China will invest a total ¥993.73 billion ($1 = ¥6.83) in 89 metro networks of 2,500km in length through 2016. Currently there are 10 cities running 31 metro lines covering 835.5km on the mainland, and the number of total lines and length are expected to hit 55 and 1,500km by 2010. A mainland city has to meet the following three requirements to build a metro system: three million in population, ¥100 billion worth of GDP and ¥10 billion in local government revenue. Shanghai's 500-plus km metro network, the nation's largest, is projected to have a six million daily ridership taking up 35% of public transport traffic by 2010.