Overview
The line was built with a track gauge of 1,372 mm (4 ft 6 in) to allow through operations onto the Keiō network. The line was planned as Line 10 according to reports of a committee of the former Ministry of Transportation; thus the rarely used official name of the line is the "Number 10 Shinjuku Line" (10号線新宿線, Jū-gō-sen Shinjuku-sen?).
According to the Tokyo Metropolitan Bureau of Transportation, as of June 2009 the Shinjuku Line was the third most crowded subway line in Tokyo, at its peak running at 181% capacity between Nishi-ōjima and Sumiyoshi stations.
Read more about this topic: Toei Shinjuku Line