Developing Design Guidelines for Passing Lanes in Taiwan
DAI M, CHEN W and HSU F, National Cheng Kung University, Taiwan
Rural two-lane highways constitute the predominant mileage of highway systems in Taiwan. Most of them are designed with low standards. As the increase of traffic and the ageing of roads, the service levels deteriorate significantly. Funds are limited when
Rural two-lane highways constitute the predominant mileage of highway systems in Taiwan. Most of them are designed with low standards. As the increase of traffic and the ageing of roads, the service levels deteriorate significantly. Funds are limited when compared with the extensiveness of the two-lane highway system. In addition, the construction costs are extremely high for some two-lane highways in mountainous area, and hence it is very unlikely to upgrade these roads to four-lane highways at one time. For example, the estimated cost for upgrading State Route 9 (SR 9) to a four-lane highway is more than NT$ 22 billion (US$ 800 million). Therefore, how to effectively improve two-lane highways with low-cost modifications becomes an important issue.
Passing lanes are chosen as a solution for improving the service level of two-lane highways in Taiwan. A passing lane is defined as an auxiliary lane provided on a two-lane highway to enhance passing opportunities. The service levels of two-lane highways are strongly dependent on the available passing oppommities. The passing opportunities may be limited by restricted sight distance, insufficient gaps in the opposing traffic stream or slow-moving vehicles. The lack of passing opportunities will causo an increase in platooning and hence driver frustration.
This study tried to develop a methodology for designing passing lanes in Taiwan. A principle for developing the methodology is that it should be easy to use and flexible. It is observed that the performance of passing lanes is affected by many factors. These factors include the traffic conditions and geometrics in the upstream, downstream and lane sites. Therefore, it is a huge combinatorial problem to develop a general design methodology for obtaining optimal passing lane system. In addition, the optimal design of passing lanes should always incorporate the factor of construction costs. However, the construction costs depend on site-specific characteristics.
A comprehensive literature review has been conducted in this research. TRARR simulation model was selected for evaluating the performance of passing lanes. The measure of effectiveness is percent of following in this study. A 4 second headway is used to define a platoon.
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