After spending some time in Beijing, I decided that LA and BJ should be sister cities. They share many important characteristics of modern cities: traffic, sprawl, and smog. The first two are linked, of course, and contribute significantly to the third.
One noticeable change in China since the first time I went (in 2001) is that the number of cars has increased dramatically. In 2001, bicycles still outnumbered cars in Beijing. In 2007, cars vastly outnumber bicycles.