左轉保護時相可以提供左轉停等車在不受對向直行車之衝突造成阻礙或延滯狀況下，而能陸續地進行疏解，通常又稱之為無衝突左轉。停等車之疏解行為受到現場幾何設計、交通特性與號誌狀況的影響，但國內對於無衝突左轉停等車疏解行為之研究並不多。本研究針對此一議題，共蒐集15個車道18,771個樣本現場資料，經分析發現，利用傳統飽和流率的觀念並不適合用以估計此車道或車道群容量，而改採用2001年臺灣地區公路容量手冊所建議之直接估計方法，則較為精確、實用。本研究另發現第四部以後停等車之平均疏解車距受到左轉速率與左轉運行區域之縱向距離所影響，大車與迴轉小車相對於左轉小車之pce分別是1.98及1.30。本研究並建立綠燈時段及燈號轉換時段能疏解車輛數之推估公式，比較與討論二、三左轉車道之疏解特性。本研究之成果可提供分析無衝突左轉車道容量之參考。

Protected left-turn phase, the so-called unopposed left turns, provide left-turn vehicles to discharge continuously under the situation with no conflicts of opposing through vehicles. The discharge behaviors of queuing vehicles are affected by geometric designs, traffic characteristic, and signal conditions. However, few domestic studies have focused on the queue discharge behaviors of unopposed left-turn vehicles. This study aims at this issue and collects field data amounted to 15 lanes and 18,771 samples. Data analyses showed that the traditional methodology used by saturation flow rate is inadequate estimating the capacity of these lanes or lane group. To improve the accuracy of the estimated capacity, this study used the direct estimating method suggested by 2001 Taiwan HCM. In addition, the average discharge headway after the fourth vehicle in queue is affected by left-turn speed and longitudinal distance of left-turn moving area. The passenger-car-equivalent of large vehicles and U-turn vehicles relative to left-turn passenger cars are 1.98 and 1.30, respectively. The formula for estimating the number of discharge vehicles in green and inter-green intervals is built. We also compared and discussed the queuing discharging behaviors of each lane in cases of 2 left-turn and 3 left-turn lanes. The results of this study could be referenced for estimating the capacity of unopposed left-turn lanes.