As the number of vehicle miles traveled each year continues to increase, traffic congestion only worsens, and the need for accurate, timely traffic information becomes stronger. With recent advances in technology, a growing number of vehicles are now equipped with wireless communication systems and global positioning satellite (GPS) sensors. Using such vehicles as mobile traffic probes has the promise of accurate and timely information without large infrastructure and construction expenses. To address some of the basic design and feasibility questions for the concept of using probe vehicles to provide real-time traffic information, an analytical model was developed that examines the relationships between key system parameters. The results of this modeling show that a real-time traffic information system based on probe vehicles is very feasible, and should work for freeways at penetrations over 3%, while surface roads would require more than 5%. With the increased use of in-vehicle telematics, these levels of penetration are likely to be achievable.