This paper proposes a road side unit (RSU)-coordinated synchronous multi-channel medium access control(MAC) scheme for vehicular ad hoc networks (VANETs). Theproposed scheme allows the on board unit (OBU) to reserveservice channels (SCHs) on the control channel (CCH) duringalmost the whole synchronous interval and supports simultaneoustransmissions on different SCHs. It enhances the performanceof VANETs and decreases the CCH congestion. Moreover, weuse RSU to record the rendezvous information and broadcastit to the OBUs. This method avoids the multi-channel hiddenterminal problem. An analytical model is developed to evaluatethe aggregate throughput on SCHs. This model takes intoaccount the following factors: non-safety message transmissionprobability in each synchronous interval, average size of thenon-safety message, and the number of OBUs. Furthermore, therequirement of obtaining the maximum throughput is computed.Simulation results are provided to validate the analytical modeland to demonstrate the improvement in throughput. The resultsindicate that the proposed scheme can provide higher aggregatethroughput than that of the Vehicular Enhanced Multi-channelMAC (VEMMAC) and IEEE 1609.4, and better performancein CCH congestion control especially under high network loadconditions.