高速公路幾何設計極繁複且需大量運算，多設計線公路之平面線形則由於須同時考量兩兩設計線於空間中之相對關係而更為複雜，此類問題又以交流道匝道系統之平面線形設計為最。由於其複雜性，以人工設計要完全滿足各種規定已屬難事，更無法有系統地尋找優良設計，故多設計線平面線形最佳化設計的數學模式與高效率的求解方法，對降低設計成本及幾何設計自動化極為重要。本研究所探討之主題為交流道平面線形設計問題，旨在建立一個以基因演算法 (Genetic Algorithm) 為基礎之交流道平面線形最佳化模式，利用其廣域搜尋的優點，求得滿足規範要求之優良交流道平面線形。
文中首先分析組成匝道平面線形之基本元素 (包含直線、緩和曲線以及圓弧) 之組合型態，經歸納後發現一匝道之平面線形在任兩連續反曲點間基本元素之組合具有一定之規則。本研究根據此規則，依平面線形之局部曲率半徑變化情形，重新定義四種平面線形設計元素，並以此構建基因演算法架構中之基本元件 (包含基因、染色體、基因運算子以及適合度函數等) 與求解交流道平面線形之基礎模式。
交流道平面線形之設計除考慮運輸需求、環境限制以及行車安全順暢外，亦會對交流道之整體外觀有所要求。因此，為提供設計者操控交流道平面線形設計結果之空間，本研究設計一套設計者參數，將其架構於基礎模式上，構建設計模式。設計模式可讓設計者對單一匝道本身、兩兩匝道之間或是兩匝道群之間指定所需之特殊設定。而為增加設計模式之彈性，本研究另外提出兩個具不同求解策略之設計模式，分別為雙母體演化設計模式與回饋式設計模式。
最後，由模式驗證的結果可知，本研究所提出的最佳化模式的確可以有效率地設計高速公路交流道的平面線形。

The work of highway geometric design is very complicated and consumes significant labor, time, and cost. The design of the horizontal alignments of an interchange system is even more complex because the relativities of any two alignments in the system need to be considered simultaneously. Obtaining a feasible solution to meet all code requirements manually for engineers is difficult, let alone a systematical search for better designs. In order to reduce design cost and enable automatic computerized design to search for better solutions, it is necessary to develop mathematical models to solve for the optimized geometric design of the horizontal alignments of a multi-lined highway system. This research proposes an optimazation model based on the genetic algorithm for getting a good solution that satisfies all constrains in the design of the horizontal alignment for an interchange.
By analyzing the basic elements (including tangent line, clothoid curve and circular curve) for the horizontal alignment of ramps and cumulating the regularity of the basic elements between inflection points, we define four new ramp element types according to the variation of the curvature radius along the horizontal alignment. We also define components for the genetic algorithm including gene, chromosome, gene operators and fitness functions, and develop a model for solving interchange horizontal alignments.
In additional to traffic demand, environment restrictions and safety, the appearance of the interchange is considerded in the interchange horizontal alignments. The resulting model combines the basic model and a set of designer parameters, and provides a means for designers to determine settings on a single ramp or relationships between any two ramps or any two groups of ramps when necessary. Besides, in order to increase the flexibility of the design model, two extensions with different solving stratages, “Two-population evolution design model” and “Feed back design model”, are also proposed in this research.
Testing results suggest that the model and heuristic can determine horizontal layouts of interchanges correctly and efficiently.

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