“…The number of motor vehicles has also increased significantly, from 42 million in 1997 to 145 million in 2006. In addition, the length of express highways nearly tripled in just 6 years, from 19,500 km in 2001 to 53,000 km in 2007 (Zhang et al 2010). In early 2009, China became the world's largest automobile market, surpassing the United States for the first time in total car sales (Overholt 2010).…”