The Keio New Line shares the same platforms with the Toei Shinjuku Line at Shinjuku Station. From here trains travel west-southwest. At Hatsudai Station, the westbound platform is two floors underground while the eastbound one is three floors underground. (Both platforms are on the north side of the station.) At Hatagaya Station both platforms are two floors underground with platforms on either side of the two central tracks. From this station, the Keio New line diverges from the Kōshū Kaidō and heads towards the Keio Line further south. The Keiō Line parallels the outside of the New Line on an elevated viaduct over Prefectural Route 420 (Nakano Dori) until Sasazuka Station.