A central tenet of sustainability is to efficiently utilize all resources. In order to fully utilize the surface transportation system, it is essential that all involved have access to accurate, complete information in order to make sound decisions. Infrastructure providers must have knowledge of traffic conditions in order to better use control mechanisms (such as traffic signals and ramp meters), as well as react to events (such as incidents). Furthermore, travelers must have access to traffic conditions in order to travel as efficiently as possible, not wasting energy, for example, stuck in congestion. Unfortunately, the availability of comprehensive, accurate real-time traffic information has been limited. However, recent research and development has led to the use of probe-based traffic monitoring techniques. Using existing information technologies, such as wireless communications and global positioning systems, it is now feasible to derive traffic monitoring data over a wide area at reasonable costs. This seminar explores the research foundation that has led to this important development in surface transportation.