In vehicular ad hoc network, due to the frequently changing topology, no available relay node selection may occur and cause low delivery ratios and high end-to-end delays. For improving these problems, a fine packet routing protocol should dynamically adapt to the rapid changing network. Therefore we propose a connectionless routing mechanism called CAME. It is based on geographic routing scheme. Instead of constructing a routing path in advance, we set a reference line from the source to the destination, which is to assist the efficient selections of relay nodes. By utilizing the reference line, we can control the directions of packet dissemination to avoid route loop problems and get the efficient paths for transmissions. Furthermore, we derive a waiting time function and adopt different routing strategies in straight roads and intersections for efficiently selecting the relay nodes. In addition, data flow is considered to avoid fail transmissions due to congestions and disconnections. Extensive simulation results show that CAME has significant performance improvement in comparison with other existing geographic routing schemes.