Kyoto Dento opened the Eizan-heitan Line (currently the Eizan Main Line of Eizan Electric Railway Co., Ltd.) in 1925; however, it took a lot of time to start the construction because it was impossible to lay the Oto Line on the ground, owing to the fact that the line would inevitably intersect with the Kyoto City Trams at grade and might also detract from the surroundings, and because of the financial conditions of Keifuku Electric Railroad the company wasn't capable of constructing a subway line.
京都電燈は1925年に叡山平坦線（現在の叡山電鉄叡山本線）を開業させたが、鴨東線については京都市電と平面交差することになることや景観の問題から地上に作ることができず、また、京福電鉄の経済的な事情から地下鉄として建設することもできず、なかなか着工されなかった。