Safety applications exploiting Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) based on Vehicular Ad hoc Networks (VANETs) have made great impact on research and development in ITS. The successful delivery of the periodical safety-related beacons is the key to security of the vehicular group. To better achieve this goal, the MAC protocol has to be highly reliable and has to assure certain fairness among vehicles. In this paper, an overload tolerant TDMA (OLT-TDMA) mechanism is proposed to ensure the fairness of channel access as well as a good Quality of Service (QoS). The simulation results show that the OLT-TDMA scheme outperforms the traditional IEEE 802.11p protocol, especially in very dense traffic scenario.