探討機車專用道容量問題，必須先了解機車之疏解特性，但由於國內先前有關的研究，未考量專用道分隔方式 (如標線或實體分隔) 之差異，且未說明機車專用道寬度如何量測，亦未適當交代取樣之週期數，以致於沒有具體的共通成果，實務上難以運用。因此，本研究錄影蒐集臺北市八個機車專用道的現場資料，其原始車道寬介於 1.7 ~ 3.4公尺間，每個調查地點至少有 50個週期，以停止線為基準線，記錄停等機車後輪通過基準線之橫向位置軌跡，並提出以α截集的觀念來決定「實際使用疏解寬度」；同時，計算分析每 2秒之機車疏解率。分析結果顯示： (1)將 α 訂為 0.05時，所得之實際使用疏解寬度可有效地作為估計飽和流率之參數，故八處調查地點的實際使用疏解寬度在 1.3 ~ 3.4公尺之間； (2)各車道疏解率在綠燈啟亮後 10秒開始平穩，顯示所調查之機車 專用道存在飽和流率；(3)飽和流率隨著實際使用疏解寬度的增加而明顯地增加；(4)經利用實際使用疏解寬度 (W，公尺) 及其飽和流率 (S，機車／小時)，可建立推估式 S = 6168.6 + 441.9W2，其判定係數 (R2) 為 0.88且參數均顯著，本研究進一步應用於估計不同綠燈時段下之容量。這些研究成果可以提供未來設置機車專用道之參考。

The characteristics of motorbike discharge behaviors are very important for the analysis of the capacity of exclusive motorbike lanes. However, previous researches disregarded the influences of different separation types (i.e. road marking or physical separation) and did not illustrate the methods of measuring lane-width, and the numbers of sampling cycles as well. The findings in previous studies were inconsistent and impractical. This study collected field data using cameras at eight sites with lane-widths ranging from 1.7 to 3.4 meters in Taipei city, with more than 50 cycles at each site. Researchers recorded the horizontal positions of back-wheels of motorbikes passing the reference line, which was identified as a stop line, and determined the actual discharge-width by an α-percentage cutting rule. In the meantime, the numbers of discharged motorbikes were counted every 2 seconds. The findings of this study were summarized as follows. (1) The value of α was 0.05 because the corresponding actual discharge-width could be effective in estimating saturation flow rates. The actual discharge widths at these eight sites ranged from 1.3 to 3.4 meters. (2) The discharge rates became stable 10 seconds after green light turned on. It showed that the saturation flow rate exists. (3) It was found that the saturation flow rates clearly increased when the available lane widths widened. (4) Based on the available lane-width (W, meters) and the corresponding saturation flow rate (S, motorbikes/hr), a simple regression model was estimated as S = 6168.6 + 441.9W2. The coefficient of determination (R2) was 0.90 with all estimated parameters being statistically significant. Furthermore, this study estimated the capacities under various green intervals based on the estimated saturation flow rates. The results of this study are essential for setting up exclusive motorbike lanes in the future.