On October 1, 1964, the first Shinkansen left Tokyo for Shin-Osaka, covering the 515 kilometres of the Tokaido corridor in four hours against the six and a half the old narrow-gauge line needed. The opening was timed nine days ahead of the Tokyo Olympics. Maximum speed was 210 km/h. The trains ran on dedicated standard-gauge track with no level crossings and no curve sharp enough to require slowing.
The old line was full. The Tokaido corridor carried about half of Japan's rail passengers and much of its freight on a single pair of tracks, and Japanese National Railways had been told in the 1950s that doubling it would not be enough. The engineer put in charge, Hideo Shima, had been head of rolling stock design during the war and had carried the blame for a fire at Sakuragicho station in 1951 that killed 106 people. He came back to run the project and was told to finish in five years. The budget was about 380 billion yen, roughly a billion dollars, and it overran badly.
What made the line possible was that it was new from end to end. Standard gauge rather than the 1,067 mm Cape gauge the rest of Japan ran on, continuously welded rail, automatic train control in the cab, and signalling designed to stop a train without the driver doing anything. There were no level crossings. The whole corridor was grade separated, which is the expensive part and the reason the system works.
It was not the first fast train, since several European services ran at comparable speeds. What was new was building a separate railway for high speed only, on a corridor that already carried heavy traffic, and running it at that frequency, six-minute headways at peak, with punctuality measured in seconds. The first year carried 11 million passengers. The network carried about 160 million a year by 2023.
The Shinkansen has had no passenger death from a train accident in six decades, which is the number the system is judged by. It is also the reason the bullet train became the standard answer to what to do about a busy intercity corridor, and why the French TGV, the German ICE and the high-speed lines built in China from 2008 follow the same principle: dedicated track, no crossings, and nothing shared with the slow network.