1. Department of Automation, Tsinghua National Laboratory for Information Science and Technology (TNlist), Tsinghua University, Beijing 100084, China
2. Key Laboratory of Road and Traffic Engineering of Ministry of Education, Tongji University, Shanghai 201804, China
3. School of Transportation Science and Engineering, Harbin Institute of Technology, Harbin 150001, China
4. Department of Civil & Environmental Engineering, University of Washington, P.O. Box 352700, Seattle, WA 98195, USA