高速公路匯流區容量分析模式之研究

Models for Capacity Analysis of Freeway Merge Segments

進口匝道匯流區常為高速公路瓶頸所在，臺灣公路容量手冊提供規劃、設計及評估公路容量及服務水準之參考，當中關於匯流區的分析模式是基於有限之現場資料訂定，已無法滿足目前的分析需求。針對國內出現頻率較高之匝道型態，探討獨立匝道、非獨立匝道匯流區段車流運作之影響變數及分析模式，建立適合國內車流情況進口匝道匯流區之容量分析方法。研究發現，主線車道數為三車道時，獨立匝道匯流區的外側兩車道使用主要受加速車道長度及匝道流率所影響；但如上游有一鄰近出口匝道，會導致分析匯流區的外側兩車道使用比例下降。主線車道數為四車道時，外側兩車道使用比例受加速車道長度及匝道流率所影響，較不受上游、下游鄰近匝道所影響。

On-ramp merge segments are usually a traffic bottleneck of the freeway. Taiwan Highway Capacity Manual provides a reference for planning, designing, and evaluating highway capacity and level of service. However, the analysis models for the on-ramp merge area were developed based on limited on-site data, which were unable to meet the current requirements in practice. This study proposes models for capacity analysis of freeway merge segments. Based on the most frequent on-ramp types in the Taiwan freeway system, we establish analysis models for isolated ramps and non-isolated ramps, which consider domestic traffic behaviors. Our results show that when the number of lanes in the mainline is three, the amount of traffic using the outer two lanes is affected by the length of the acceleration lane and the ramp flow rate for an isolated ramp. However, if there is an adjacent ramp upstream, the use ratio of the two outer lanes will decrease. When the number of lanes is four, the use ratio of the two outer lanes is mainly affected by the length of the acceleration lane and the ramp flow rate but not by the presence of adjacent ramps upstream and downstream.