In conventional road-vehicle communication systems, user terminals in the vehicles have to directly connect with wireless access points (APs). However, the speed of vehicles is so fast that the channel condition between the terminals and the APs constantly changes because of changing pathloss and time-varying fading. In this paper, to compensate for such deterioration, we propose to reduce relative speed between user terminals and APs by using an inter-vehicle packet relay technique. If a terminal can send or receive data via other vehicles running at lower speeds, the relative speed will decrease, which suppresses the dynamic range of path loss and deterioration by fading. We evaluate our method by computer simulations using a geometric propagation model. In the simulations, phase difference between multiple paths and path-loss fluctuation within one frame duration affect the performance. From the results of the simulations, we validate our method. Moreover, we evaluate interference in the overlapped zone between two AP areas. From the evaluation, we show that our packet relays do not cause a problem in interference between areas.