In the era of Japan National Railways, there were plans to operate trains through both Shinkansen lines (experimental 961-type Shinkansen train-cars were manufactured for testing the through operations, and platforms 14 and 15 for the Tokaido Shinkansen in Tokyo Station are curved towards the Tohoku Shinkansen line side, because they were made assuming that trains were to be operated through both Shinkansen lines).
国鉄時代には、当初両線の直通運転を前提として建設の計画がなされていた（直通運転の実験用に試験車両新幹線961形電車が製造された、また、東京駅の東海道新幹線14・15番ホームは直通を想定して作られたため、ホームが東北新幹線側にカーブしている）。