Which Shinkansen line’s extension from Okayama to Hakata opened in 1975?

The Sanyo Shinkansen’s extension from Okayama to Hakata opened in 1975.

The Sanyo Shinkansen runs westward from Shin-Osaka through the cities of western Honshu to Hakata Station in Fukuoka, on Kyushu. Its first section, between Shin-Osaka and Okayama, began service in 1972; the 1975 extension completed the route to Hakata.

This opening created a continuous high-speed rail link between Tokyo and northern Kyushu, using the Tokaido Shinkansen east of Shin-Osaka and the Sanyo Shinkansen west of it. Through services later made long-distance journeys between Tokyo and Hakata possible without changing trains.

The line is sometimes confused with the Kyushu Shinkansen. The Sanyo Shinkansen ends at Hakata, while the Kyushu Shinkansen continues south from Hakata toward Kagoshima-Chuo. Hakata is therefore an important interchange between the two lines.