目前國內針對橋梁上機車的自由車流速率之研究相當欠缺，因此本研究乃針對臺北市及新北市間的五座重要橋梁，進行機車道自由車流速率的現場調查與分析工作，以探究機車於橋梁上的行駛特性。本研究運用旅行時間調查之方法，先在橋梁上選擇一段平直的測速區間，並架設兩台錄影機紀錄機車通過測速區間所需的時間，再以區間距離除以機車通過時間求得機車的旅行速率。經由現場資料分析，建議以車距 (headway) 超過3秒以上作為自由旅行機車之認定基礎，因為車距3 秒以上的機車平均速率開始趨於穩定，且與其他更長的車距分組無顯著差異。經K-S檢定法與Q-Q plot均顯示各橋梁的機車自由車流速率為常態分配。五座橋梁上機車平均自由車流速率在速限均為40公里/小時的情況下，竟高達52.6~56.8公里/小時之間，並有高達85.1%~93.0%的機車超速行駛。本研究亦發現橋梁上機車自由車流速率與車道寬有低度正相關，自由車流速率會隨著車道寬增加而增加。本研究之研究成果可進一步了解臺灣橋梁機車行駛特性以及未來作為區間速率執法之參考。

The current research on the free-flow speed of motorcycle on bridges is rather lacking. Therefore, this study is aimed at the five important bridges between Taipei City and New Taipei City, and conducts field investigation and analysis of the free-flow speed characteristics of the motorcycles on the bridges. This study uses the travel time survey method to collect motorcycle travel speed data. Firstly, it selected a straight and flat section on the bridge. Secondly, it set up two time-synchronized video recorders to record the time required for the motorcycle pass the section. Thirdly, it used the section distance divided the travel time to obtain the motorcycle sectional average speed data. It is suggested to use the headway for more than 3 seconds to define a motorcycle travel on free-flow situation or not by field data analysis. The average motorcycle speed with a headway more than 3 seconds begins to stabilize, and there is no significant different with other longer headway groups. And, all motorcycle free-flow speeds are distributed as normal distribution by K-S test and Q-Q plot. The average motorcycle free-flow speeds on the five bridges are as high as 52.6~56.8 km/h with a speed limit of 40 km/h, and there are as many as 85.1%~93.0% motorcycles speeding. The study also found that the motorcycle free-flow speed on the bridge is positively correlated with the lane width, and the free-flow speed increases with the increase of the lane width. The research results of this study can further understand the motorcycle driving characteristics of Taiwan's bridge and the future as a reference for sectional average speed enforcement.