Subways are the only way to do an old, dense city, plus you get a network effect as you increase the network density, especially if you have an integrated ticketing system.

Beijing is a challenging city because it's old, short, and broad. Few buildings are taller than 4 stories, and so it has a very large footprint. Subway stops tend to be very far apart -- so far that if your destination is on the same road as the subway but halfway between the two nearest stops, you might well take a taxi to finish the trip.

Because it's so sprawling, there's more roads. But, each driver also has to drive farther to get from their A to their B. Bikes are still somewhat popular, but again, the distances from A to B make it less attractive than in the much denser Shanghai.

I'm thrilled that Beijing is spending money on their subway -- it's a post WWII relic of a system, and the people of Beijing will benefit tremendously from the investment. Hopefully Beijing will restrict the addition of parking garages too... if there's no place to put a car, there's no way to own it.

The first thing they ought to do is build an underground nuclear reactor to power the subway. It would also supply artificial geo-thermal heat to buildings.

Downtown Chicago once had an underground railway system that could connect to the basement of many buildings for delivery of coal and supplies and removal of trash. With modern tunneling machines, any city could have many tunnels including small subways with a stop every few hundred feet. Automatic street cars could also run on rails between main subway stops. or perhaps they would be elevated monorails. Somewhere on the web the linear motor personal transportation system can be found. ..HG..