This book presents selected papers of the 6th International Symposium for Intelligent Transportation and Smart City (ITASC) held at Tongji University, Shanghai, on May 16 - 17, 2025. It investigates in detail aspects of intelligent transportation and smart city, mainly focusing on the green traffic and urban utility tunnels. Due to rapid development in the domain of intelligent transportation and smart city, there are many popular topics, such as the 2BMW system (bus, bike, metro, and walking), transportation safety and environment protection, urban utility design and application, and the application of BIM in the city design. It collects dozens of papers and lectures with high quality, including some authoritative scholars and most experienced engineers' latest achievements, which provide guidance to those both in universities and entrepreneurs.