The Yokosuka-Sobu Rapid Line (横須賀・総武快速線) is a service run by East Japan Railway Company (JR East). It runs from Kurihama Station in Yokosuka, Kanagawa, through Tokyo Station, to Chiba Station in Chiba city.
History
In the high-growth years, the Tokaido Main Line (東海道本線) between Tokyo and Ofuna was crowded at rush hour. Shonan trains (湘南電車) and Yokosuka Line (横須賀線) trains shared the same tracks there. More trains were added again and again until the line reached its limit. The Sobu Main Line (総武本線) was also badly crowded at rush hour. In 1965 Japanese National Railways (JNR) started a new long-term plan. Its commuter plan for five directions around Tokyo included a four-track line on the Sobu Main Line between Tokyo and Tsudanuma, and a link between the Yokosuka Line and the Sobu Main Line through underground platforms at Tokyo.
Work on a new underground tunnel between Tokyo and Ryogoku began in April 1965. Most of it was built by shield tunnelling, and it was the first urban tunnel built by JNR. Signals could not be seen far enough inside the tunnel, so it used automatic train control (ATC), the first system of its kind on JNR conventional lines. The Sobu Rapid Line opened on 15 July 1972, and the Sobu Main Line's starting point moved from Ochanomizu to Tokyo. The new Tokyo underground station opened the same year. Crowding on the escalators and central passage at Tokyo led to an emergency measure: the Rapid was extended to Shinagawa on 1 October 1976.
A second underground line, between Tokyo and Shinagawa, was started in March 1968 and completed on 28 June 1973. JNR planned new freight lines so that the Yokosuka Line could be separated from the Shonan trains. Local residents opposed the new freight line, and the work was delayed. In June 1978 the Kanagawa land commission ruled that land for one section could be taken under the Land Expropriation Act. The new freight line opened on 1 October 1979. On 1 October 1980 the Yokosuka Line and the Shonan trains were separated onto their own tracks between Tokyo and Ofuna, and direct running between the Yokosuka Line and the Sobu Rapid Line began. The separation was called 'SM separation', after the S trains (Yokosuka) and M trains (Shonan).
The quadruple track between Tsudanuma and Chiba was completed in July 1981. From 23 July 1984 the Home Liner Tsudanuma (ホームライナー津田沼) ran between Tokyo and Tsudanuma. Nishi-Oi station opened on 2 April 1986. On 1 April 1987 JNR was split up and privatised, and the line passed to JR East.
New Tokyo International Airport (now Narita International Airport) opened on 20 May 1978. Some Rapid trains were extended to Narita station from 1 March 1978. On 19 March 1991 the airport branch of the Narita Line (成田線) opened from Narita station to Narita Airport station, and Narita Express trains began running. From 1 May 1991 the Rapid trains to Narita Airport were given the nickname 'Airport Narita' (エアポート成田).
E217 series stainless-steel trains began service on 3 December 1994. In December 1999 the 113 series trains were replaced by E217 series trains, and the top speed rose from 100 km/h to 120 km/h. The fastest trip between Tokyo and Chiba then took 38 minutes. On 1 December 2001 the Shonan-Shinjuku Line (湘南新宿ライン) began. In the daytime, some Yokosuka Line trains ran between Shinjuku and Zushi and Yokosuka. That service stopped on 16 October 2004.
Musashi-Kosugi station opened on 13 March 2010. On 12 October 2019, Typhoon No. 19 (台風19号) brought heavy rain, and the Yokosuka Line area inside Musashi-Kosugi station was flooded. In September 2018 JR East announced E235 series trains to replace the E217 series. The E235 1000 series entered service on 21 December 2020. On 12 March 2022 the commuter rapid service was discontinued. In June 2026 the Yokosuka Line between Tokyo and Shinagawa was closed all day from 5 to 7 June for tunnel repairs, and more full-day closures were planned for 4 to 6 September and 6 to 8 November 2026. On 1 July 2026 JR East replaced its branch offices with business divisions, and the line was placed under several of them.
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Written by an AI from the line's history on Japanese Wikipedia, nothing else, and checked by a program for dates and numbers that are not in those facts. It can still be wrong. Adapted from Japanese Wikipedia, CC BY-SA 4.0; this text is shared under the same licence.