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1、精选优质文档-倾情为你奉上Design of the Alignment线形设计 The alignment of a highway is composed of vertical and horizontal elements. The vertical alignment includes straight (tangent) highway grades and the parabolic curves that connect these grades. The horizontal alignment includes the straight (tangent) sections
2、 of the roadway and the circular curves that connect their change in direction. 公路线形包括平曲线和竖曲线元素。竖曲线包括直坡线（切线）和连接这些直坡线的抛物线。平曲线包括公路的直线部分（切线）和连接两直线并转向的圆曲线。 The design of the alignment depends primarily on the design speed selected for the highway. The least costly alignment is one that generally takes t
3、he form of the natural topography. It is not always possible to select the lowest cost alternative because the designer has to adhere to certain standards that may not exist on the natural topography. 线形的设计取决于公路的设计速度。最经济的线形是沿着自然地形展线。现实中设计师往往不能选择造价最低的方案，因为他们必须遵循特定的技术标准，而这些标准在自然地形中也许难以达到。 It is import
4、ant that the alignment of a given section has consistent standards to avoid sudden changes in the vertical and horizontal layout of the highway. It is also important that both horizontal and vertical alignments be designed to complement each other, since this will result in a safer and more attracti
5、ve highway. 重要的是给定部分的线形必须符合规范来避免公路在水平和竖直布局上产生突变。同样重要的是设计的平曲线和竖曲线要相互协调，因为这样才能设计出安全并更有吸引力的公路。 One factor that should be considered to achieve compatibility is the proper balancing of the grades of tangents with curvatures of horizontal curves and the location of horizontal and vertical curves with res
6、pect to each other. For example, a design that achieves horizontal curves with large radii at the expense of steep or long grades is a poor design. Similarly, if sharp horizontal curves are placed at or near the top of pronounced crest vertical curves or at or near the bottom of a pronounced sag ver
7、tical curve, a hazardous condition will be created at these sections of the highway. Thus, it is important that coordination of the vertical and horizontal alignments be considered at the early stages of preliminary design. 为提高协调性应考虑的因素之一是保持直线坡度和曲线曲率均衡，处理好平曲线和竖曲线之间的相互位置。例如，大半径平曲线搭配长陡纵坡是一种较差的设计。同样，如果
8、在凸形竖曲线的顶部及附近或在凹形竖曲线底部及附近设置小半径平曲线，那该路段就会变得很危险。因此，在初步设计阶段综合考虑平纵曲线很重要。 The vertical alignment of a highway consists of straight sections known as grades, or tangents, connected by vertical curves. The design of the vertical alignment therefore involves the selection of suitable grades for the tangent s
9、ections and the appropriate length of the vertical curves. The topography of the area through which the road traverses has a significant impact on the design of the vertical alignment. 公路竖曲线由纵坡线或称切线以及连接他们的竖曲线组成。因而，竖曲线的设计包括直线合适坡度的选择和竖曲线合适长度的设计。路线所穿越地区的地形对竖曲线的设计有十分重要的影响。 The effect of grade on the per
10、formance of heavy vehicles must be considered. The speed of a heavy vehicle can be significantly reduced if the grade is steep and/or long. Note that steep grades not only affect the performance of heavy vehicles but also the performance of passenger cars. In order to limit the effect of grades on v
11、ehicular operation, the maximum grade on any highway should be selected judiciously. 必须考虑到纵坡对重载交通的影响。如果纵坡很陡且/或很长，重交通车辆的车速将极大地降低。注意到坡度不仅影响重车的性能同时也影响轿车的性能。为限制纵坡对车辆运行的影响，任何公路都应恰当的选择最大坡度。 The selection of maximum grades for a highway depends on the design speed and the design vehicle. It is generally ac
12、cepted that grades of 4 to 5 percent have little or no effect on passenger cars, except for those with high weight/horsepower ratios, such as those found in compact and subcompact cars. As the grade increases above 5 percent, however, speeds of passenger cars decrease on upgrades and increase on dow
13、ngrades. 公路最大坡度的选择取决于设计速度和设计车辆。普遍认为4%-5%的坡度对客车的影响不大或没有影响，除非是（质量/功率）较高的车，例如那些小型车或微型车。然而，当坡度大于5%时，客车上坡速度进一步降低，下坡速度进一步增加。 Grade has a greater impact on trucks than passenger cars. Extensive studies have been conducted, and results have shown that truck speed may increase up to 5 percent on downgraded a
14、nd decrease by 7 percent on upgrades, depending on the percent and length of the grade. 坡度对卡车的影响大于客车。进行了广泛研究，其结果表明卡车下坡时速度增加超过5%，上坡时速度降低超过7%，取决于坡度和坡长。 Maximum grades have been established, based cm the operating characteristics of the design vehicle on the highway. These vary from 5 percent for a des
15、ign speed of 70mi/h to between 7 and 12 percent for a design speed of 30 mi/h, depending on the type of highway. Note that the recommended maximum grades should not be used frequently, particularly when grades are long and the traffic includes a high percentage of trucks. On the other hand, when gra
16、de lengths are less than 500 ft and roads are one-way in the downgrade direction, maximum grades may be increased by up to 2 percent, particularly on low-volume rural highways. 最大坡度根据设计时就已确定的公路上汽车操控特点确定。按公路类型不同，最大坡度从设计速度70英里/小时的5%到设计速度30英里/小时的7%-12%不等。注意到推荐最大坡度不能频繁使用，尤其是纵坡较长而且车辆中卡车百分比较大时。另一方面，当坡长不足5
17、00英尺而且是下坡路段单行道时，最大纵坡可以增加超过2%，尤其在交通量小的乡村公路。 Minimum grades depend on the drainage conditions of the highway. Zero-percent grades may be used on uncurbed pavements with adequate cross slopes to laterally drain the surface water. When pavements are curbed, however, a longitudinal grade should be provid
18、ed to facilitate the longitudinal flow of the surface water. It is customary to use a minimum of 0. 5 percent in such cases, although this may be reduced to 0.3 percent on high-type pavement constructed on suitably crowned, firm ground. 最小坡度取决于公路排水条件。零坡可以用于不受限的有适当路拱横坡来排干路表水的路面。然而，当路面受限制时，纵坡应能促进路表水的纵
19、向流动。这种情况下通常采用0.5%的最小纵坡，而在有合适铺装、周围硬化的高等级路面中可能减至0.3%。 Vertical curves are used to provide a gradual change from one tangent grade to another so that vehicles may run smoothly as they traverse the highway. These curves are usually parabolic in shape. The expressions developed for minimum lengths of ver
20、tical curves are therefore based on the properties of a parabola. They are classified as crest vertical curves or sag vertical curves. 竖曲线通常用来使路线从一个坡度到另一个坡度的平缓过渡，这样在车辆穿越公路的时候可以平顺地行驶。这些曲线通常是抛物线形的。竖曲线最小长度公式取决于抛物线的性质。竖曲线又分为凹形竖曲线和凸形竖曲线。 The main criteria used for designing vertical curves are: (1) provi
21、sion of minimum stopping sight distance;(2) adequate drainage; (3) comfortable in operation; (4) pleasant appearance. The first criterion is the only criterion associated with crest vertical curves, whereas all four criteria are associated with sag vertical curves. 设计竖曲线的主要标准包括：（1）停车视距的要求；（2）充分考虑排水要
22、求；（3）行车舒适性要求；（4）路线美观要求。凸形竖曲线只与第一个条件有关，而凹形竖曲线与四个条件都有关。 The horizontal alignment consists of straight sections of the road (known as tangents) connected by horizontal curves. The curves are usually segments of circles, which have radii that will provide for a smooth flow of traffic. The design of the
23、horizontal alignment entails the determination of the minimum radius, the determination of the length of the curve, and the computation of the horizontal offsets from the tangents to the curve to facilitate locating the curve in the field. In some cases, to avoid a sudden change from a tangent with
24、infinite radius to a curve of finite radius, a curve with radii varying from infinite to the radius of the circular curve is placed between the circular curve and the tangent. Such a curve is known as a spiral or transition curve. There are four types of horizontal curves: simple, compound, reversed
25、, and spiral. 平面线形由公路的直线部分和连接它的平曲线组成。平曲线通常是圆曲线段组成的，圆曲线有一定半径可以使车流平顺通过。因此，平面线形的设计需要确定最小半径、曲线长度以及从切线到曲线的平面支距，以利于曲线实地定线。有时，为了避免从直线曲率无限大到曲线有限曲率的突变，人们在圆曲线和直线间插入一段曲率从无限大到圆曲线曲率逐渐变化的曲线。这种曲线叫做螺旋曲线或缓和曲线。有四种类型的平曲线：单曲线、复曲线、反向曲线、螺旋曲线。 A sample curve is a segment of a circle while compound curves consist of two or
26、 more curves in succession, turning in the same direction, with any two successive curves having a common tangent point. These curves are mainly used to obtain desirable shapes of the horizontal alignment, particularly for at-grade intersections, ramps of interchanges, and highway sections in diffic
27、ult topographic areas. To avoid abrupt changes in me alignment, the radii of any two consecutive simple curves that form a compound curve should not be widely different. AASHTO recommends that the ratio of the flatter radius to the sharper radius at intersections should not be greater than 2:1 so dr
28、ivers can adjust to sudden changes in curvature and speed. The maximum desirable ratio recommended for interchanges is 1.75:1, although 2:1 may be used. 单曲线由一段圆曲线组成，复曲线由两个或多个圆曲线连接而成，这些圆曲线转向相同且任何两相连圆曲线间有一个公切点。这些曲线主要用来获取较理想的平面线形，尤其在平面交叉、立体交叉和特殊地形路段。为避免线形突变，组成复曲线的两相连单曲线半径不应相差过大。AASHTO（美国国家公路与运输协会标准）规定，
29、平面交叉口交大半径与较小半径之比不得超过2:1，这样就可以让司机适应曲率和速度的突变。立体交叉比较理想的曲率比是1.75:1，然而2:1也在用。 To provide a smooth transition from a flat curve to a sharp curve, and to facilitate a reasonable deceleration rate on a series of curves of decreasing radii, the length of each curve should observe minimum length requirements.
30、 为使大曲率半径和小区率半径间实现平顺过渡、保证在一系列半径间小的圆曲线上的减速率，每个圆曲线的长度应满足最小长度的要求。 Reverse curves usually consist of two simple curves with equal radii turning in opposite directions with a common tangent. They are generally used to change the alignment of a highway. 反向曲线通常由两个有公切点的等半径反向单曲线组成反向曲线常用于改变公路线形。 Reverse curves
31、 are seldom recommended because sudden changes to the alignment may result in drivers finding it difficult to keep in their lanes. When it is necessary to reverse the alignment, a preferable design consists of two simple horizontal curves, separated by a sufficient length of tangent between them, to
32、 achieve full superelevation. Alternatively, the simple curves may be separated by an equivalent length of spiral. 反向曲线很少被推荐使用，因为线形的突变可能会使司机感觉很难按车道行驶。必须设置反向曲线时，合理的做法是两个单曲线，中间插入一段足够长的直线以便完成全超高布置。作为一种选择，单曲线可以被等长度的回旋线隔开。 Transition curves are placed between tangents and circular curves or between two a
33、djacent circular curves having substantially different radii. The use of transition curves provides a vehicle path that gradually increases or decreases the radial force as the vehicle enters or leaves a circular curve. If the transition curve is a spiral, the degree of curve between the tangent and
34、 the circular curve varies from zero at the tangent end to the degree of the circular curve at the curve end. When the transition is placed between two circular curves, the degree of curve varies from that of the first circular curve to that of the second circular curve. 缓和曲线设在直线和圆曲线或者两相邻不同直径圆曲线之间。缓和曲线的作用是在车辆驶入或驶出圆曲线时为其提供一条径向力逐渐增大或逐渐减小的车道。如果缓和曲线是螺旋线，切线和圆曲线间的曲率在直线端的零到曲线端的圆曲线曲率间变化。当缓和曲线设在两圆曲线之间时，缓和曲线曲率在第一个圆曲线曲率和第二个圆曲线曲率间变化。 专心-专注-专业