Providing Internet access on buses allow people to read news, check emails, watch sport games, and hence can greatly improve the quality of people's life. This paper proposes an adaptive routing protocol, called R-BUS for a bus network. R-BUS selects a route based on the link's lifetime and its communication signal quality. The protocol takes the bus mobility and the radio propagation model into account. A real map scenario is employed to evaluate the performance through simulation. The simulations show that R-BUS can guarantee the communication quality and also increase the route reliability. Compared to the existing routing protocols, R-BUS can achieve higher packet delivery ratio, lower average packet delay and lower control overhead.