This article presents various traffic separation approaches to transmit HSPA (HSDPA/HSUPA) traffic in the existing ATM-based UMTS Radio Access Network, together with Release 99 (R99) traffic. The traffic separation technique enables QoS differentiations of HSPA and R99 traffic, while aiming to achieve a maximum utilization of the transport resources in the radio access network. The potential benefit of applying traffic separation and its impact on the performance of the transport network as well as the end users are explored in this article. The quantitative evaluations are provided by simulations. The results presented are obtained from a UMTS simulation model developed in this work which can transmit HSDPA and HSUPA traffic as well as R99 traffic simultaneously. The presented results demonstrate that applying traffic separation between HSPA and R99 traffic can considerably improve the performance of both HSPA and R99 traffic, and as well bring significant gain on efficient bandwidth utilization.