How many kilometres long is the world’s largest metro network?

How to get close to this number

Estimate from the city rather than from the railway. A metro has to reach across a metropolitan area of tens of millions of people, with lines crossing it in several directions plus suburban extensions. Add up a dozen or so lines each tens of kilometres long and the total network runs into the hundreds of kilometres, which is the right order of magnitude.

The expectation trap is assuming the answer must be an old European system. London and New York have the longest histories, but history is not length: the systems that are largest today were mostly built recently, at speed, in cities that grew fast enough to need them all at once. As the explanation notes, Shanghai built in thirty years what took London well over a century.

Be careful what is being measured. Route length, track length and line length are three different numbers, and networks are ranked differently depending on which one a source uses, on whether suburban rail operated by the same authority counts, and on how many extensions opened between the survey and today. This is one of the faster-moving infrastructure figures on the site, which is why the year matters.