In London, the 2022 debut of a transit line stretching the width of the metropolis quickly attracted more than half a million riders per day and promptly lifted the entire UK’s rail ridership above pre-pandemic levels. In Seoul, a blazing-fast subway that can exceed 100 miles (161 kilometers) per hour has cut travel times from the southern suburbs to the central business district by a factor of four. In Delhi, a similar system is under construction that will ultimately allow passengers to travel 100 km across the crowded megacity in just one hour.

New York University finance professor Arpit Gupta calls this emerging class of transit “rapid regional rail.” Think of these systems as mass transit for a megalopolis: They travel faster and farther than traditional urban metros like the New York City subway, and operate far more frequently and seamlessly than typical suburban commuter rail services like the Long Island Rail Road. Their function is “to reduce the length of commutes into urban areas to greatly expand the travelsheds around cities and increase their effective size,” Gupta wrote in a recent Substack post.