The Yamanote line service - the famous loop line in Tōkyō - has its own double track all around the loop. But, officially it belongs to three different lines:

Tōkaidō Hon line	Tōkyō - Shinagawa
Yamanote line	Shinagawa - Tabata
Tōhoku Hon line	Tabata - Tōkyō

Along the official Yamanote line runs also a double track called Yamanote Freight Line. It is not used by so many freight trains today, but by other passenger services not stopping at all stations:
Saikyō line between Ōsaki and Ōmiya uses the freight line between Ōsaki and Ikebukuro.
Shōnan-Shinjuku line between Ōfuna and Ōmiya uses the freight line between Ōsaki and Komagome where the freight line tracks (and Shōnan-Shinjuku line) bypasses Tabata station and joins the Tōhoku Hon line north of Tabata station.
The freight line tracks are also used by some other services, e.g Narita Express trains.

Trains running clockwise; Tōkyō - Shinagawa - Shinjuku - Tabata - Tōkyō; are called soto-mawari "outer circle".
Trains running counter-clockwise are called uchi-mawari "inner circle".

The traffic pattern below is for the outer cirle trains. From a train number point of view, a loop train starts and ends in Ōsaki.