Rush hour traffic jams are a daily occurence in large cities all over the world. These traffic jams result in congested roadways and highly dense network topologies. VANET medium access mechanisms need to be very efficient in order to cope with such events. In this paper we analyze the suitability of HIPERLAN Type 1 s EY-NPMA medium access protocol for high density VANETs. We compare its performance with an IEEE 802.11 based system, in terms of delay, throughput and delivery ratio. Our simulations in NS-3 show that EY-NPMA is quite stable, provides satisfactory delay and throughput and maintains a high delivery ratio in medium to high load conditions. We conclude that it might be very suitable for traffic jam scenarios.