在本问题的求解中，修桥和挖隧道是两个相类似的求解过程，我们将求解过程分为两个部分：第一、对河岸边一固定点 ，将桥修在 处时，求解由起始点 到经固定点 到居民点 的最短路线。第二、如何确定 的位置，使得总路线的费用最小。我们分别用了两个模型来进行这两部分内容的求解。模型一、针对坡度的限制，利用小区域内的局部最优来达到全局最优。模型二、列出点 有一定的位移时，可以减少的费用 的函数方程，然后利用河岸附近等高线较紧密，公路不能沿偏离等高线方向前进的特性，求出减少的费用 的条件极值，从而确定最佳修桥地点 。最后，我们利用模型一、二的原理对隧道部分的公路做了同样的优化设计，然后得出总的修路费用估计为324万元，较合理。最后，我们对整个做法的误差及合理性做了分析。-in solving this problem, building bridges and two tunnels are dug similar to the solution process, we will be solving process is divided into two parts : the first, on the banks of the river a fixed point of the bridge repair in the Department, from the starting point to solve by the fixed point to settlements in the shortest routes. Second, how to determine the location, making the cost of the smallest general line. We were using the two models, both part of the solution. One model, the slope of the restrictions against use of the local small areas to achieve optimum global optimum. Model 2, listing a certain point of displacement, can reduce the cost of the equation, and then using the riverbank near the contours more closely, not along the highway from contour direction of the character