First of all, I don't think inter-airport transfers are especially relevant. Bear in mind that PEK is the second busiest airport in the world; we have flights to many , many destinations.

The issue is that there aren't any more daytime landing slots, and those flights tend to be full.

The city planning people have known that additional airport(s) were going to be required for ~10 years. There had been talk about converting a military airport or two to accommodate commercial service; Nanyuan, in particular, received a lot of attention because KN already uses it, but the road infrastructure in that area is dreadful.

Until this recent news broke, my money was on a site (near Epoch City) between BJ and Tianjin along the train route because that would have served both markets and supported BJ's southward development ambitions.

Just to provide a bit of history, apart from downtown, the NW part of BJ (Haidian) was traditionally considered the most desirable based on its positive fengshui (there is more water up there and the winds tend to come from that direction); that's why most of the universities are up there.

Meanwhile, Chaoyang became desirable during the 1980s because it was opened to foreign investment first (much like Jing'an in Shanghai).

The south, by contrast, was largely ignored and looked down upon.

Well, the times are a changin'. Build a $X billion HSR project with its terminus at South Stn and the largest airport in the world, and you can bet your bottom dollar that massive development will follow. As of now, there is minimal subway coverage in the south, but the worker bees are doing their best to change that:

http://www.beijing-travels.com/beiji...way/plans.html

Even though both the existing airport and the proposed airport are both technically in Beijing, I think it's conceptually easier to think of them as being on opposite ends of an enormous metropolis, similar to SZX/CAN or BWI/IAD.

I'm sorry for the long winded post, but I find this stuff fascinating. What's more, I've been fortunate enough to have had the opportunity to witness this city/country transform from abject poverty into the land of iPhones and Ferraris during the course of the past 1.5 decades. While I realize that the bubble could burst at any time, thus far, things have pretty much adhered to the "5 Year Plans" to a tee (that failed Maglev experiment in SH, notwithstanding).