High Quality Content by WIKIPEDIA articles! A metro system is a rapid transit train system. In some cases, metro systems are referred to as subways or undergrounds. The first metro system, the London Underground, was opened in 1863. As of 2010, there are approximately 160 metro systems in the world. The Shanghai Metro is the longest system in passenger route length. The New York City Subway has the most stations and the longest amount of total track, with a total of 842 miles (1,355 km), including non-revenue trackage.