Focusing on the Sino-European cities (Hangzhou, Copenhagen, and Paris), this project aims to provide tools and case studies for optimizing multimodal traffic management, improving urban mobility, reducing traffic emissions, and finding new solutions towards greener mobility practices, climate-neutral and smart cities. Based on big data, smart traffic management technologies, and integrated interdisciplinary methods, this project will build an Integrated Urban System (IUS) and key performance indicators (KPIs) for each city. With evolving urban planning, energy consumption, transport supply and demand, and group behaviours, the system will improve our understanding of interactions among urban multimodal mobility (e.g. biking and trains), traffic emissions (e.g. switch to electric vehicles), air quality and climate change, and quantify these interactions. The results will allow us to quantify the leverage effects observed and to highlight issues of environmental justice. The system will build multi-scenario simulations (e.g. reduced parking space for private cars, promoting public transport, better bicycle infrastructure) and propose multi-mode transport schemes suitable for sustainable development, simultaneously optimizing mobility, and reducing emissions, health and climate risks by introducing KPIs. Through collaborative analyses and cross-simulations, a multi-mode transport scheme suitable for the sustainable development of Sino-European cities is further proposed. Results will establish a model for building smart cities, promoting cooperation, and jointly exploring climate neutrality pathways under future urbanization processes.