Contraflow bus lanes have been implemented in Taipei City since February 1990. Related works have analyzed effects of this bus priority strategy. This paper presents new evidence of the impacts of the contraflow bus lanes on bus ridership. A time-series model is developed for this evaluation. The study focuses on one bus line, whose structure changed little when the contraflow bus lane was implemented. General information of the bus priority strategy is provided. Monthly ridership data were collected. Box-Jenkins modeling techniques are used to forecast the ridership that would have resulted if the contraflow lane is not implemented. Effects of the contraflow bus lane on ridership are identified by comparing the forecasted ridership with actual ridership. Results in this study show that ridership of the bus line assessed significanltly increased about 28.5 percent after the contraflow bus lane had implemented. Current trends of this significant effect are also explored.