GUANGZHOU - 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.