Using transit buses as probes to detect general vehicle traffic conditions could be a real-time traffic monitoring mechanism in an urban advanced traveler information system. The feasibility of such an application depends primarily on the existence of quantifiable relationships between bus traffic and general vehicle traffic and infrequent bus travel observations (constrained by the scheduled bus headway and route configuration) that are sufficiently sensitive to infer real-time general vehicle traffic conditions. Considering that urban bus probe studies have focused only on the first criterion, this study is designed to examine real-time sensitivity between buses and cars. A generic framework of real-time urban travel time estimation is proposed, followed by a field study in which real-time bus travel information is available and a simulation study that examines the impact of passenger demand on performance of the proposed framework. The study findings provide insights into the feasibility of a real bus probe application in an urban traffic environment. Future studies are desired to explore bus probe performance in nonrecurrent traffic congestion.