In the planning stage of the Kosei Line, with the estimate that the track volume of the Tokaido Main Line would reach its limit, it was planned to construct a new line that would run from Yamashina Station to Nagao Station (Osaka Prefecture) on the Katamachi Line and to have freight trains enter a new Nagao yard and limited express trains enter Osaka Station from the Katamachi Line via the JR Tozai Line.
計画時は東海道本線の線路容量が限界になるであろうとの予測により、山科から片町線長尾駅(大阪府)に抜ける新線を作り、貨物列車を新設の長尾操車場に、特急列車を片町線からJR東西線経由で大阪に入れる構想であった。