Abstract. Communication eciency at the transport layer is of specic importance for ad hoc networks. Especially in vehicular ad hoc networks, vehicles will have a temporary and rather short-lived connectivity to the Internet, which has to be utilized eciently. In this paper, we propose a TCP-based transport protocol called MCTP that is optimized for the Internet access in vehicular environments. Therefore, MCTP is combined with split performance enhancing proxy architectures, where a proxy separates the end-to-end TCP connection. This enables the deployment of optimized transport protocols while maintaining interoperability with TCP used in the Internet. For the evaluation, we emulated the communication characteristics of a typical vehicular scenario. This clearly shows the advantages of MCTP over traditional approaches; the overall data throughput is signicantly higher when MCTP is used for communication between vehicle and proxy. The evaluation also emphasizes the usefulness of performance enhancing proxies in vehicular environments.