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The deployment of short-range high bit rate radios on city buses enables a number of ubiquitous sensing applications. In this paper, we focus on data forwarding in such applications. We make an empirical study on traces from a real city bus system, where we try to explore unique features of the bus-based delay tolerant sensor networks (DTSN) that can affect the data forwarding. We carefully examine the encounter behaviors both at the bus-level and the route-level and show that the route-level encounter behaviors exhibit a trend that is quite predictable. Based on the finds, we propose a novel data forwarding scheme named R2R (Route-to-Route) which leverages the route-level encounter frequency as the metric to plan a path for each message. Then, each message is forwarded along the planned path to a destination route. Trace-driven emulations are developed to evaluate the proposed R2R, in which we compare it with several schemes. We show that R2R achieves a good performance in message delivery rate and buffer consumption.