th It is our great privilege and honor to present the proceedings of the 18 International Symposium on Transportation and Traffic Theory (ISTTT), held at The Hong Kong Polytechnic University in Hong Kong, China on 16-18 July 2009. th The 18 ISTTT is jointly organized by the Hong Kong Society for Transportation Studies and Department of Civil and Structural Engineering of The Hong Kong Polytechnic University. The ISTTT series is the main gathering for the world s transportation and traffic theorists, and those who are interested in contributing to or gaining a deep understanding of traffic and...