— In this paper we present empirical results from a study examining the effects of antenna diversity and placement on vehicle-to-vehicle link performance in vehicular ad hoc networks. The experiments use roofand in-vehicle mounted omni-directional antennas and IEEE 802.11a radios operating in the 5GHz band, which is of interest for planned inter-vehicular communication standards. Our main findings are two-fold. First, we show that radio reception performance is sensitive to antenna placement in the 5Ghz band. Second, our results show that, surprisingly, a packet level selection diversity scheme using multiple antennas and radios, Multi-Radio Packet Selection (MRPS), improves performance not only in a fading channel but also in line-of-sight conditions. This is due to propagation being affected by car geometry, leading to the highly non-uniform antenna patterns. These patterns are very sensitive to the exact antenna position on the roof, for example at a transmit power of 40mW the li...