高速公路輔助標誌改變緩坡路段車流之研究

Abstract

緩坡路段(mild gradient)會使得高速公路局部地區容量減小，甚至在坡底形成瓶頸路段。設置輔助標誌提示駕駛人在行經緩坡路段進行加速是近年來十分常用的措施，目的在減少緩坡路段的車速下降，讓車流中的速度差異減小，使車速勻化。本研究針對設置輔助標誌後駕駛人是否真的能接收到資訊，或是在緩坡路段進行加速是否真的能增加臨界流量、減少壅塞的發生，選取國道高速公路緩坡路段歷史資料進行調查分析。研究結果發現，設置輔助標誌後各車道的車速變異量均有下降，顯示車流中的速度差異確實變小。但是內車道與外車道的平均車速也下降，僅有中車道的車速上升；使得整個路段的平均車速下降。而以里程生產量(mileage production)來評估運輸能力後發現，內車道與外車道的臨界運輸能力在設置輔助標誌後均下降，中車道的臨界運輸能力略為上升，整體上來看該路段的運輸能力並沒有因為設置輔助標誌而有提昇。然而因為該路段在設置後的交通量較設置前提昇了約15%，是否因車流量的提昇造成設置輔助標誌後之成效遭稀釋而不明顯，則有待更進一步研究。

Mild gradient leads to the capacity reduction in some sections of the freeways, even forms a bottleneck. Setting up an auxiliary sign to recommend drivers to accelerate while passing the mild gradient is a common treatment in Taiwan for the past few years to reduce the speed drop and narrow the speed differential. This study aims to investigate whether drivers will receive the information and accelerate while passing the mild gradient to improve the capacity. The results find that after setting up auxiliary signs, the speed differential is lower in all traffic lanes. But the average speed is lower than before in overtaking lane and outside lane, leading to an average speed reduction in this experiment section. The mileage production of the overtaking lane and the outside lane are also decreased. In conclusion, the transportation ability of this section is not improved after installing the auxiliary signs. However, it should be noted that the traffic volume had increased 15% over the study period. It might cause the speed reduction and dilute the effects from these auxiliary signs.