Despite the government's efforts to promote public transportation, heavy traffic still congested Beijing's major roads on Monday - World Car Free Day - prompting calls from transport experts for more concrete efforts to develop public transportation.

The traffic performance index for Beijing roads reached 8.6 at about 8:30 am, indicating heavy traffic congestion, and the average speed of vehicles was only 21.3 km per hour, according to the Beijing Transportation Commission.

The TPI inside the Second Ring Road was 9.6, with an average speed of 16.8 km per hour, the commission said.