High Speed Uplink Packet Access (HSUPA) is an extension of the Universal Mobile Telecommunications System (UMTS) technology of 3GPP Rel-99, with the objective increasing the data rate (up to 5.76 Mbps) and reducing the latency of the uplink. 3GPP UMTS standard Rel-6 introduces a new "Enhanced Dedicated Channel" (EDCH) for the uplink. The main focus of the work presented in this paper is to analyse the effect of TNL congestion control on the HSUPA performance. The congestion control function works together with the scheduler and HARQ functionality in order to control the offered load to the TNL network. In this manner, the data flow over the transport network (TNL) is adequately controlled and limited to the available TNL capacity by avoiding congestion in the transport network. The TNL congestion control consists of two independent parts: congestion detection and congestion control which have been implemented, tested and validated within the focus of this paper. The simulation results presented in this paper confirm that the congestion in the transport network can be controlled in such a way that the available TNL capacity can be effectively utilised and hence the performance of HSUPA network can be significantly improved in all aspects.