Haijima Line

The Haijima Line took its present form comparatively recently, in 1968, and is unusual in that it was assembled by linking together several short railways of quite different origins and then completing the route with a final new section. Because of this piecemeal construction the line's distance posts are split into four separate sequences rather than running continuously from one end to the other. The three original components — a sightseeing branch toward the Murayama reservoir, a line built over a wartime factory siding, and a section grown out of an aircraft-plant railway — were joined in stages before the through line opened.

The oldest part is the Kodaira–Hagiyama section. It was opened in 1928 by the Tamako Railway (多摩湖鉄道) as a short branch, the Kodaira Line, between Hagiyama and Moto-Kodaira (near present-day Kodaira), built to connect with the lines of the old Seibu Railway. The segment was electrified at 600 V DC in 1932. In 1940 the Tamako Railway was absorbed by the Musashino Railway, the corporate forerunner of today's Seibu Railway, and in 1958 Hagiyama Station was relocated to serve sightseeing traffic to the Murayama reservoir, after which through running began between Kodaira, Hagiyama and the Tamako (Lake Tama) terminus.

The Ogawa–Tamagawa-Jōsui section had a separate origin as an industrial railway. It had been laid as a dedicated siding serving the Hitachi Aircraft Tachikawa plant in the former village of Yamato (now the city of Higashiyamato) in Kita-Tama District. After the Second World War Seibu Railway acquired the line and opened it, in 1950, as the Jōsui Line (上水線) between Ogawa and Tamagawa-Jōsui, a 4.6 km route that at first was non-electrified and worked by diesel railcars. It was electrified at 1,500 V DC in 1954, and for some years it remained a minor branch.

The pieces were brought together in the 1960s. In 1962 a new 1.6 km section opened between Hagiyama and Ogawa — partly rebuilt from a factory siding that had served the Bridgestone Tire Tokyo plant, itself successor to an army installation reached by a siding laid in 1944 — and the Kodaira–Hagiyama segment was incorporated into the Jōsui Line; through service to the Shinjuku Line then began. After the Kodaira–Hagiyama stretch was double-tracked in 1967, the final 7.1 km from Tamagawa-Jōsui to Haijima opened on 15 May 1968, completing the through route, and the whole Kodaira–Haijima line was renamed the Haijima Line. Because the extension involved relaying the tracks within Tamagawa-Jōsui Station, a fresh set of distance posts begins there.

Over the following decades the line was steadily upgraded and its stations expanded. Omebashi Station was renamed Higashi-Yamatoshi in 1979 and elevated in 1980, and Musashi-Sunagawa Station opened in 1983. Double-tracking proceeded section by section between 1979 and 1991 — Hagiyama–Ogawa in 1979, Musashi-Sunagawa–Seibu-Tachikawa in 1983, Nishi-Ogawa–Higashi-Yamatoshi in 1987, Higashi-Yamatoshi–Tamagawa-Jōsui in 1988 and Ogawa–Nishi-Ogawa in 1991 — although stretches between Tamagawa-Jōsui and Musashi-Sunagawa and between Seibu-Tachikawa and Haijima remain single track. The Nishi-Ogawa passing loop, on the single-track section, was abolished in 1991, and trains were lengthened to eight cars in 1988 and ten cars in 1997.

The Haijima Line provides through service all day toward Tanashi and Seibu-Shinjuku on the Shinjuku Line, supplemented by shuttle workings based on Tamagawa-Jōsui Station, where a depot is located. A limited-stop Haijima Rapid service — the line's first service to skip stations — ran from 2008 until 2012, when it was abolished and replaced by Express trains. The most prominent service today is the Haijima Liner, an all-reserved-seat express introduced on 10 March 2018 using Seibu 40000 series trainsets; it links Haijima with Seibu-Shinjuku and requires a reserved-seat ticket in addition to the ordinary fare. The line interchanges with the Tama Toshi Monorail at Tamagawa-Jōsui and with the JR Ōme, Itsukaichi and Hachikō lines at its Haijima terminus.

• 19282 November: the Tamako Railway opens its Kodaira Line, Hagiyama–Moto-Kodaira (1.0 km) — the oldest part of the present route.
• 193215 August: the Hagiyama–Moto-Kodaira section is electrified at 600 V DC.
• 194012 March: the Tamako Railway is merged into the Musashino Railway, the forerunner of today's Seibu Railway.
• 194915 November: Moto-Kodaira Station is merged into Kodaira Station.
• 195015 May: the Jōsui Line opens, Ogawa–Tamagawa-Jōsui (4.6 km), non-electrified — converted from a dedicated siding (originally serving the Hitachi Aircraft Tachikawa plant) acquired by Seibu in 1949.
• 195412 October: the Ogawa–Tamagawa-Jōsui section is electrified at 1,500 V DC; on 18 March 1955 the Kodaira–Hagiyama section is raised to 1,500 V DC.
• 19621 September: Hagiyama–Ogawa (1.6 km) opens, partly rebuilt from a Bridgestone Tire factory siding; the Kodaira–Hagiyama segment is incorporated into the Jōsui Line and through service to the Shinjuku Line begins.
• 19677 November: the Kodaira–Hagiyama section is double-tracked.
• 196815 May: Tamagawa-Jōsui–Haijima (7.1 km) opens, completing the through route; Seibu-Tachikawa Station opens and the Kodaira–Haijima line is renamed the Haijima Line.
• 197925 March: Omebashi Station is renamed Higashi-Yamatoshi Station; on 7 December the Hagiyama–Ogawa section is double-tracked.
• 1983Musashi-Sunagawa Station opens (12 December) and the Musashi-Sunagawa–Seibu-Tachikawa section is double-tracked (1 December).
• 19882 November: the Higashi-Yamatoshi–Tamagawa-Jōsui section is double-tracked (the Nishi-Ogawa SB–Higashi-Yamatoshi section having been double-tracked on 5 March 1987); on 5 December trains are lengthened to eight cars.
• 199129 March: the Ogawa–Nishi-Ogawa section is double-tracked and the Nishi-Ogawa passing loop / signal box is abolished; trains are later lengthened to ten cars on 12 March 1997.
• 200814 June: the Haijima Rapid service begins — the line's first limited-stop service.
• 201230 June: the Haijima Rapid service is abolished and replaced by Express trains.
• 201810 March: the all-reserved-seat Haijima Liner begins, using Seibu 40000 series trainsets between Haijima and Seibu-Shinjuku.