In this paper we study the impact of RF jamming on 802.11p carto-car communications. We build a jammer on a software defined radio and implement constant, reactive and pilot jamming patterns, whose effectiveness is first measured in an anechoic chamber. We perform extensive experiments in two relevant outdoor scenarios, namely a straight road in an open space as well as a dense building scenario with a crossroad and characterize the performance of 802.11p communications under the impact of constant and reactive RF jamming. The constant jammer is able to dramatically disrupt communication regardless of the scenario. The reactive jammer exhibits a low impact in scenarios with reduced line-ofsight as its jamming success greatly depends on the relative position of the nodes. It is, however, very effective in open-space scenarios. In general, we observe that RF jamming can cause large communication-blind areas. Under these conditions, critical safety applications would simply fail in their purpose of timely warning dissemination.