The Expo may now be firmly in our rearview mirrors, but Shanghai’s infrastructure boom still isn’t finished. The city just announced that an additional 80km of Metro track will be added in the next two years. Shanghai’s Metro system is already the world’s largest subway–why does it keep expanding?

The Shanghai Metro system finished its last major expansion before the Expo, and currently has 273 stations and 420km of track, not including the Maglev rail. This latest extension will spawn two new lines: Line 12 will cut diagonally across the city from Minhang to northeastern Pudong, while Line 13 will connect rural Jiading up north to southeastern Pudong, running past Xintiandi and West Nanjing Lu. Lines 9 and 11 will push further into now mostly barren areas of Pudong, while Line 9 will also go deeper into Songjiang at its other end. By 2020, there will be 22 lines and 877km of track.

Mike Narodovich, an entrepreneur who’s been in Shanghai since 2005, thinks the expansion is worth the hassle. “When I first visited in 2003, there were lines 1, 2 and 3, and that was it. I can’t think of another city where the metropolitan area is this large and as densely packed. Shanghai wants to relieve the pressure by expanding the limits of the city. For example, Jinqiao was nothing in 2000 when my friend Ashley set up the Shanghai Rugby Football Club there, and now it’s the best suburb in town, commercializing faster and faster. Waigaoqiao will be like that by 2015, and it’s out by the ocean!”

However, Barbara Simeles, a Songjiang resident who stands to benefit from the new lines, doesn’t see the point in expanding further into the suburb. “I can’t imagine why they think they need an extension on Line 9. There’s a bus station right next to the University Town stop, so people get off the Metro and hop on a bus if they want to go further. Most of New Songjiang is boring apartment complexes.”

And perhaps that’s the key. As Narodovich tells us, the new lines that have popped up in the last few years have “opened up a lot of places in the city where businesses can move for cheaper rent, because good workers can now get around easily.” With housing costs exploding throughout the city, more and more people are moving out to less densely packed (but no less connected) suburbs, allowing the city to keep booming while relieving ever-present rent pressures downtown.

Is Shanghai's subway getting too big for you? Is it not big enough?