The research presented in this paper develops and quantifies the fuel savings associated with an ecodrive system that combines an ecocruise control algorithm and state-of-the-art car-following models. The system makes use of topographic information provided from a high-resolution map, the spacing between the subject and lead vehicle that can be obtained from a radar system or some form of vehicle-to-vehicle communication, a desired (or target) vehicle speed, a minimum and maximum desired speed, and a cruise control spacing threshold. The study demonstrates that the proposed system can significantly improve vehicle fuel efficiency without significantly increasing the intervehicle spacing. Specifically, fuel savings in the range of 27% are achieved with an average vehicle spacing of 47 m along a study section of Interstate 81. The study also demonstrates that regular vehicles can benefit significantly by following a lead ecodrive vehicle.