Beijing rolled out new traffic control measures Monday, but they had little effect as the capital's roads remained clogged and a grey smog shrouded the city.

The new measures, which are less strict than curbs used during the Beijing Olympics in August, are aimed at banning the city's 3.3 million cars from the road for one day a week each, based on license plate numbers.

But Beijing Television Station's morning traffic programme showed the capital's streets jammed up as usual, while small accidents around the city ensured gridlock on many roads.

As Monday was the first day of the new system, police were not levying the 100 yuan (13 dollars) fine for drivers violating the ban. The fines will begin next week, local media said.

According to the system, licence plates ending with one or six will be banned from the roads on Monday, plates ending with two and seven on Tuesday, three and eight on Wednesday and so on.

The rules, which only apply from 6:00 am until 9:00 pm and do not include weekends, are also supposed to curb air pollution, but Beijing's normally grey, smoggy sky was on full display Monday.

Despite the gridlock during the morning rush hour, officials insisted the new rules had improved traffic flow.

"Normally the traffic here moves at between 15 and 20 kilometers per hour (nine to 12 miles an hour), today it has been moving as fast as 40 kilometres an hour," a policeman on one of Beijing's ring roads told state television.

Beijing's air is among the most polluted in the world, and the problem is getting worse with about 1,000 new private automobiles bought each day by increasingly affluent city residents.

The tighter Olympic restrictions, which expired on September 20, had limited private motorists to driving on alternate days, removing more than a million vehicles from the streets each day.

The measures led to unusually blue skies. Authorities said atmospheric data showed Beijing enjoyed its best air quality in a decade thanks to the measures.