The continual increase in vehicle parc and stricter restrictions on energy consumption regulations have posed substantial challenges for vehicle energy conservation and emission reduction. Three pillars, namely networking, intelligence, and electrification, could improve the efficiency of transportation, energy conservation, and emission reduction in the future. Considering the frontier problems and research progress of energy saving and emission reduction in the context of intelligent connected vehicles, a general overview of current key issues in the field of eco-driving is presented. First, from the perspective of energy conversion in a broad sense, this paper summarizes the essence and three processes of energy-saving approaches in intelligent vehicles, wherein wheels to distance optimization in the vehicle systems is the most important. The basic mathematical principles of energy-saving optimization in terms of wheel-to-distance are introduced. Second, considering diverse non-homologous and heterogeneous data of intelligent transportation systems, various sources of intelligent information are described from three aspects: human-vehicle interaction, vehicle-to-vehicle communication, and vehicle-road perception. Third, for a single vehicle in an intelligent networked environment, aiming at the key issue of the combination of multi-dimensional information and advanced control technologies, specific applications are discussed from four aspects: predictive cruise control considering road slope, predictive cruise control for car-following conditions, engine start/stop and neutral taxiing, and lane change. For the human-vehicle-road-cloud under a multi-source heterogeneous environment, aiming at the key scientific issue of collaborative energy-savings based on vehicle behaviors, the research status is clarified from four aspects: eco-driving, collaborative energy saving of multiple vehicles, collaborative energy saving at road intersections, and collaborative energy saving based on vehicle-cloud. Furthermore, pioneering research on electric highway systems is described in detail to elaborate on the future trend of collaborative energy saving in the context of intelligent heavy commercial vehicles. Finally, the importance of intelligent information for improving the energy-saving performance of intelligent connected vehicles is summarized, and the challenges that may be encountered at the theoretical and practical levels are discussed. © 2021, Editorial Department of China Journal of Highway and Transport. All right reserved.
