In this paper, we develop an efficient vehicle collision avoidance strategy for intelligent transport systems. The proposed strategy first clusters vehicles according to the features of their movement (e.g., direction of movement, inter-vehicle distance, and relative velocity). To enhance the responsiveness of the proposed CCA system, a risk-aware MAC protocol is designed. In the proposed scheme, an emergency level is defined for each vehicle based on its order in its respective cluster. The emergency level reflects the risk of a vehicle to meet an emergency situation in the platoon. The medium access delay of each vehicle is set as a function of its emergency level in a way that enables vehicles in emergency situations to promptly disseminate warning messages to neighboring vehicles and to accordingly minimize chain collisions. The proposed CCA system is dubbed Clusterbased Risk-Aware CCA (C-RACCA). The performance of the proposed C-RACCA system is evaluated via simulations and encouraging results are obtained.