Many Shinkansen lines were proposed during the boom of the early 1970s but have yet to be constructed. These are called Seibi Shinkansen or "planned Shinkansen." One of these lines, the Narita Shinkansen to Narita Airport, has been officially cancelled, but a few remain under development.



• Tōhoku Shinkansen extension from Hachinohe Station to Shin-Aomori is under construction and will open by 2010.
• Hokuriku Shinkansen extension to Kanazawa is under construction and will open by 2014. The complete extension of the line to Osaka is under development, and only Fukui Station is under construction.
• Kyūshū Shinkansen extension to Hakata is under construction and will open by 2010.
• The second Kyūshū Shinkansen route from Shin-Tosu to Nagasaki section is under development.
• The Hokkaidō Shinkansen from Shin-Aomori to Shin-Hakodate is under construction and will open by 2015. A further extension of the line from Shin-Hakodate to Sapporo is under development.