Private railways in Tokyo are too complicated to understand.
When you arrive at Shinjuku Station by JR, please transfer to a private railway.
I work for one of the major private railway companies in Japan.
A private iron (remember how 鉄 often has to do with railroad tracks and the like? Same goes here) is a private railway. There are a good number of these in Japan.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.