國道5號雪山隧道車流特性之研究

TRAFFIC FLOW CHARACTERISTICS IN AND NEAR THE SHEA-SAN TUNNEL ON NATIONAL HIGHWAY

雪山隧道長度12.9公里，是國道5號高速公路上最長的隧道，也是世界第六長之公路隧道。此隧道有兩個單向孔道，且每孔道有2個車道。在雪山隧道中及國道5號其他路段上設置很多的車輛偵測器，不停的收集交通狀況資料。為了確保行車安全，國道高速公路局對雪山隧道內變換車道、速限、最小跟車間距及何種車種能進入隧道均有明文規定。到目前為止，國道高速公路局已各將速限及車種的限制調整過一次。從95年6月通車至今，這些交通控制策略的演變及大量的偵測器在隧道內外收集到的交通特性資料，提供了一難得探討長隧道內車流特性及交通控制策略影響的機會。此外，臺灣交通界亦有需要評估雪山隧道之作業績效以謀求改善策略。因此，本研究的目的在於了解雪山隧道在速限為70公里／小時，而且只有小車能通行時的車流特性。分析之資料為民國96年9月及10月中偵測器所收集的資料。分析結果顯示雪山隧道4個車道的平均容量大約只有1,000小車／小時／車道。此容量遠低於一般快速公路及多車道公路之容量，這低容量的主要因素，很可能是現行法規要求在正常狀況下跟車間距最少必須保持50公尺之規定。

With a length of 12.9 km, the Shea-San Tunnel is the longest tunnel on Taiwan’s National Highway 5 and the sixth longest highway tunnel in the world. The tunnel has two one-way tubes. Each tube has two lanes. Inside the tubes and in other sections of the National Highway 5, there are a number of vehicle detectors that collect traffic data. The Bureau of National Freeway Management has implemented a series of traffic control measures to ensure traffic safety in the tunnel. These measures regulate lane-changing, speed limit, minimum car-following distance, and the use of the tunnel by various types of vehicles. So far, the Bureau has revised the speed limit and the control of access to the tunnel once. This evolution of control measures and the availability of a large number of vehicle detectors provided a rare opportunity to explore the traffic characteristics and the impact of changes in traffic control in a long tunnel. There is also a need to assess the operating efficiency of the tunnel to identify areas that need improvement. The objective of this study is to provide an understanding of the capabilities and the deficiencies of the traffic operation of the Shea-San Tunnel when the speed limit in this tunnel is 70 km/h and only small vehicles can enter the tunnel. To this end, the traffic data collected by the detectors in September and October 2007 are analyzed. The analysis shows that the four traffic lanes in the tunnel have an average capacity of only about 1,000 small vehicles per hour per lane. This capacity is extremely low in comparison with that of a lane of either a typical freeway or a multilane highway. The minimum car-following distance (50 meters) requirement is potentially the most significant cause of the low operating efficiency.