With the 2008 Olympics coming up in Beijing, there's a lot of talk about air quality and traffic in the capital of China.
One thousand new cars go on the road in Beijing every day, joining the three to four million cars that are already jamming the streets and threatening public health.
Breath the air in Beijing and you're breathing the world's highest levels of lung-damaging nitrous oxide, according to a recent study. As well las a lot of particulates.
So China is facing a big challenge: how to move people without choking them.