There's gridlock coming in the next fifteen years: according to the recently released Beijing Traffic Development Outline, by 2020 there will be 5 million private cars on the roads in Beijing, or about 1 for every 1.2 households.
There are about 2.35 million private cars in Beijing at present; that number is expected to reach 3.8 million (or 1 for every 2 households) by 2010.
To deal with the traffic, the authorities will be introducing an exciting new multipass-like card for use in public transportation and taxis. They will also be constructing new north-south arteries, expanding rail and bus lines, and introducing street-level light-rail trains 40 years after streetcars disappeared.
Links (in Chinese):
Beijing Evening News via Sina, article
Mirror article on the light rail, with pictures