We discuss here a scheme to improve the Rel'99 UMTS radio resource management. The article focuses on the two different types of transport channel: shared and dedicated. It evaluates the merits of a scheme based on an optimal non real-time session switching between these two kinds of channels. The switching decision may be influenced by several parameters like the downswitch timer's duration, the non-/preemptive split of downswitch timer and the selection of the initial transport channel. Performances of the analysed scheme are evaluated taking into account different metrics: blocking rate, mean packet delay and cell throughput. The results show that an optimal tuning of these three parameters may significantly decrease the number of blocked calls while keeping the other metrics at a satisfactory level.