By Michael Bristow
BBC News, Beijing
Beijing is noticeably less congested following the start of a four-day scheme to take 1.3 million vehicles off the road.
Officials hope to repeat the test next year during the Olympics to reduce traffic on the capital's jammed roads.
They also hope to ease the notorious air pollution, which can reduce visibility to a few hundred metres.
Officials expected the ban would cut vehicle emissions by 40%, although thick smog hung over Beijing on Friday.
City residents, who are being forced to take public transport during the test period, generally appeared to support the pilot project.
"Of course I back the scheme. It's all to do with the Olympics. If there are traffic jams it won't benefit the Games," says computer designer Zhang Yan.
"Although it will be a little inconvenient, it's not that hard to use public transport. There are taxis, buses and the subway," he adds.
Mr Zhang usually drives the short distance from his home to work, both located in east Beijing, but plans to take a taxi over the next few days.
Beijing, home to about 16 million people, has just over 3 million registered vehicles, mostly comprising private cars, buses, taxis and government vehicles.
More than 1,000 new vehicles are registered every day, according to the city's transport authorities. And the pace of registration is quickening.
This has quickly turned Beijing from a place once dominated by bicycles into a car-orientated city. Six-lane highways cut through the city.
Vehicles often edge forward at something approaching walking pace during rush hour, which sometimes seems to last the whole day.
Beijing's road builders have been unable to keep up with the increasing number of cars, said another driver, Zhou Ye.
"There are bound to be traffic jams during the Olympics if nothing is done," adds the 37-year-old architect, who is going to take a taxi to work while he cannot drive.
During the test period, odd-numbered cars will be banned on Saturday and Monday, while cars with even-numbered registrations must stay off the roads on Friday and Sunday.
Any driver caught contravening the restrictions will be fined 100 yuan ($13, £6.50) by 6,500 police officers, many stationed at road entrances.
Police vehicles, fire engines, ambulances and several other categories of vehicles are exempt from the ban, which runs from 0600 to midnight.
Hundreds of extra buses are running, most taxis will operate and the subway will stay opening later than usual.
A similar experiment was carried out last year during a forum for African leaders held in Beijing.
During that period, even shops were told not to receive deliveries during the day.
The car ban is part of a wider project to reduce congestion ahead of the Olympics by improving Beijing's public transport network.
Construction workers are currently completing six new subway and light railway lines, one linking Olympic venues with the city centre.
Air quality at the Olympics is also an issue.
International Olympic Committee President Jacques Rogge said recently that events could be postponed if pollution is too bad.
Residents generally seem to support this current ban, but it will be harder for Beijing to devise a more permanent solution to the city's growing car problem.
Beijing people love their cars, with many choosing to drive to work even though it would be just as quick to ride a bicycle or walk.
This test period will last just four days, and includes a weekend. Residents might be less welcoming of a more permanent ban.