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In order to reduce transit (bus or tram) delays at intersections and protect them from the effects of growing traffic congestion and hence make them more attractive and more reliable, the transit priority strategy (such as transit lane concept and transit priority treatment measures) is widely applied at signalized junctions.As each signalised junction is different, the same bus priority method may give different results. It is quite difficult to quantify the transit priority performance and its consequences in a general way. Based on experiences of junction geometry design, signal design with transit priority treatment and controller programming for more than fifty signalised junctions in Geneva, the author tries to develop a method to evaluate quantitatively transit priority performance and to estimate its impact on non - transit traffic in junction geometry design and junction signal design.In the junction geometry design step, two new definitions, "transit greenable length" and "transit priority performance ratio", are introduced. It is shown that the average transit delay depends on them and formulas to estimate the average transit delays (without transit priority treatment) are developed. Then the transit priority performance of "transit lane concept" at a signalised junction is analysed.In the junction signal design step, different transit priority treatment measures can be applied so that the signal green interval for a transit movement matches the transit arriving interval and the transit delay will be minimised. Trie choice of transit priority treatment measures in different signal designs is discussed.In summary, a good junction geometry design taking account of transit priority performance will limit transit average delay. A good signal design combined with a good junction geometry design and suitable transit priority treatments may considerately decrease transit delay.Therefore a high-transit-priority-performance signalised junction should have a high transit priority performance ratio, suitable transit priority treatments and acceptable impact to nontransit traffic. Finally, some further researches are suggested.