The project for the Tozai Line started in or around 1965 as a means of public transportation that would connect the eastern region of Kyoto City (Yamashina Ward and eastern Fushimi Ward)--where the construction of surrounding roads along the Tozai Line couldn't keep up with the rapid population growth in those areas, resulting in serious traffic jams--with the large cities, and was officially carried at a city council meeting held in 1969.
東西線沿線は人口の伸びが著しい傾向を見せるが、それに周辺の道路整備が追い付かずに渋滞が深刻化していた京都市東部地域（山科区・伏見区東部）と都心部をつなぐための交通機関として1965年頃から計画が進められ、1969年の市議会で建設が正式に決定。