What's the busiest metro line in Shanghai?

On Friday, the Shanghai Metro company announced that daily passenger numbers had again broken the daily record, surpassing 6 million. They also provided line-by-line numbers so it's possible to see the numbers of passengers using the different lines:

Clearly Lines 1 and 2 are the most popular, with over 1 million each.  Line 4 and Line 8 are the next most popular. Of the lines which opened in 2010, Line 7 is already seeing almost half a million daily passengers.