A vehicular backbone network (VBN) has the potential to augment the Internet with high-throughput data flows for delay-tolerant traffic. High-throughput flows require a joint utilization of transportation capacity for carrying data packets through physical mobility and wireless capacity for switching data packets from one route to another. This paper establishes a model that incorporates both transportation mobility and wireless switching. Then, it characterizes the network capacity based on flow conservation, wireless communication capacity constraints and data storage limits, and solves a convex optimization that results in joint routing and congestion control. A variant with cost minimization reduces delay while maximizing throughput. Next, this paper develops a distributed algorithm that achieves the global objective with limited infrastructure support. Lastly, a packet-level simulation platform using real-world road map and traffic statistics is used to evaluate the distributed algorithm, and demonstrate the significant performance enhancement achieved.