For the realization of the safe driving support system in the Intelligent Transport System (ITS), many studies are conducted to apply the wireless ad hoc network to the inter-vehicle communication. In the wireless ad hoc network protocol used for the inter-vehicle communication, it is necessary to consider the stability of route because network topology changes dynamically according to movement of vehicles. Flow Route Oriented Protocol (FORP) is suitable for such case because Route Expiration Time (RET) that is the index of the route stability is used when the route is decided. However, there is a problem of FORP that the amount of control traffic is comparatively large because the node should broadcast the Route Request (RREQ) packet even when the stability of the link that composes the route is low. In this paper, we propose an improvement method of FORP to reduce routing traffic. To evaluate the performance of improved FORP (iFORP), we implemented FORP and iFORP in a network simulator. From simulation results, iFORP shows the better performance than the FORP.