中央實體分隔路型停等車疏解能力之坡度調整因素

THE GRADE ADJUSTMENT FACTOR OF QUEUE DISCHARGE BEHAVIOR ON DIVIDED URBAN STREETS

臺灣有一些市區道路利用地下道或高架道路來降低交通衝突。這些地下道通常不長且其上坡終點下游通常緊鄰號誌化路口，而高架道路的下匝道下坡終點也通常緊鄰號誌化路口。這些路口的停等車疏解特性及其車道容量很可能受到緊鄰地下道或高架道路下匝道坡度的影響。目前臺灣公路容量手冊（以下簡稱HCM）係利用坡度調整因素來估計車道疏解能力因坡度之影響情形，但此調整因素並未依據臺灣本土交通特性。本研究主要針對臺灣市區常見之「中央實體分隔、無快慢分隔、無緊鄰公車專用道」路型，進行現場資料蒐集7個不同車道的現場資料。研究成果顯示停止線上游的平均坡度確實明顯影響停等車疏解能力，且影響程度高於美國HCM的數值。本研究並提出此路型之坡度調整因素（fg）迴歸式。

Many urban streets in Taiwan have underpasses or viaducts to minimize conflicting traffic movements. These underpasses are generally short and include a signalized intersection at the upgrade end. Similarly, the off-ramps of viaducts usually include a signalized intersection at its downgrade end. The queue discharge characteristics at such intersections and the resulting lane capacities may be affected by the grades of the adjacent underpasses or off-ramps of viaducts. The Taiwan Highway Capacity Manual (HCM) applies a grade adjustment factor to the estimated queue discharge rate of a level traffic lane to assess the impact of grades. But the adjustment factors used in this manual are not based on the traffic characteristics in Taiwan. Focusing on intersections located on urban streets that have median barriers without exclusive bus lanes and divided express and local lanes, the researchers of the present study collected and analyzed the queue discharge data of seven lanes. Results showed that the approach grade at an intersection had a significant impact on queue discharge rate and that the impact was greater than that indicated in the HCM published by the U.S. Transportation Research Board. The present study proposed a regression model for this road type to estimate the grade adjustment factor (fg).