Active transit signal priority (TSP) is a useful tool to remove or minimize control delay for buses at signalized intersections and consequently improve the performance of bus service. Conditional TSP has been proofed to be an effective measure with fewer impacts to non-prioritized traffic, and aroused increasingly research interests and implementation in European and North American cities nowadays. However, the implementation of conditional TSP requires a sophisticated mechanism for examining

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... he schedule deviation of priority required buses, as well as scanning traffic operational conditions at network level. By contrast, unconditional TSP is a less costly and easier measure for implementation, because it gives priority to every required bus without considering its schedule deviation. The critical argument on unconditional TSP is its adverse impacts to non-prioritized traffic, particularly during peak hours. To determine the threshold for implementing unconditional TSP, in this paper, theoretical analysis based on signal display graphs of differential TSP granting strategies was undertaken to estimate delay savings and increments for prioritized and nonprioritized approaches respectively. In the next step, Dalian BRT line was taken as an example to verify the feasibility of unconditional TSP based on the proposed theory. Results show that unconditional TSP is feasible during off-peak hours, while for peak hours, feasibility of unconditional TSP mainly depended on the traffic volume of each approach.