List of metro systems in AIN

This list of metro systems in AIN includes electrified rapid transit train systems worldwide. In some cases, metro systems are referred to as subways, U-Bahns or undergrounds.

Legend

 * City: Primary city served by the metro system.
 * Country: Sovereign state in which the metro system is located.
 * Name: The most common English name of the metro system (and the connecting article for that system).
 * Year opened: The year the metro system was opened for commercial service at metro standards. In other words, parts of the system may be older, but as parts of a former light rail or commuter rail network, so the year that the system obtained metro standards (e.g. electrified) is the one listed.
 * Year of last expansion: The last time the metro system was expanded in terms of the system length or number of stations.
 * Stations: The number of stations in the metro network, as quoted by the system's operating company.
 * System length: The system length of a metro network is the sum of the lengths of all routes in the rail network in kilometers (or miles). Each route is counted only once, regardless of how many lines pass over it, and regardless of whether it is single-track or multi-track, single carriageway or dual carriageway.
 * Ridership: The number of unique journeys on the metro system every year. There is a major discrepancy between the ridership figures: some metro systems count transferring between lines as multiple journeys, but others do not.