1. Institute of Urban Transport Planning; China Academy of Urban Planning and Design; 5 West CheGongZhuang Road Beijing 100037 China
2. Key Laboratory of Road and Traffic Engineering of the Ministry of Education; Tongji University; 4800 Cao'an Road Shanghai 201804 China
3. Department of Civil and Environmental Engineering; Utah State University; Logan UT 84322-4110 U.S.A.