Nowadays, Device-to-Device (D2D) communication in LTE system has been proposed as a possible candidate for vehicle-to-vehicle(V2V) communication. As V2V communications share the same licensed frequency spectrum pool with typical UEs communications in one LTE cell, efficient radio resource allocation is a challenging issue. In this paper, we proposed a traffic flow based dynamic resource allocation algorithm for vehicular communication networks, which could make radio resource to be utilized in a more efficient way with a flexible node-grouping algorithm. The simulation results show, compared with random allocation and greedy allocation algorithms, the proposed algorithm can significantly reduce running time and significantly improve spectrum utilization efficiency.