Source: adapted from Metrobits.org, World Metro Database.
Approximately 194 subway (metro) systems are in operation worldwide, with several carrying more than 1 billion passengers per year. The construction and setting of subway systems have accelerated in recent years, particularly in cities in developing economies where mass transit has become a clear strategy to improve urban mobility and mitigate congestion. China and India are the most salient examples. The level of ridership is linked with several geographical and economic considerations. Some cities with high ridership, such as Moscow, Beijing, and Shanghai, have a tradition of subsidized public transportation and transit-oriented urban planning.
Many high-density cities have a level of subway ridership proportional to their population (London, Hong Kong, Osaka, Paris, Seoul, and Tokyo), indicating a consistent level of ridership where public transit accounts for between 25% and 50% of commuting. Cities, where ridership is proportionally less than the population, have either a significant portion of their population living in poverty and using less formal transit systems or are wealthy enough to prefer the automobile.