Seibu Tamagawa Line

The line owes its existence to river gravel. It was built by the Tama Railway (Tama Tetsudo), a company established in August 1910 to carry gravel dug from the bed of the Tama River. A provisional licence for a line between Sakai and Koremasa had been granted in February 1908, and the route was designated a light railway in November 1910. The project drew an objection from the Tokyo Astronomical Observatory, which was planning to move to Mitaka and feared that a steam railway running nearby would interfere with its observations; the dispute was apparently resolved in the railway's favour, as the line was not significantly diverted. The company also secured rights to extract gravel at Tama for some two decades — gravel extraction from the Tama River was eventually banned in 1964.

The first section, between Sakai Station (today's Musashi-Sakai) and Kita-Tama Station (today's Shiraitodai), opened on 22 October 1917, with intermediate Shin-Koganei Station; Sakai, Shin-Koganei and Kita-Tama opened that day. On 1 June 1919 the line was extended from Kita-Tama to Tsunehisa Station (today's Kyoteijo-mae), at first for freight only, and on 1 July 1919 Sakai Station was renamed Musashi-Sakai. The final segment, from Tsunehisa to Koremasa, opened on 20 June 1922, completing the 8.0-kilometre route and opening Koremasa Station. In these early years the railway was overwhelmingly a freight operation, carrying far more gravel by weight than it did passengers.

On 31 August 1927 the Tama Railway was absorbed by the (old) Seibu Railway, which renamed it the Tama Line; the transfer had been approved in the Official Gazette earlier that month. Passenger traffic, until then almost an afterthought to the gravel business, began to grow: in 1929 the company introduced gasoline railcars and opened Tama-bochi-mae Station (today's Tama) near the increasingly popular Tama Cemetery, after which trains ran as often as every fifteen minutes between Musashi-Sakai and Tama-bochi-mae on Sundays, holidays and during the equinox visiting seasons. The (old) Seibu Railway was a forerunner of today's Seibu Shinjuku Line group; it was merged into the Musashino Railway in 1945 to form Seibu Agricultural Railway, which became the present-day Seibu Railway in 1946.

During the Pacific War the line gained an industrial role, with a spur serving a Nakajima Aircraft factory and freight running to works along the route. After the war the whole line was electrified in 1950, the Musashi-Sakai–Kita-Tama section being energised on 11 July and the Kita-Tama–Koremasa section on 1 November. Freight services ceased in 1967, leaving the line a purely passenger railway. Its name changed several times: after being the Tama Line under Seibu, it became the Musashisakai Line in 1952 before finally being renamed the Tamagawa Line in 1955, the name it still carries.

The line's isolation from the rest of the Seibu system is a direct legacy of its origins as the independent Tama Railway absorbed in 1927, and it has remained a self-contained branch ever since. Its name also led to a later naming convention elsewhere: when Tokyu split its Mekama Line in August 2000 into the Meguro Line and a new Tamagawa Line, the latter was officially styled the Tokyu Tamagawa Line precisely because Seibu was already using the name 'Tamagawa Line'. Meanwhile the redevelopment of the former 'Kanto-mura' site — land around the wartime Chofu airfield that had been requisitioned by occupation forces and returned in 1974 — reshaped the line's catchment: the Tokyo University of Foreign Studies moved there in 2000 and the National Police Academy and Metropolitan Police Academy in 2001, substantially increasing the line's ridership.

In the modern era the Tamagawa Line has been steadily modernised. One-man operation, trialled from 1995, was fully adopted on 1 April 1996, and PASMO smart-card ticketing was introduced in 2007. In 2001 Tama-bochi-mae and Kita-Tama stations were renamed Tama and Shiraitodai, and between 2003 and 2009 Musashi-Sakai Station was rebuilt on an elevated structure. The line's rolling stock was renewed in 2010, when the older 101 series — by then the last of its kind on the Seibu network — was replaced by New 101 series trains, which the line still uses; because the depot at Shiraitodai is small, these cars are periodically exchanged with the rest of the Seibu fleet via occasional dedicated transport over the JR connection. The line marked its 100th anniversary in 2017, and from 2023 it served as Seibu's testbed for a wireless train-control (CBTC) system.

• 19086 February: a provisional railway licence is granted for a line between Sakai and Koremasa (Tama-mura).
• 1910August: the Tama Railway is established to haul gravel from the Tama River; in November the line is designated a light railway.
• 191722 October: the Tama Railway opens its first section, Sakai (now Musashi-Sakai) to Kita-Tama (now Shiraitodai), with Shin-Koganei Station.
• 19191 June: the line is extended from Kita-Tama to Tsunehisa (now Kyoteijo-mae), at first for freight only; on 1 July Sakai Station is renamed Musashi-Sakai.
• 192220 June: the final section from Tsunehisa to Koremasa opens, completing the 8.0 km line; Koremasa Station opens.
• 192731 August: the Tama Railway is absorbed by the (old) Seibu Railway and renamed the Tama Line (transfer approved in the Official Gazette on 3 August).
• 1929Gasoline railcars are introduced; Tama-bochi-mae Station (now Tama) opens near Tama Cemetery, after which frequent cemetery-visitor trains run from Musashi-Sakai.
• 1950The whole line is electrified: Musashi-Sakai–Kita-Tama on 11 July and Kita-Tama–Koremasa on 1 November.
• 195225 March: the line is renamed the Musashisakai Line.
• 19541 May: Tsunehisa Station is renamed Kyoteijo-mae.
• 19559 May: the line is renamed the Tamagawa Line, the name it still carries.
• 1967Freight services cease, leaving the line a purely passenger railway.
• 19961 April: after a trial from 1995, the line moves fully to one-man operation.
• 2000When Tokyu splits its Mekama Line into the Meguro Line and a new Tamagawa Line, the latter is named the 'Tokyu Tamagawa Line' because Seibu already used the name 'Tamagawa Line'.
• 200128 March: Tama-bochi-mae and Kita-Tama stations are renamed Tama and Shiraitodai.
• 200718 March: PASMO smart-card ticketing is introduced across the line.
• 2010March–November: the older 101 series, by then the last on the Seibu network, is replaced by New 101 series trains; the old 101 series makes its final run on 9 November.
• 201729 September: the line marks its 100th anniversary with commemorative events.
• 2023The line becomes Seibu's testbed for a wireless train-control (CBTC) system, with running tests following in 2024.