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Trans. Planning Journal
| Title | Traffic Flow Characteristics in and near the Shea-San Tunnel on National Highway 5 |
|---|---|
| Author | Feng-Bor Lin and Cheng-Wei Su |
| Summary | 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. |
| Vol. | 38 |
| No. | 1 |
| Page | 85 |
| Year | 2009 |
| Month | 4 |
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