混合車流下圓環儀控方法研究

由於圓環(Roundabout)的在路口中特性為兼具安全及在中低流量下的紓解效率高，因此一直以來流行於歐洲國家。而近年來，美國朝向道路節食(Road diet)及開始增設圓環的方向發展、日本也開始推廣無號誌圓環路口。可見圓環路口是現代交通工程的發展趨勢。然而，台灣的都會區交通具有相當高的汽機車混合比及私人運具旅次佔比，不利於圓環的發展。本研究針對尖峰車流特性明顯之路口來設置儀控圓環，希望能夠透過儀控的方式來增加圓環的整體容量，並且在一般時間處於無號誌圓環狀態，減少設置為號誌路口的延滯浪費，一併解決延滯及路口安全問題。拓展無號誌圓環相對於號誌路口的可適用性，提升將路口設計為圓環的誘因。本研究探討在尖峰時間不平衡車流的條件下，透過佔有率法進行演算，並且以VisVAP 來撰寫圓環儀控策略，在不過度影響幹道車流的前提下，提供幹道車流下游受影響車輛足夠的時間間距進入圓環，降低延滯及排隊長度，增加整體的紓解效率。本研究亦討論適合的最小空白時間及最小儀控時間，做為降低對幹道車流的影響及增加支道車流紓解量兩者之間的取捨探討。藉由嚴格的模型校估驗證後，來證明此模擬法具有可信度，再進行多種不同的需求比、轉向比及混合比情境分析，以及儀控圓環、無號誌圓環及一般號誌十字路口模擬比較。透過類似於佔有率匝道儀控法的模型，本研究分析各種情境下的平均每車延滯及最大排隊長度的績效結果，發現相對於無號誌圓環此圓環儀控不管在任何混合比皆能夠在僅些微影響幹道車流延滯的條件下大幅降低支道車流及整體路口的延滯，因而降低號誌路口設計為圓環的門檻。

關鍵字

無號誌路口；儀控圓環；佔有率法；混合車流；車流模擬

並列摘要

Roundabout has been popular in European countries because it provides more safety and efficient functions at low and medium flow rates. In recent years, the US has begun to promote road diet concept and build more roundabout; Japan also started to install this intersection type in suburban area. It can be seen that roundabout has become one of the recent trends in traffic design in the global. However, it’s harder to develop roundabout in Taiwan due to the serious mixed traffic flow situation and high percent mode share to private vehicle. In this study, the implement of roundabout metering strategy is set up for solving the intersection with higher peak hour factor and is hoped to increase the overall capacity. Also, it reduces vehicle delay and becomes much safer than signalized junction in off-peak conditions. This implement helps expand the applicability for roundabout. This research uses VisVAP to explore roundabout metering method by occupancy strategy. The goal is to creates larger gaps for downstream entrant vehicles to decrease the overall vehicle delay and queue length with limited negative impact on the main roads. This study also discusses the minimum blank time and minimum metering time to appropriate balance the impact between main road and the downstream entrant. The simulation model is proved to have credibility and reliability after rigorous model calibration and validation. The three scenarios which were metering roundabout, unsignalized roundabout and normal signalized junction were simulated in different demand ratio, mixed traffic flow ratio and turning ratio composition for analysis. By analyzing the average vehicle delay and maximum queue length performances with roundabout metering strategy, the results show that roundabout metering can significantly reduce overall vehicle delay and queue length under every mixed traffic ratio combination and only has slightly negative effect on main road.