Eco-driving is a driving style that can significantly reduce fuel consumption and CO2 emissions. However, current methods for eco-driving practice are inefficient or inaccessible, and of little appeal to the next generation of eco-safe drivers. Therefore, we built iCO2, a networked multiuser three-dimensional (3D) eco-driving training environment, where multiple users can practice eco-safe driving in a shared simulation space in both cooperative and competitive ways.