Metro, Subway, MRT, Rapid Transit, U-Bahn, Metrorail — or whatever you like to call it, here's the creative global resource for it. Metrobits.org is a non-profit database, a virtual cube of thousands of data chunks, backed by reliable sources and to a good deal contributed by users. There are two different views on the data:
• categories (menu on the left) compare the world's metros in respect of their various features.
• cities (menu on the right) list all the details for each metro.