Guangdong province's special economic zone Shenzhen, which has the mainland's highest vehicle density, is looking at strategies to decongest its clogged roads.

More than 1.7 million vehicles had been registered in the city as of Dec 8, approaching the official limit. But there are actually more than 1.9 million vehicles, in addition to cars from outside the city, Shenzhen traffic department figures show.

Shenzhen's average driving speed was 36.3 kilometers an hour on major highways and roads by the end of last year, compared to 40.7 km an hour by the end of 2008.

The downtown speed dropped to an average of about 10 km an hour, which is equivalent to the average bicycle's speed.

Taxi driver Liu Chengwen said the clogging of the roads has hurt business.

"Almost all of the streets are jammed on holidays," Liu said.

Rather than limit vehicle registrations, the government will prioritize "green public traffic systems", Shenzhen's Party Secretary Wang Rong said.

The city invested more than 45.8 billion yuan ($6.9 billion) to improve the traffic system this year, Deputy Mayor Zhang Siping said.

The city will have six subway lines spanning 178 km by the end of June, he said.

Some experts suggested adopting traffic easing techniques used in Hong Kong.

Zhang Jian, a lawyer from the Shenzhen Branch of Beijing Dacheng Law Office, said marketing means might prove most effective. The low cost of car ownership is driving the increase in private vehicles, Zhang said.

A resident who has purchased a car for less than 100,000 yuan usually spends less than 1,500 yuan a month on parking fees, tolls and gasoline. So the volume of private cars in Shenzhen has continued growing at about 10 percent annually.

But Hong Kong residents usually pay about 10,000 yuan for a car's monthly operation.

Zhang said Shenzhen could up the ante by introducing expensive parking and congestion fees.