 Since the mid-2000s, the growth of rapid transit systems in Chinese cities has rapidly accelerated, with most of the world's new subway mileage in the past decade opening in China.From 2009 to 2015, China built 87 mass transit rail lines, totaling , in 25 cities at the cost of ¥988.6 billion.In 2016, the Chinese government lowered the minimum population criteria for a city to start planning a metro system from 3 million to 1.5 million residents.