Sendai Subway Tōzai Line

Sendai's first subway, the Namboku Line, opened in 1987, and planning for a second, cross-town route to complement it followed. The Tōzai Line was conceived as part of the regional Sendai–Shiogama urban plan as Urban Rapid Railway No. 4, formally the Sendai City Rapid Railway Tōzai Line. On 23 March 2000 the mayor of Sendai announced the chosen route and the decision to adopt linear-motor rolling stock, fixing the basic form of the project. A dedicated Tōzai Line Construction Headquarters was established on 1 April 2003 to carry the work forward.

The licensing and approval steps came in quick succession. The Transportation Bureau applied to the national transport ministry for a Type 1 railway business licence in June 2003 and received it on 18 September 2003; approval to begin construction work followed in August 2005. Main civil-engineering work began on 1 November 2006, and a groundbreaking and safety ceremony was held at the Rokuchōme Station site on 5 February 2007. Because the line was designed as a compact linear-motor subway, its tunnels have a cross-section only about two-thirds that of the Namboku Line, with five curves as sharp as 105-metre radius and a gradient as steep as 57 per mil — figures well beyond the limits of a conventional subway.

Tunnelling progressed through the hills west of the centre, and a breakthrough ceremony for the Aobayama Tunnel was held on 26 October 2009. The project was then struck by the Great East Japan Earthquake of 11 March 2011, which caused material damage and forced the suspension of work across every section of the line. Construction resumed in stages from 20 June 2011, and all sections were back in operation by 1 September 2011, allowing the schedule to be largely recovered.

With the structures complete, the line moved into fitting-out and testing. Track-laying began in February 2012, the station and vehicle designs were unveiled over 2012, and the first 2000-series train set was delivered to the Arai depot on 29 September 2014. Test running over the full line was achieved for the first time on 3 March 2015, and after final inspection by the Tōhoku District Transport Bureau in November 2015 the line was cleared for service.

The Tōzai Line opened to passengers on 6 December 2015, with a departure ceremony for the first train at Arai Station, giving Sendai its second subway route after twenty-eight years. The Construction Headquarters was disbanded on 31 March 2016, its task complete. In 2017 the line was recognised with a Prime Minister's commendation for its barrier-free and universal design, reflecting the accessibility built into its thirteen stations.

Since opening, the Tōzai Line has settled into the role of an east–west cross-town spine complementing the Namboku Line, with Sendai Station as the pivotal interchange between the two and with the JR network. A timetable revision on 1 July 2023 lengthened daytime headways from roughly seven-to-eight minutes to eight-to-ten minutes and extended station dwell times at most intermediate stops, adjusting the service to observed demand while keeping the compact linear-motor system at the heart of Sendai's urban rail.

• 200023 March: the mayor of Sendai announces the chosen Tōzai Line route and the decision to adopt linear-motor rolling stock.
• 20031 April: the Tōzai Line Construction Headquarters is established; on 18 September the Type 1 railway business licence is granted.
• 200510 August: approval to begin construction work is granted by the transport minister.
• 20061 November: main civil-engineering construction work begins.
• 20075 February: a groundbreaking and safety ceremony is held at the Rokuchōme Station site.
• 200926 October: a breakthrough ceremony is held for the Aobayama Tunnel.
• 201111 March: the Great East Japan Earthquake causes damage and suspends work on all sections; construction resumes in stages from 20 June and all sections are back in operation by 1 September.
• 2012February: track-laying work begins; the station and vehicle designs are unveiled over the course of the year.
• 201429 September: the first 2000-series train set is delivered to the Arai depot.
• 20153 March: a train runs the full line for the first time in testing; 10 November: the line passes final inspection by the Tōhoku District Transport Bureau; 6 December: the line opens to passengers, with a departure ceremony for the first train at Arai Station.
• 201631 March: the Tōzai Line Construction Headquarters is disbanded, its task complete.
• 201721 December: the line receives a Prime Minister's commendation for its barrier-free and universal-design measures.
• 201916 March: train departure times are added to the station guidance displays.
• 20231 July: a timetable revision lengthens daytime headways from about 7–8 minutes to 8–10 minutes and extends station dwell times at most intermediate stations.