With the advancement of wireless technology, vehicular ad hoc networks (VANETs) are emerging as a promising approach to realizing "smart cities" and addressing many important transportation problems such as road safety, efficiency, and convenience. This brief provides an introduction to the large trace data set collected from thousands of taxis and buses in Shanghai, the largest metropolis in China. It also presents the challenges, design issues, performance modeling and evaluation of a wide spectrum of VANET research topics, ranging from realistic vehicular mobility models and opportunistic routing, to real-time vehicle tracking and urban sensing applications. In addition to the latest research and techniques, the reader will also learn the trace-driven methodologies and tools of performance modeling and analysis, network protocol design and optimization, and network simulation, thus keeping pace with the fast moving VANET research and development.