It happened to coincide with the time when Prime Minister Kakuei TANAKA proposed 'Nippon Retto Kaizo-Ron' (Building a New Japan) for promoting the development of land in Japan, and it seemed that the construction of these Shinkansen lines could progress smoothly.
折しも田中角栄内閣総理大臣によって、国土開発を促進する「日本列島改造論」が提唱され、整備は順調に進むかに見えた。