This paper aims to analyze two major quantities related to the performances of IEEE 802.11p based Vehicle Ad hoc NETwork (VANET): the mean number of simultaneous transmitters and the distribution of the distance between them. The first quantity is directly related to the network capacity as it limits the number of frames transmitted in the network at the same time. The second quantity is a crucial element to describe interference generated by the simultaneous transmitters and to deduce important wireless properties such as the Signal on Noise plus Interference ratio, Bit Error Rate or the Frame Error Rate. We propose two different models to approach these quantities: an extension of the R´enyi's packing model and a Markovian point process. Our theoretical propositions are compared to simulations performance with the network simulator ns-3 and show good agreement. In addition, we have also incorporated two new models in ns-3. The radio model has been set according to real experimentations. These experimentations involved two vehicles equipped with IEEE 802.11p wireless cards. Also, we used a realistic vehicles traffic simulator, emulating highway traffic, that we have combined with ns-3.