This paper addresses the problem of using standard EDCA to minimize frame collisions among periodic vehicle safety messages. We make two principal contributions. First we demonstrate an Access Category (AC) isolation technique that dramatically reduces the collision probability of high priority packets in dense environments. Second we introduce a novel concept called virtual division by which significant reductions in collisions among lower priority packets can be achieved. AC isolation and virtual division are conformant with IEEE 802.11p and can be supported by existing integrated circuit implementations, but to the authors' knowledge neither has been published before. These techniques are motivated by the periodic safety message environment under development in the US, Europe and parts of Asia, but they may have applicability for other vehicular applications or more general WiFi networks. The results in this paper are verified via extensive NS-2 simulations.