Keisei Main Line

The line opened on 3 November 1912, when the section from Magarikane (now Keisei Takasago) to Iyoda (now Edogawa) entered service built to 1,372 mm gauge. According to the Japanese-language history, the line's starting point at opening was not Keisei Ueno but Oshiage, on what is today the Oshiage Line; the western origin was later shifted toward the present Keisei Ueno after Keisei acquired a licence held by the Tsukuba Kōsoku Electric Railway, taking effect when Nippori Station opened. The line was progressively extended in both directions: it reached the Narita area on 25 April 1930 (Narita-Hanasakichō to Narita, now Keisei Narita), the Nippori–Aoto section opened on 19 December 1931, and the final inland link from Ueno-kōen (now Keisei Ueno) to Nippori opened on 10 December 1933. In 1944 the Ueno-kōen to Keisei Narita route was designated the Main Line, while the Oshiage to Aoto section became the Oshiage Line. On 20 February 1945 the entire line was converted from a tramway under the Tramway Act to a railway under the Local Railway Act.

The most consequential later engineering change was a change of track gauge. All sections had opened as electrified dual track unless noted otherwise, and the line was regauged from its original 1,372 mm to the 1,435 mm standard gauge in 1959. The Japanese chronology dates the conversion in stages, from the Sōgosandō–Keisei Narita section on 14 October 1959 through to the Keisei Ueno–Nippori section on 30 November 1959, at which point standard-gauging was complete. Today the line is electrified at 1,500 V DC using overhead catenary, with a maximum speed of 110 km/h and C-ATS train protection. Its track configuration is quadruple-track between Aoto and Keisei Takasago, double-track on the Keisei Ueno–Aoto and Keisei Takasago–Narita Airport Terminal 2·3 sections, and single-track between Narita Airport Terminal 2·3 and Narita Airport. Ownership is split: Keisei Electric Railway owns the line from Keisei Ueno to the Komaino signal box, and Narita Airport Rapid Railway owns the section from Komaino to Narita Airport.

Airport access defines the line's modern role. Skyliner service began on 30 December 1973. On 21 May 1978, timed to the opening of the New Tokyo International Airport (Narita), the section from Keisei Narita to Narita Airport — the station now called Higashi-Narita — opened; that branch is today the Higashi-Narita Line. On 19 March 1991 the section from the Komaino junction to the present Narita Airport station opened, with its facilities owned by Narita Airport Rapid Railway, and on 3 December 1992 Narita Airport Terminal 2·3 station (Kūkō Daini Biru) opened. In 2010 the Narita Sky Access opened as a bypass of the line, reducing the role of the main line in airport access; following the 17 July 2010 timetable revision tied to the opening of the Narita Sky Access Line, most Skyliner trains and most Haneda-airport through services were rerouted via that line. The Skyliner connects Keisei Ueno and Narita Airport Terminal 1, running on the Main Line between Keisei Ueno and Keisei Takasago and on the Narita Sky Access Line beyond, and covers the entire route in 44 minutes (36 minutes from Nippori to Narita Airport Terminal 2·3).

The line is operated by Keisei Electric Railway, with depots at Takasago and Sōgo (the infobox names Sogosando). Beyond the reserved-seat Skyliner, services include the seasonal Cityliner, the morning-only Morningliner and evening-only Eveningliner, and a range of non-charged train types — Limited Express, Access Express, Commuter Express, Rapid and Local — many of which run through to the Oshiage Line and onward via the Toei Asakusa Line and Keikyū network toward Haneda Airport and Yokohama. The English infobox records a daily ridership of 500,121 in fiscal year 2010.

• 19123 November: the line opens between Magarikane (now Keisei Takasago) and Iyoda (now Edogawa), built to 1,372 mm gauge.
• 193025 April: the line reaches the Narita area as the Narita-Hanasakichō to Narita (now Keisei Narita) section opens.
• 193119 December: the Nippori to Aoto section opens.
• 193310 December: the Ueno-kōen (now Keisei Ueno) to Nippori section opens, completing the route to Ueno.
• 1944The Ueno-kōen to Keisei Narita route is designated the Main Line; the Oshiage to Aoto section becomes the Oshiage Line.
• 194520 February: the entire line is converted from a tramway under the Tramway Act to a railway under the Local Railway Act.
• 1959The line is regauged from 1,372 mm to 1,435 mm standard gauge in stages, from the Sōgosandō–Keisei Narita section on 14 October to the Keisei Ueno–Nippori section on 30 November, when standard-gauging is completed.
• 197330 December: Skyliner service begins.
• 197821 May: timed to the opening of the New Tokyo International Airport (Narita), the Keisei Narita to Narita Airport (now Higashi-Narita) section opens, today the Higashi-Narita Line.
• 199119 March: the Komaino junction to the present Narita Airport station section opens, with facilities owned by Narita Airport Rapid Railway.
• 19923 December: Narita Airport Terminal 2·3 station (Kūkō Daini Biru) opens.
• 2010The Narita Sky Access opens as a bypass of the line; a 17 July timetable revision reroutes most Skyliner and Haneda through services via the Narita Sky Access Line, reducing the main line's role in airport access.