Kyoto Municipal Subway Tōzai Line

The line grew out of post-war proposals by the Kyoto Municipal Transportation Bureau, which had considered a new municipal streetcar — and at one point an elevated railway — linking Rokujizō, Daigo and Keage before running along the centre of Oike-dōri. As automobile use grew, that idea stalled and was reworked as a subway. With the population along the east–west corridor rising faster than the local roads could absorb, a plan to connect the eastern part of the city with the centre was developed from 1965 and formally approved by the city in 1969; construction of the Daigo–Nijō section was set to begin in 1975.

A complication lay along the planned route: the Keihan Keishin Line already ran above ground between Misasagi and Sanjō-Keihan, raising the prospect of direct competition. Kyoto City and the Keihan Electric Railway resolved it by founding a third-sector company, Kyoto Rapid Railway (京都高速鉄道株式会社), which took a Type-3 railway-business licence to own the tracks of that section while the city took a Type-2 licence to run the trains over them. Construction beneath the historic city was repeatedly interrupted by the discovery of buried ruins and faced difficult tunnelling under the Kamo River and the Tōkaidō Shinkansen.

The groundbreaking ceremony was held on 8 November 1989. The first section, between Daigo and Nijō, opened on 12 October 1997, and on the same day the Keihan Keishin Line began through services onto the new subway, running from Hamaōtsu (today Biwako-hamaotsu) via Misasagi as far as Kyoto Shiyakusho-mae. When the above-ground Keishin section was removed, its Kujōyama and Hinooka stations — which had no subway counterparts — were abolished; residents near Kujōyama asked for a subway station there, but difficult local topography and low projected ridership left the request unfulfilled.

The line was then extended at both ends. On 26 November 2004 the southeastern section from Daigo to Rokujizō opened, giving the line its present eastern terminus and a connection to the JR Nara Line and the Keihan Uji Line at Rokujizō. On 16 January 2008 a westward extension from Nijō to Uzumasa Tenjingawa came into service, and Keihan Keishin Line through trains, which had previously turned back short of the western end to keep operating costs balanced, were extended all the way to the new terminus.

With the network complete, the third-sector arrangement was wound up: the Kyoto Municipal Transportation Bureau dissolved Kyoto Rapid Railway, and from 1 April 2009 the company's Sanjō-Keihan–Misasagi section was transferred to the city, making the bureau the sole Type-1 operator over the entire line. Later operational milestones included the start of nationwide IC-card interoperability on 23 March 2013 and, from 2 October 2015, a late-night "Kotokin Liner" extra service, which was suspended in March 2021.

Today the Tōzai Line carries on the order of 170,000 passengers a day, well below the figure once projected for it, a shortfall noted in Japanese sources. Its stations are designed for step-free access, with island platforms, platform screen doors and per-station colour coding throughout. A long-discussed westward extension toward the Rakusai district of Nishikyō-ku, and possibly on to Nagaokakyō, remains only a proposal; for the present the line ends at Uzumasa Tenjingawa, where it meets the Keishin Line through service and the Randen Arashiyama Main Line nearby.

• 1969Kyoto City formally approves a plan, developed from 1965, for an east–west transport link connecting the eastern part of the city with the centre.
• 19898 November: the groundbreaking ceremony for the line is held.
• 199712 October: the first section, Daigo–Nijō, opens; the Keihan Keishin Line begins through services from Hamaōtsu via Misasagi to Kyoto Shiyakusho-mae.
• 200015 March: daytime full-length service is increased from six to eight trains per hour.
• 200426 November: the southeastern section from Daigo to Rokujizō opens, giving the line its present eastern terminus.
• 200816 January: the westward extension from Nijō to Uzumasa Tenjingawa opens; Keihan Keishin Line through trains are extended to the new terminus.
• 20091 April: Kyoto Rapid Railway transfers the Sanjō-Keihan–Misasagi facilities to the city, which becomes the sole Type-1 operator over the whole line.
• 201019 March: a wholesale timetable revision is carried out.
• 201323 March: nationwide mutual use of transit IC cards begins on the line.
• 20152 October: the late-night 'Kotokin Liner' extension service begins operation (suspended from March 2021).