In this paper a new method to evaluate the network-wide effect of transit signal priority (TSP) is presented. A delay function is developed to estimate the effect of TSP at intersections using parameters such as traffic flow and signal characteristics. The proposed method is tested in two case studies. Firstly, it is applied to a single intersection to address both TSP strategy and model efficiency. Secondly, a set of TSP implementation scenarios is defined for a corridor in SouthEast Queensland, Australia. Bus and car delays are calculated for each scenario and the results are compared with those obtained using microsimulation. The results confirm that the delay estimated by the proposed method closely matches microsimulation results. The proposed method reflects the effects of having TSP at each intersection without performing time consuming microsimulation analyses. This method makes it possible to evaluate the effectiveness of TSP in large networks. The new method can be used to perform preliminary evaluation of TSP schemes at the network level, thereby potentially reducing the significant computational time of network analyses.