In urban vehicular networks, Road-Side Units (RSUs) take a crucial role in improving the performance of the network, by working as content distribution points, relays for time-critical broadcasts, and points of central coordination. The high costs associated with the installation and maintenance of RSUs, however, keep these units from seeing widespread deployment. One approach to this problem is for cars to be used opportunistically as RSUs, and in urban areas, the presence of large numbers of parked cars make these entities promising candidates for establishing vehicular support networks. In this paper we introduce new methods for parked cars to self-organize and act as a support network to the existing urban vehicular network, alleviating the need for costly deployments of fixed road-side units. Our approach considers parked cars that can both complement existing fixed RSUs and take the role of RSUs themselves, improving the network’s performance on multiple applications. We show that even a small number of parked cars can bring considerable improvements to the network, and that our proposed methods for self-organization create support networks of parked cars that can cover the urban area with an optimal numbers of vehicles.