The zone routing protocol based on bus backbone networks can reduce network congestion caused by routing protocols such as common used table-driven routing protocols for urban traffic applications. However, there are a lot of redundant communication in the external cluster discovery phase of the routing protocol, which increases routing overhead. In order to reduce routing overhead, an improved regional routing protocol based on bus backbone networks is proposed. The improved routing protocol adds two fields to the link state update packet of the traditional zone routing protocol for storing the location information of the cluster head node and the destination node. In the external cluster discovery phase, the position constraint equation is constructed according to the position information of the cluster head node and the destination node. It is used to select the reasonable peripheral nodes to carry out data forwarding task and eliminate the redundant communication of other peripheral nodes. The simulation results show that the packet loss ratio, end-to-end average delay and routing overhead of the improved routing protocol are better than the zone routing protocol based on bus backbone network. The comprehensive performance metrics are also superior to two common used routing protocols such as AODV and DSDV.