Vehicular ad hoc networks, known as VANETs, are deployed to improve passenger comfort as well as to reduce the risk of road accidents by allowing vehicles to provide a warning in real time when a critical event is detected. In such networks, communication is possible both between the vehicles themselves and between the vehicles and the infrastructure. These applications need a reliable and secure broadcast system that takes into consideration the security issues in VANETs, the high speed of nodes, and the strict QoS requirements. For these reasons, the authors propose a trust-based and centralized TDMA-based MAC protocol that avoids time slot assignment to malicious nodes and minimizes message collision. The solution is based on the design of a generic trust mechanism for VANETs based on the MAC requirements and its integration into a centralized TDMA-based MAC protocol, named trust-CTMAC. The mechanism will permit roadside units (RSUs) to manage trust level assignment via security check during free slot allotment. The experiments carried out and the results obtained prove the effectiveness of the approach.