With the rapid expansion of mass transit system, big cities like Shanghai should be able to ease the congestion and pollution caused by an excessive number of cars. But, that is still no easy task.

Statistics show that Shanghai's subway lines will reach 350 km by the end of this year, making the city No 3 in the world in terms of subway length. Shanghai could be ranked No 1 when the length is extended to 430 km next May in time for the World Expo.

This means about 5.5 million people each day could use the city's subway system, thereby reducing traffic bottlenecks and air and noise pollution in downtown Shanghai.