The Shanghai Metro is the world's longest metro network at 803 kilometres (499 mi) and has the highest annual ridership at 2.83 billion trips. The New York City Subway has the greatest number of stations with 472. As of 2023, the country with the most metro systems is China, with 45 in operation.

When measuring by the number of individual stations and the physical complexity of the network, New York City is the global leader with 472 stations across its sprawling subway system. However, if you define the "most" underground trains by the total length of the tracks, Shanghai and Beijing have both surpassed New York in recent years, each boasting over 800 kilometers of metro lines. Shanghai's network is often cited as the largest and most modern in the world, moving nearly 10 million passengers on a typical weekday. If you look at the "density" and frequency of trains, the London Underground (the oldest in the world) and the Tokyo Metro are frequently the top contenders, with Tokyo's Shinjuku station acting as the world's busiest transit hub. These massive networks are the lifeblood of their respective megacities, utilizing thousands of individual train cars and sophisticated automated signaling systems to maintain headways of just two minutes during peak rush hours, reflecting the sheer scale of modern urban engineering.