Intelligent Transportation Systems (ITSs) have been exploited by developed countries to enhance the quality of transportation services. However, these systems are still facing major bottlenecks to be addressed such as the data density, precision and reliability of perceived data and computational feasibility of the nodes. Trust management is a mechanism applied to secure the vehicular networks. However, most of the proposed trust models that are applied to Vehicular Ad-hoc NETwork (VANET) do not address all the aforementioned challenges of ITS. In this paper, we present a comprehensive framework of trust management specifically designed for ITS applications. The proposed framework is an infrastructure-based solution that relies on Smart Road Signs (SRSs) to assess the trustworthiness of traffic data and nodes of the network. The idea of the framework is to use autonomous SRSss that are able to collect raw data and evaluate it in order to alert the drivers with reliable traffic information in real time. We adopt a hierarchical architecture that exploits a two-level trust evaluation to ensure accuracy, scalability, security and high reactivity of ITS applications. A discussion of the framework and its strengths is presented.