In this paper, a User-Based model is proposed to analyze and evaluate the performance of IEEE 802.11p MAC protocol for vehicular safety applications that can save lives and improve traffic flow. The proposed model uses a powerful result from the theory of regenerative processes, in effect, to reduce the problem of defining a Markovian model to the problem of determining the steady-state moments of the delay process. Its simplicity, together with its operational properties, provide the means for the stability analysis of 802.11p MAC protocol comparing to the Markovian models which usually give insufficient information on the stability. This stability analysis can provide us opportunities to further investigate the design parameters of 802.11p MAC, leading to an optimization methodology which indicates how IEEE 802.11p should be configured for improved performance. We established a relation between the Finite and Infinite user population model and investigated the performance of the protocol when the two population models are adopted; the IEEE 802.11p can meet the needed latency and reliability requirements for the delivery of safety messages under the Finite user model, however, it fails to satisfy such requirements under the Infinite user model. Our results show that IEEE 802.11p MAC has a tradeoff between the acceptable delays and the acceptable loss in traffic and this tradeoff is only determined by the peculiarity of the safety application.