku–Esashi through route; the whole line is simultaneously renamed the Esashi Line (江差線).
• 19871 April: with the division and privatisation of Japanese National Railways, JR Hokkaido succeeds to the whole Esashi Line as the first-class railway operator.
• 1988The Seikan Tunnel and the Kaikyō Line open, linking Hokkaidō and Honshū by rail; the Goryōkaku–Kikonai section of the Esashi Line lies on the approach and carries Tsugaru-Kaikyō-corridor limited expresses (Hakuchō, Super-Hakuchō) and the overnight Hamanasu.
• 201412 May: JR Hokkaido closes the Kikonai–Esashi section (42.1 km) to all traffic, ending rail service to Esashi.
• 201529 June: the Ministry of Land, Infrastructure, Transport and Tourism authorises South Hokkaido Railway's first-class railway operating licence for the Goryōkaku–Kikonai section (37.8 km), ahead of the 2016 transfer.
• 201622 March: the overhead wire in the Kikonai-station area is raised to 25 kV 50 Hz to match the voltage used where the route meets the Shinkansen and the Kaikyō Line.
• 201626 March: with the opening of the Hokkaido Shinkansen (Shin-Aomori–Shin-Hakodate-Hokuto), the Goryōkaku–Kikonai section (37.8 km) is transferred from JR Hokkaido to the new South Hokkaido Railway Company and renamed the Dōnan Isaribi Railway Line — the first third-sector conversion of a JR line in Hokkaidō since the Furusato Ginga Line closed in 2006.