High reliability and low latency are crucial requirements for vehicular safety applications. We have previously proposed a media access control (MAC) protocol for a roadside-to-vehicle communication (RVC) system using narrow antenna beam switching with multiple antenna beams to increase reliability even in a shadowing region. In this paper, we describe transmission performance evaluation of an RVC system with antenna beam switching based on a traffic flow model using computer simulation. Simulation results show that our proposed technique can reduce the packet error rate (PER) of the system with a single broad antenna beam in an environment where surrounding objects reflect waves.