In this paper, a hybrid communication paradigm for vehicular networking is presented in which connectivity is provided by both existing network infrastructure (e.g. wireless network access points) through a vehicle-to-infrastructure protocol and traditional vehicle-to-vehicle networking. Pre-existing infrastructure can provide seamless connectivity, especially when vehicles are sparse or travelling in disconnected neighbourhoods, while vehicular communications are available for dense traffic scenarios. In this vision, we depict a novel heterogeneous vehicular network scenario, in which overlapping wireless networks partially cover the vehicular grid. Vehicle-to-X (V2X) is based on a protocol switching decision, which is achieved in a distributed fashion by each vehicle based on a cost function using path alternatives. An analytical model for protocol switching in V2X is described. Moreover, we analyse how messages are forwarded by vehicles communicating via V2X. We characterise the maximum and minimum bounds of information propagation and compare performance with traditional message propagation based on opportunistic networking.