The passenger capacity will increase by 15 percent on line 2, the busiest line in Shanghai... connecting the city's two airports.  Shanghai Metro authorities said yesterday they will try to shorten intervals along the line by 20 seconds at rush hours. But crowding will remain a problem.

At the same time, Metro authorities said they would limit passenger flow at VERY jammed stations to relieve pressure.

The number of people using the subway system has been growing steadily since May, and could hit 7 million a day. Metro authorties suggest passengers better plan their routes, and take advantage of transfer stations to avoid congestion.