1. Department of Mathematics, Southwest University of Science and Technology, Mianyang, 621010 Sichuan, China
2. Department of Civil Engineering, University of Hong Kong, Hong Kong, China
3. Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, 200072 Shanghai, China
4. Department of Transportation Engineering, TOD-based Sustainable Urban Transportation Center, Ajou University, Suwon 442-749, Republic of Korea