This
list of metro systems includes electrified
rapid transit train systems worldwide. In some cases, metro systems are referred to as
subways,
U-Bahns or
undergrounds. , 148 cities in 55 countries around the world host the approximately 160 metro systems that are listed here. The earliest metro system, the
London Underground, first opened as an "underground railway" in 1863; its first electrified underground line opened in 1890, making the London Underground the world's first metro system. The metro system with the longest
route length is the
Shanghai Metro; the busiest one is the
Beijing Subway; and the one with the most stations is the
New York City Subway.