In 1957, 'the trunk railway investigation committee' within JNR submitted a report insisting that the transportation power of the Tokaido main line would be saturated sooner or later and laying railways other than the existing ones would be required.
1957年、国鉄内部の「幹線調査会」は、東海道本線の輸送力飽和は早晩必至とし、現在線以外の線路増設が必要であると答申した。