China is holding a No Car Day in more than 100 cities as it tries to reduce smog ahead of the 2008 Summer Olympics.
Drivers in Beijing disregarded appeals to leave their cars at home
Cars have been banned on some central streets in Beijing and all drivers are being encouraged to leave their cars at home voluntarily.
But correspondents say that in the capital National No Car Day appears to be making little impact.
Millions of vehicles are on the roads every day in Beijing, causing massive air pollution.
The BBC's James Reynolds in Beijing says that cars are coming and going as normal, and most streets in Beijing are not adhering to No Car Day.
Environmental campaigners say China must overhaul its transport system, not just with a few ad hoc No Car Days but by putting in cycle lanes, reducing the price of public transport and making it much more difficult for people to buy private cars.
But China has a huge incentive - not just the health of its citizens, but the success of the Olympic Games in August next year.
The head of the International Olympic Committee (IOC) has already warned that if the pollution is bad next summer, some endurance events - such as cycling or the marathon - may have to be postponed.