Abstract: In urban vehicular ad hoc networks, due to the complex and dynamic traffic conditions and the diversity of driving routes, the network topology changes quickly and the communication links between vehicles are unstable, which affect the data forwarding performance of the vehicular networks. As an important public transportation facility in cities, buses have regular driving routes and departure time, and bus lines cover urban streets widely. Compared with private cars, buses are better data carriers and forwarders, and are helpful to achieve more reliable vehicle-to-vehicle communication. This paper proposes a bus-data-driven forwarding scheme for urban vehicular networks, called BUF, which aims to improve the transmission efficiency of urban vehicular networks by analyzing bus line data and selecting appropriate buses as forwarding nodes. First, a bus stop topology graph is constructed, in which all bus stops in the scenario are vertices and an edge links two vertices if there exist bus lines continuously passing through these two stops. The cost of an edge is computed based on the expected number of buses and the distance between two stops. Then the optimal forwarding path from the source stop to the destination stop is calculated by using Dijkstra algorithm. Moreover, in order to ensure that the data is forwarded along the optimal path, the neighbor backbone buses, whose overlapping degrees of subsequent stops with the optimal path are greater than zero, take priority to be selected as the forwarding nodes; and the greater the overlapping degree is, the higher priority the bus has to forward data. When no backbone bus exists, the neighbor buses, which will pass the expected next stop, called the supplement buses, are selected as relays. In the scenarios without backbone or supplement buses, private cars are used to establish a multi-hop link to find a suitable bus forwarder, in order to accelerate data forwarding. Experimental results with real Beijing road network and bus line data show that compared with other schemes, our BUF scheme achieves higher data delivery rate and shorter delay.