1. Tao Tao. Qinghai transportation science and technology, 2011, (4): 1-5. (In Chinese).
2. Liang Du. Economic Research Guide, 2011, 13: 142-145. (In Chinese).
3. Liang Ge, Hongxi Xin and Jun Ma. Highway, 2006(6): 20-23. (In Chinese).
4. Dengying Jiang, Canhua Kang, Zuomin Li. Journal Of WuHan University Of Technology, 2009, 31(1): 144-148. (In Chinese).
5. Weidong Li, Jiaqiong Wang. Journal Transportation Systems Engineering and Information Technology, 2005, 5(3): 9-13. (In Chinese).