Tōbu Koizumi Line

The line began as the Koizumi Line of the Chūgen Railway, which opened the section between Tatebayashi and Koizumimachi for service on 12 March 1917. The company was renamed the Jōshū Railway on 20 February 1922 and converted from a light railway into a local railway, before its railway business was acquired by Tobu Railway on 10 January 1937; with that purchase the Chūgen (Jōshū) Koizumi Line became the Tobu Koizumi Line. In its early years the railway added intermediate stops such as Narushima (1926) and several small halts along the original section.

From the late 1930s the line was reshaped by wartime industry. A freight-only branch, the Sengokugashi Line, opened from Koizumimachi to Sengokugashi on 13 April 1939, with Shin-Koizumi added as an intermediate station. On 1 June 1941 the section from Ōta to Koizumimachi opened to carry traffic to the Nakajima Aircraft Company's Koizumi plant, and a signal station, Koizumi Signal Station — the present Higashi-Koizumi — was set up; passenger service between that signal station and Ōta began the same day. Passenger operation between Koizumimachi and Nishi-Koizumi started on 10 July 1941, making Nishi-Koizumi the gateway station for the Nakajima works.

The network around Higashi-Koizumi was repeatedly rearranged during and just after the war. The small intermediate stations of Mejima, Mujinazuka and Kobukannon were closed on 25 December 1941. On 1 April 1942 the Koizumi Signal Station was upgraded to a passenger station and opened as Higashi-Koizumi, while passenger service at Koizumimachi was suspended; Ryūmai Station opened on 10 May 1942. Electrification followed in 1943, reaching Ōta–Nishi-Koizumi on 16 May and Tatebayashi–Higashi-Koizumi on 19 October. A military-backed plan to extend the Sengokugashi Line across the Tone River to Menuma, where it would have met the Kumagaya Line, was partly begun but abandoned when the Second World War ended; the licence finally lapsed in 1974.

In the post-war decades the line contracted again. Higashi-Koizumi reverted to a signal station on 20 September 1955 — usable only for transfers, not for boarding or alighting — and Koizumimachi's passenger service was restored, while Shin-Koizumi opened on the freight branch. Shin-Koizumi was closed in 1975, and on 1 October 1976 the Sengokugashi Line between Nishi-Koizumi and Sengokugashi was abandoned; its trackbed was later turned into the Izumi Greenway walking path. Higashi-Koizumi resumed passenger service on 1 April 1977 in step with the opening of a nearby high school, and the Koizumi Line settled into its present form as a local commuter route.

Freight, which had been central to the line's wartime purpose, ended on 1 October 1996, the last trains having run on 25 September. The remaining operations were progressively simplified for one-man working: the Higashi-Koizumi–Ōta branch went over to one-man operation on 19 March 2003, and through-running with the Kiryū Line — which had been suspended for elevation works at Ōta Station — resumed on 18 March 2006. One-man operation was then extended to the Tatebayashi–Nishi-Koizumi section on 28 September 2006, after which the entire Koizumi Line was operated one-man.

Today the Koizumi Line is worked entirely by one-man local trains, with services running between Tatebayashi and Nishi-Koizumi and, on the branch, through to and from the Kiryū Line via Ōta. Station numbering was introduced across all of its stations on 17 March 2012. Together with parts of the Isesaki, Sano and Kiryū lines it forms Tobu Railway's only loop circuit — Tatebayashi–Higashi-Koizumi–Ōta–Ashikagashi–Tatebayashi — over which ticket-holders may, within the loop, travel by either route without paying extra so long as they do not break their journey.

• 191712 March: the Chūgen Railway opens the Tatebayashi–Koizumimachi section, the origin of the Koizumi Line.
• 192220 February: the Chūgen Railway is renamed the Jōshū Railway; it converts from a light railway to a local railway.
• 192618 March: Narushima Station opens.
• 193710 January: Tobu Railway acquires the railway business of the Jōshū Railway; the line becomes the Tobu Koizumi Line.
• 193913 April: the freight-only Sengokugashi Line opens between Koizumimachi and Sengokugashi.
• 19411 June: Ōta–Koizumimachi opens to serve the Nakajima Aircraft Company's Koizumi plant, and Koizumi Signal Station (now Higashi-Koizumi) is set up; passenger service between Koizumimachi and Nishi-Koizumi follows on 10 July.
• 194125 December: the intermediate stations Mejima, Mujinazuka and Kobukannon are closed.
• 19421 April: Koizumi Signal Station is upgraded to a passenger station as Higashi-Koizumi, and passenger service at Koizumimachi is suspended; Ryūmai Station opens on 10 May.
• 1943The line is electrified: Ōta–Nishi-Koizumi on 16 May and Tatebayashi–Higashi-Koizumi on 19 October.
• 195520 September: Higashi-Koizumi reverts to a transfer-only signal station; passenger service at Koizumimachi resumes and Shin-Koizumi Station opens on the freight branch.
• 19761 October: the Sengokugashi Line between Nishi-Koizumi and Sengokugashi is abandoned; its trackbed later becomes the Izumi Greenway.
• 19771 April: Higashi-Koizumi resumes passenger service, timed to the opening of a nearby high school.
• 19961 October: freight services on the line end (the last trains ran on 25 September).
• 200319 March: one-man operation begins on the Higashi-Koizumi–Ōta branch.
• 200618 March: through-running with the Kiryū Line, suspended for elevation works at Ōta Station, resumes; on 28 September one-man operation begins on Tatebayashi–Nishi-Koizumi, making the whole line one-man.
• 201217 March: station numbering is introduced at all stations on the line.