This paper studies how the interference of vehicular communications affects the safety of vehicles in a vehicular ad hoc network. Different signal propagation models with and without carrier sensing are considered for the dissemination of periodic safety messages. Then, by employing the results for different packet success probability of the vehicles, we compare the expected collision probability of vehicles for different signal fading models. Our results show how the collision probabilities of vehicles in the network vary with respect to different models and designs.