Read more about the line in English Wikipedia: Shōnan–Shinjuku Line

The Shōnan-Shinjuku Line is the name of a train service serving the route Ōfuna - Yokohama - Ōsaki - Shibuya - Shinjuku - Ikebukuro - Akabane - Ōmiya. The traffic started in December 2001 and has been continously extended.
The line is not an official railway line - it runs along other lines, but in two places it makes short cuts using freight tracks that are not considered offical lines.

At the *-marked sections. the tracks are used only by Shōnan-Shinjuku Line. At the other sections, the tracks are shared with other lines.

Between Ikebukuro and Akabane, the line runs along Yamanote Line to Komagome, bypassing Tabata north of the station and then along the Utsunomiya Line tracks.

There are no passenger platforms at Tsurumi station for the Yokosuka Line tracks.

The distances Nishi-Ōi - Ōsaki and Ikebukuro - Akabane are not official distances.