Route_alignment_new

Route_alignment_new - 7.1 Introduction 7-1 CHAPTER 7...

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Unformatted text preview: 7.1 Introduction 7-1 CHAPTER 7 Transportation Route Alignments 7.1 Introduction The famous Silk Road has been one of the best known ancient trade routes. This route consisted of many sections, links, and alternates. The Silk Road was built as a caravan route connecting China and Western Europe. The route was more than 6,000 kilometers long. First Egyptians, then Romans, and other westerners established trade relationships with China. Far East products (primarily silk, paper, and spices) were transported along this route for many centuries. Caravan rest areas were built at distances 30-40 km. from one another. In this way, it was possible to travel between two caravan stations in eight to ten hours on foot. The Silk Road, as well as many other ancient and modern roads have ben highly influenced by terrain, and they followed the most convenient path, i.e. the path of least resistance. Clearly, the ideal alignment would be a great circle from the point of origin to the point of destination . The most convenient path is usually that one that follows the natural alignment of the countryside. A route alignment represents a defined three-dimensional path. It is usual and convenient to present route alignments in two dimensions: horizontal and vertical alignments . Vertical alignment (also called profile grade line) is composed of a sequence of straight line profiles connected by vertical parabolic curves. In some cases the profile grade increases from a flat alignment. In some other cases, profile grade decreases from a flat alignment. A plus grade denotes the situation when profile grade is increasing from a flat alignment (Figure 7.1). The opposite situation is known as a minus grade (Figure 7.1). 7.1 Introduction 7-2 Figure 7.1 De f nition of Vertical Pro f les (Plus Grade and Minus Grade ). Grades are expressed in [%] or in [m/m]. Horizontal alignment represents projection of the alignment onto xy plane (Figure 7.2). Figure 7.2 Horizontal Alignment. The position of a specific point on a highway is traditionally determined using concept of stations . A datum point on a highway alignment is specified. This initial point is designated station 0 + 000.000. The positions of all other points on the highway are calculated by measuring corresponding distances on a horizontal plane along the highway from the initial point. Each station contains one kilometer of highway alignment distance. For example, the point on a highway located 2345.6 m from the previously specified point, is designated station 2 + 345.600. The station 3 + 465.800 corresponds to the highway point located 3465.8 meters from the initial point. +- G 2 G 1 Tangent Tangent Curve Curve G 1 G 2 x y z (0,0,0) Horizontal alignment L L xy 7.2 Vertical Alignment 7-3 Let us create along horizontal alignment the surface orthogonal to the plane. Let us also denote the distance measured along the horizontal alignment . When we stretch this surface, it becomes flat. We call it becomes flat....
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This note was uploaded on 12/31/2011 for the course CEE 3604 taught by Professor Katz during the Fall '08 term at Virginia Tech.

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Route_alignment_new - 7.1 Introduction 7-1 CHAPTER 7...

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