BEIJING -- Beijing is likely to trial a congestion charge on road users, the city's traffic authority said on Thursday.

"We are looking into the possibility of a congestion fee in certain areas," said Zhou Zhengyu, director of Beijing transport commission.

Beijing will further tighten its traffic controls, and deliberate policies that will encourage companies to adopt different working hours, Zhou said.

Close to 5.6 million vehicles vie for space on Beijing's roads. This means that vehicles have just 18.3 square meters of road each; slightly larger than a parking space.

Vehicle emissions account for 31 percent of the city's smog sources, according to Beijing Environmental Protection Bureau.

Beijing has rolled out various policies to address air quality and congestion, such as restricting vehicles from using the roads on one out of five weekdays based upon the last digits on their license plates.

Congestion fees are charged in Singapore and London, among others.