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1、对于闪光灯，很多人是恐惧的。同时驾驭两三灯，甚至五灯，的确是很难。但是如果仅仅只是一灯的话，问题就简单很多。更何况即便是，一人一灯Lesson 27HIGHWAY ENGINEERING 公 路 工 程对于闪光灯，很多人是恐惧的。同时驾驭两三灯，甚至五灯，的确是很难。但是如果仅仅只是一灯的话，问题就简单很多。更何况即便是，一人一灯Transportation has always been one of the most important aspects of civil engineering. One of the greatest accomplishments of Roman en
2、gineers was the high way system that made rapid communication possible between Rome and the provinces of the empire. Modern highways are built according to the principles laid down in the eighteenth and early nineteenth centuries. Generally speaking, alignment, subgrade, and pavement are the most ba
3、sic three parts of the modern highways.交通一直是土木工程中最重要的方面之一。一位罗马工程 师的最伟大的成就是公路体系，其使快速通讯成为可能。现 代公路的修建是根据十八和十九世纪初所定下的原则。一般 而言，线性，路基，路面是现代公路的最基本的三个部分。 IntroductionIntroductionaccomplishment成就 alignment线性 subgrade路基 pavemen路面对于闪光灯，很多人是恐惧的。同时驾驭两三灯，甚至五灯，的确是很难。但是如果仅仅只是一灯的话，问题就简单很多。更何况即便是，一人一灯The alignment of
4、 a road includes horizontal alignment and vertical alignment. The horizontal alignment of a road is shown on the plan view and is a series of straight lines called tangents connected by circular curves. In modern practice it is common to interpose transition or spiral curves between tangents and cir
5、cular curves. So the elements of the horizontal alignment are tangent, circular curve, and transition curve, as shown in following Fig. 27-1. 公路线形包括平面线形和纵断面线形。道路的平面线形显示在平面图和一系列的直线称为圆曲线连接切线。目前在实际操作中，一般在切线和圆曲线之间插入缓 和曲线或螺旋曲线。平面线形的组成是切线（直），圆曲线和 过渡曲线，如图中下面的图27-1。1.Alignment（线形）horizontal alignment平面线形 ve
6、rtical alignment纵断面线形 tangent切线 circular curve圆曲线对于闪光灯，很多人是恐惧的。同时驾驭两三灯，甚至五灯，的确是很难。但是如果仅仅只是一灯的话，问题就简单很多。更何况即便是，一人一灯对于闪光灯，很多人是恐惧的。同时驾驭两三灯，甚至五灯，的确是很难。但是如果仅仅只是一灯的话，问题就简单很多。更何况即便是，一人一灯Curve lineStraight line对于闪光灯，很多人是恐惧的。同时驾驭两三灯，甚至五灯，的确是很难。但是如果仅仅只是一灯的话，问题就简单很多。更何况即便是，一人一灯The vertical alignment of a road
7、is shown on the cutaway view. The elements of the vertical alignment are tangents, vertical curves. Usually there are two type of vertical curve: convex vertical curve and concave vertical curve, as shown in following Fig. 27-2.道路的纵断面线形显示在剖视图。纵断面线形的组成是切线，竖曲线。通常 有两种类型的竖曲线：垂直凸竖曲线和 凹竖曲线，如图以下所示27-2。cuta
8、way 剖面 convex 凸的 concave 凹的对于闪光灯，很多人是恐惧的。同时驾驭两三灯，甚至五灯，的确是很难。但是如果仅仅只是一灯的话，问题就简单很多。更何况即便是，一人一灯对于闪光灯，很多人是恐惧的。同时驾驭两三灯，甚至五灯，的确是很难。但是如果仅仅只是一灯的话，问题就简单很多。更何况即便是，一人一灯Alignment must be consistent. Sudden changes from flat to sharp curves and long tangents followed by sharp curves must be avoided; otherwise, a
9、ccident hazards will be created. Likewise, placing circular curves of different radii end to end(compound curves) or having a short tangent between two curves is poor practice unless suitable transitions between them are provided. 线形必须一致（平面线形和纵断面线形）。必须避免平地突然变化为急弯以及很长的切线后紧跟着锐曲线，否则 就会产生事故风险。同样地把不同半径的圆
10、曲线尾尾相连 、或两条曲线之间插入短切线是不良做法，除非曲线之间 有适当的缓和曲线。 consistent一致 likewise同样地 radii半径对于闪光灯，很多人是恐惧的。同时驾驭两三灯，甚至五灯，的确是很难。但是如果仅仅只是一灯的话，问题就简单很多。更何况即便是，一人一灯 Long, flat curves are preferable at all times, as they are pleasing in appearance and decrease possibility of future obsolescence. Long, flat curves should be
11、used for small changes in direction, as short curves appear as kink. Also horizontal and vertical alignment must be considered together, not separately. For example, a sharp horizontal curve beginning near a crest can create a serious accident hazard.在任何时候都长且平坦的曲线都是优选，因为它们在外观上 令人愉悦并能减少将来报废的可能性。长，平面曲
12、线应该用 于在方向上的微小变化，如短的曲线显示为“扭结”。同时平面线形和纵断面线形必须一起考虑，而不是分开。例如，一 个锐的平曲线的开始接近高峰时可能会产生严重事故的危险 。obsolescence报废 crest高峰对于闪光灯，很多人是恐惧的。同时驾驭两三灯，甚至五灯，的确是很难。但是如果仅仅只是一灯的话，问题就简单很多。更何况即便是，一人一灯A vehicle traveling in a curved path is subject to centrifugal force. This is balanced by an equal and opposite force develope
13、d through superelevation and side friction. From a highway design standpoint, both superelevation and side friction cannot exceed certain maximums, and these controls place limits on the sharpness of curves that can be used with a design speed. 车辆在弯曲道路行驶受到离心力。这个平衡通过大小相等方向相反的超高和侧向摩擦力来达到。从公路设计的观点来 讲，超
14、高和侧向摩擦力都不能超过某个最大值，这些控制值 设置了曲线锐度限值，曲线锐度限值可以与设计速度建立联 系。vehicle 车辆 centrifugal force离心力 superelevation超高 side friction侧向摩擦力对于闪光灯，很多人是恐惧的。同时驾驭两三灯，甚至五灯，的确是很难。但是如果仅仅只是一灯的话，问题就简单很多。更何况即便是，一人一灯When roads intersect or a railroad spans across a road, the road intersections are needed. The intersection can be
15、at-grade intersection and grade-separated junction. The freeways only adopt the latter intersection. The typical at-grade crossings are cross roads, T intersection, and rotary intersection, as shown in following Fig. 27-3. 当相交的道路或铁路横跨道路时，需要设置道路交叉口。 交叉口可以是平面交叉的和立 体交叉。该高速公路仅采用后 者的交叉口。典型的平面交叉 口的十字路口，T形
16、交叉，及 环形交叉，如图下所示 27-3。intersect 交叉 junction 连接 rotary 环形对于闪光灯，很多人是恐惧的。同时驾驭两三灯，甚至五灯，的确是很难。但是如果仅仅只是一灯的话，问题就简单很多。更何况即便是，一人一灯 Clover-leaf Interchange Diamond InterchangeGrade-separated junctions Rotary Interchange Trumpet Interchange苜蓿叶 菱形 环形 喇叭形 立体交叉口对于闪光灯，很多人是恐惧的。同时驾驭两三灯，甚至五灯，的确是很难。但是如果仅仅只是一灯的话，问题就简单很多。更何况即便是，一人一灯高速公路普通公路与高速公路的转弯线形的比较对于闪光灯，很多人是恐惧的。同时驾驭两三灯，甚至五灯，的确是很难。但是如果仅仅只是一灯的话，问题就简单很多。更何况即便是，一人一灯When roads intersect or a railroad spans across a ro
