公路幾何設(shè)計(jì)外文翻譯

1、<p><b>　　公路幾何設(shè)計(jì)</b></p><p><b>　　A 路線設(shè)計(jì)</b></p><p>　　道路的線形反映在平面圖上是由一系列的直線和與直線相連的圓曲線構(gòu)成的?，F(xiàn)代設(shè)計(jì)時(shí)常在直線與圓曲線之間插入緩和曲線。</p><p>　　線形應(yīng)是連續(xù)的，應(yīng)避免平緩線形到小半徑曲線的突變或者長(zhǎng)直線末端與小半

2、徑曲線相連接的突然變化，否則會(huì)發(fā)生交通事故。同樣，不同半徑的圓弧首尾相接（曲線）或在兩半徑不同的圓弧之間插入短直線都是不良的線形。除非在圓弧之間插入緩和曲線。長(zhǎng)而平緩的曲線總是良好的線形，因?yàn)檫@種曲線線形優(yōu)美，將來(lái)也不會(huì)廢棄。然而，雙向道路線形全由曲線構(gòu)成也是不理想的，因?yàn)橐恍{駛員通過(guò)曲線路段時(shí)總是猶豫。長(zhǎng)而緩的曲線應(yīng)用在拐角較小的地方。如果采用短曲線，則會(huì)出現(xiàn)“扭結(jié)”。另外，線路的平、縱斷面設(shè)計(jì)應(yīng)綜合考慮，而不應(yīng)只顧其一，不顧其二，

3、例如，當(dāng)平曲線的起點(diǎn)位于豎曲線的頂點(diǎn)附近時(shí)將會(huì)產(chǎn)生嚴(yán)重的交通事故。</p><p>　　行駛在曲線路段上的車輛受到離心力和作用，就需要一個(gè)大小相同方向相反的由超高和側(cè)向磨擦提供的力抵消它，從公路設(shè)計(jì)的角度看，超高或橫向摩擦力都不能超過(guò)某一最大值，這些控制值對(duì)于某一規(guī)定設(shè)計(jì)車速可能采用曲線的曲率作了限制。通常情況下，某一圓曲線的曲率是由其半徑來(lái)體現(xiàn)的。而對(duì)于線形設(shè)計(jì)而言，曲率常常通過(guò)曲度來(lái)描述，即100ft長(zhǎng)的曲線

4、所對(duì)應(yīng)的中心角，曲度與曲線的半徑成反比。</p><p>　　公路的直線地段設(shè)置正常的路拱，而曲線地段則設(shè)置超高，在正常斷面與超高斷面之間必須設(shè)置過(guò)渡漸變路須。通常的做法是維持道路每一條中線設(shè)計(jì)標(biāo)高不變，通過(guò)抬高外側(cè)邊緣，降低內(nèi)側(cè)邊緣以形成超高，對(duì)于直線與圓曲線直接相連的線形，超高應(yīng)從未到達(dá)曲線之前的直線上開(kāi)始，在曲線頂點(diǎn)另一端一定距離以外達(dá)到全部超高。</p><p>　　如果車輛以高速

5、度行駛在一段受限制的路段，如直線與小半徑的圓曲線相連，行車會(huì)極不舒服。汽車駛近曲線路段時(shí)，超高開(kāi)始，車輛向內(nèi)側(cè)傾斜，但乘客須維持身體的垂直狀態(tài)，因?yàn)榇藭r(shí)未受到離心力的作用。當(dāng)汽車到達(dá)曲線路段時(shí)，離心力突然產(chǎn)生，迫使乘客向外傾斜，為了維持平衡，乘客必須迫使自己的身體向內(nèi)側(cè)傾斜。由于剩余超高發(fā)揮作用，乘客須作進(jìn)一步的姿勢(shì)高干中。當(dāng)汽車離開(kāi)曲線時(shí)，上述過(guò)程剛好相反。插入緩和曲線后，半徑從無(wú)窮大逐漸過(guò)渡到圓曲線上的某一固定值，離心力逐漸增大，沿

6、緩和曲線心設(shè)置超高，離心力平穩(wěn)逐漸增加，避免了行車顛簸。</p><p>　　緩和曲線在鐵路上已經(jīng)使用多年，但在公路上最近才得以應(yīng)用，這可以理解?；疖嚤仨氉裱_的運(yùn)行軌道，采用緩和曲線后，上述那種不舒服的感覺(jué)才能消除。然而，汽車司機(jī)在公路上可以隨意改變側(cè)向位置，通過(guò)迂迴進(jìn)入圓曲線來(lái)為自己提供緩和曲線。但是在一個(gè)車道上（有時(shí)在其他車道上）做這種迂迴行駛是非常危險(xiǎn)的。設(shè)計(jì)合理的緩和曲線使得上述迂迴沒(méi)有必要。多從安全

7、為計(jì)，公路部門廣泛采用了緩和曲線。</p><p>　　對(duì)于半徑相同的圓曲線來(lái)說(shuō)，在未端加上緩和曲線就會(huì)改變曲線與直線的相關(guān)位置，因此應(yīng)在最終定線勘測(cè)之前應(yīng)決定是否采用緩和曲線。一般曲線的起點(diǎn)標(biāo)為PC或BC，終點(diǎn)標(biāo)為PT或EC。對(duì)含有緩和曲線的曲線，通常的標(biāo)記配置增為：TC、SC、CS和ST。對(duì)于雙向道路，急彎處應(yīng)增加路面寬度，這主要基于以下因素：（1）駕駛員害怕駛出路面邊緣；（2）由于車輛前輪和后輪的行駛軌跡不

8、同，車輛有效橫向?qū)挾燃哟?；?）車輛前方相對(duì)于公路中線傾斜而增加的寬度。對(duì)于寬度為24ft的道路，增加的寬度很小，可以忽略。只有當(dāng)設(shè)計(jì)車速為30mile/h，且曲度大于22℃時(shí)，加寬可達(dá)2ft。然而，對(duì)于較窄的路面，即使是在較平緩的曲線路段上，加寬也是很重要推薦加寬值及加寬設(shè)計(jì)見(jiàn)《公路線形設(shè)計(jì)》</p><p><b>　　B縱坡線</b></p><p>　　公路的

9、豎向線形及其對(duì)車輛運(yùn)行的安全性和經(jīng)濟(jì)性的影響構(gòu)成了公路設(shè)計(jì)中最重要的要素之一。豎向線形由直線和豎向拋物線或圓曲線組成，稱為縱坡線?？v坡線從水平線逐漸上升時(shí)稱為坡度變化的影響。</p><p>　　在確定坡度時(shí)最理想的情況是挖方與填方平衡，沒(méi)有大量的借方或棄方。所有運(yùn)土都盡可能下坡運(yùn)并且距離不長(zhǎng)，坡度應(yīng)隨地形而變，并且與既有排水系統(tǒng)的升、降方向一致。在山區(qū)，坡度要使得挖填平衡以使總成本最低。在平原或草原地區(qū)，坡度與

10、地表近似平行，介是高于地表足夠的高度，以利于路面排水，苦有必要，可利用風(fēng)力來(lái)清除表面積雪。如公路接近或沿河流走行，縱坡線的高度由預(yù)期洪水位來(lái)決定。無(wú)論在何種情況下，平緩連續(xù)的坡度線要比由短直線段連接短豎曲線構(gòu)成的不斷變向的坡度線好得多。</p><p>　　由上坡向下坡變化的路段應(yīng)設(shè)在挖方路段，而由下坡向上坡變化的路段應(yīng)設(shè)在填方路段，這樣的線形設(shè)計(jì)較好，往往可以避免形成與現(xiàn)狀地貌相反的圭堆或是凹地。與挖填方平衡相

11、比，在確定縱坡線時(shí)，其他考慮則重要得多。</p><p>　　城市項(xiàng)目往往比農(nóng)村項(xiàng)目要求對(duì)控制要素進(jìn)行更詳盡的研究，對(duì)高程進(jìn)行更細(xì)致地調(diào)整。一般來(lái)說(shuō)，設(shè)計(jì)與現(xiàn)有條件相符的坡度較好，這樣可避免一些不必要的花費(fèi)。</p><p>　　在坡度的分析和控制中，坡度對(duì)機(jī)動(dòng)車運(yùn)行費(fèi)用的影響是最重要的考慮因素之一。坡度增大油耗顯然增大，車速就要減慢。一個(gè)較為經(jīng)濟(jì)的方案則可使坡度減小而增加的年度成本與坡度

12、不減而增加的車輛運(yùn)行年度成本之間相平衡。這個(gè)問(wèn)題的準(zhǔn)確方法取決于對(duì)交通流量和交通類型的了解，這只有通過(guò)交通調(diào)查方能獲知。</p><p>　　在不同的州，最大縱坡也相差懸殊，AASHTO建議由設(shè)計(jì)車速和地形來(lái)選擇最大縱坡。現(xiàn)行設(shè)計(jì)以設(shè)計(jì)車速為70mile/h時(shí)最大縱坡為5%，設(shè)計(jì)車速30mile/h時(shí)，根據(jù)地形不同，最大縱坡一般為7％－12％。</p><p>　　當(dāng)采用較長(zhǎng)的待續(xù)爬坡時(shí)，

13、在沒(méi)有為慢行車輛提供爬坡道時(shí)，坡長(zhǎng)不能夠超過(guò)臨界坡長(zhǎng)。臨界坡長(zhǎng)可從3％縱坡的1700ft變化至8%縱坡的500ft。</p><p>　　持續(xù)長(zhǎng)坡的坡度必須小于公路任何一個(gè)斷面的最大坡度，通常將長(zhǎng)的持續(xù)單一縱坡斷開(kāi)，設(shè)計(jì)成底部為一陡坡，而接近坡頂則讓坡度減小。同時(shí)還要避免由于斷面傾斜而造成的視野受阻。調(diào)整公路的最大縱坡為9%只有當(dāng)路面排水成問(wèn)題時(shí)，如水必須排至邊溝或排水溝，最小坡度標(biāo)準(zhǔn)才顯示其重要性。這種情況下，

14、AASHTO建議最小坡度為0.35%。</p><p><b>　　C視距</b></p><p>　　為保證行車安全，公路設(shè)計(jì)必須使得駕駛員視線前方有足夠的一段距離，使他們能夠避讓意外的障礙物，或者安全地超車。視距就是車輛駕駛員前方可見(jiàn)的公路長(zhǎng)度。安全視距具有兩方面含義：“停車視距”或“不超車視距”或“超車視距”。</p><p>　　有時(shí)，

15、大件物體也許會(huì)掉到路上，會(huì)對(duì)撞上去的車輛造成嚴(yán)重的危害。同樣，轎車或卡車也可能會(huì)被一溜車輛阻在車道上。無(wú)論是哪種情況發(fā)生，合理設(shè)計(jì)要求駕駛員在一段距離以外就能看見(jiàn)這種險(xiǎn)情，并在撞上去之前把車剎住。此外，認(rèn)為車輛通過(guò)離開(kāi)所行駛的車道就可以躲避危險(xiǎn)的想法是不安全的，因?yàn)檫@會(huì)導(dǎo)致車輛失控或與另一輛車相撞。</p><p>　　停車視距由峽谷部分組成：第一部分是當(dāng)駕駛員發(fā)現(xiàn)障礙物面作出制動(dòng)之前駛過(guò)的一段距離，在這一察覺(jué)與

16、反應(yīng)階段，車輛以其初始速度行駛；第二部分是駕駛員剎車后車輛所駛過(guò)的一段距離。第一部分停車視距取決于車速及駕駛員的察覺(jué)時(shí)間和制動(dòng)時(shí)間。第二部分停車視距取決于車速、剎車、輪胎、路面的條件以及公路的線形的坡度。</p><p>　　在雙車道公路上，每間隔一定距離，就應(yīng)該提供超越慢行車輛的機(jī)會(huì)。否則，公路容量將降低，事故將增多，因?yàn)榧痹锏鸟{駛員在不能安全超車時(shí)冒著撞車危險(xiǎn)強(qiáng)行超車，能被看清的允許安全超車的前方最小距離叫做

17、超車視距。</p><p>　　駕駛員在做出是否超車的決定時(shí)，必須將前方的能見(jiàn)距離與完成超車動(dòng)作所需的距離對(duì)比考慮。影響他做出決定的因素是開(kāi)車的小心程度和車輛加速性能。由于人與人的顯著差別，主要是人的判斷和動(dòng)作而不是力學(xué)定理決定的超車行為隨著駕駛員的不同而大不相同。為了確立超車視距值，工程人員觀察了許多駕駛員的超車行為。在1938～1941年間，進(jìn)行了建立超車視距標(biāo)準(zhǔn)的基本調(diào)查。假設(shè)操作條件如下：</p&g

18、t;<p><b>　　被超車輛勻速行駛</b></p><p>　　超車在進(jìn)入超車區(qū)時(shí)減速行駛在被超車后。</p><p>　　當(dāng)?shù)竭^(guò)超車區(qū)時(shí)，駕駛員需一短時(shí)間來(lái)觀察超車區(qū)，并開(kāi)始超車。</p><p>　　面對(duì)相向車輛，在一個(gè)延遲的啟動(dòng)和一個(gè)匆忙的拐彎的動(dòng)作中，完成超車。在超車過(guò)程中，超車在超車道上加速，其平均速度比被超車快1

19、0mile/h。</p><p>　　當(dāng)超車返回到它原來(lái)的車道上時(shí)，在它與另一車道上的相向車輛之間必須有一定的安全距離。</p><p>　　以上五項(xiàng)之和就是超車視距。</p><p>　　Geometric Design of Highways</p><p>　　A Alignment Design</p><p&

20、gt;　　The alignment of a road is shown on the plane view and is a series of straight lines called tangents connected by circular. In modern practice it is common to interpose transition or spiral curves between tangents a

21、nd circular curves.</p><p>　　Alignment must be consistent. Sudden changes from flat to sharp curves and long tangents followed by sharp curves must be avoided; otherwise, accident hazards will be created. Li

22、kewise, 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. Long, flat curves are p

23、referable at all times, as they are pleasing in appearance and decrease possibility of future obsolesc</p><p>　　A vehicle traveling in a curved path is subject to centrifugal force. This is balanced by an eq

24、ual and opposite force developed through cannot exceed certain maximums, and these controls place limits on the sharpness of curves that can be used with a design speed.</p><p>　　Usually the sharpness of a g

25、iven circular curve is indicated by its radius. However, for alignment design, sharpness is commonly expressed in terms of degree of curve, which is the central angle subtended by a 100-ft length of curve. Degree of curv

26、e is inversely proportional to the radius.</p><p>　　Tangent sections of highways carry normal cross slope; curved sections are superelevated. Provision must be made for gradual change from one to the other.

27、This usually involves maintaining the center line of each individual roadway at profile grade while raising the outer edge and lowering the inner edge to produce the desired superelevation is attained some distance beyon

28、d the point of curve. </p><p>　　If a vehicle travels at high speed on a carefully restricted path made up of tangents connected by sharp circular curve, riding is extremely uncomfortable. As the car approach

29、es a curve, superelevation begins and the vehicle is tilted inward, but the passenger must remain vertical since there is on centrifugal force requiring compensation. When the vehicle reaches the curve, full centrifugal

30、force develops at once, and pulls the rider outward from his vertical position. To achieve a position of </p><p>　　Easement curves have been used by the railroads for many years, but their adoption by highwa

31、y agencies has come only recently. This is understandable. Railroad trains must follow the precise alignment of the tracks, and the discomfort described here can be avoided only by adopting easement curves. On the other

32、hand, the motor-vehicle operator is free to alter his lateral position on the road and can provide his own easement curves by steering into circular curves gradually. However, this weaving</p><p>　　For the s

33、ame radius circular curve, the addition of easement curves at the ends changes the location of the curve with relation to its tangents; hence the decision regarding their use should be made before the final location surv

34、ey. They point of beginning of an ordinary circular curve is usually labeled the PC (point of curve) or BC (beginning of curve). Its end is marked the PT (point of tangent) or EC (end of curve). For curves that include e

35、asements, the common notation is, as stationing inc</p><p>　　On two-lane pavements provision of a wilder roadway is advisable on sharp curves. This will allow for such factors as (1) the tendency for drivers

36、 to shy away from the pavement edge, (2) increased effective transverse vehicle width because the front and rear wheels do not track, and (3) added width because of the slanted position of the front of the vehicle to the

37、 roadway centerline. For 24-ft roadways, the added width is so small that it can be neglected. Only for 30mph design speeds and curves</p><p><b>　　B Grades</b></p><p>　　The vertical

38、 alignment of the roadway and its effect on the safe and economical operation of the motor vehicle constitute one of the most important features of road design. The vertical alignment, which consists of a series of strai

39、ght lines connected by vertical parabolic or circular curves, is known as the “grade line.” When the grade line is increasing from the horizontal it is known as a “plus grade,” and when it is decreasing from the horizont

40、al it is known as a “minus grade.” In analyzing </p><p>　　In the establishment of a grade, an ideal situation is one in which the cut is balanced against the fill without a great deal of borrow or an excess

41、of cut to be wasted. All hauls should be downhill if possible and not too long. The grade should follow the general terrain and rise and fall in the direction of the existing drainage. In mountainous country the grade ma

42、y be set to balance excavation against embankment as a clue toward least overall cost. In flat or prairie country it will be approx</p><p>　　Changes of grade from plus to minus should be placed in cuts, and

43、changes from a minus grade to a plus grade should be placed in fills. This will generally give a good design, and many times it will avoid the appearance of building hills and producing depressions contrary to the genera

44、l existing contours of the land. Other considerations for determining the grade line may be of more importance than the balancing of cuts and fills.</p><p>　　Urban projects usually require a more detailed st

45、udy of the controls and finer adjustment of elevations than do rural projects. It is often best to adjust the grade to meet existing conditions because of the additional expense of doing otherwise.</p><p>　　

46、In the analysis of grade and grade control, one of the most important considerations is the effect of grades on the operating costs of the motor vehicle. An increase in gasoline consumption and a reduction in speed are a

47、pparent when grades are increase in gasoline consumption and a reduction in speed is apparent when grades are increased. An economical approach would be to balance the added annual cost of grade reduction against the add

48、ed annual cost of vehicle operation without grade reduction.</p><p>　　While maximum grades vary a great deal in various states, AASHTO recommendations make maximum grades dependent on design speed and topogr

49、aphy. Present practice limits grades to 5 percent of a design speed of 70 mph. For a design speed of 30 mph, maximum grades typically range from 7 to 12 percent, depending on topography.</p><p>　　Wherever lo

50、ng sustained grades are used, the designer should not substantially exceed the critical length of grade without the provision of climbing lanes for slow-moving vehicles. Critical grade lengths vary from 1700 ft for a 3 p

51、ercent grade to 500 ft for an 8 percent grade.</p><p>　　Long sustained grades should be less than the maximum grade on any particular section of a highway. It is often preferred to break the long sustained u

52、niform grade by placing steeper grades at the bottom and lightening the grade near the top of the ascent. Dips in the profile grade in which vehicles may be hidden from view should also be avoided.</p><p>　　

53、Maximum grade for highway is 9 percent. Standards setting minimum grades are of importance only when surface drainage is a problem as when water must be carried away in a gutter or roadside ditch. In such instances the A

54、ASHTO suggests a minimum of 0.35%.</p><p>　　C Sight Distance</p><p>　　For safe vehicle operation, highway must be designed to give drivers a sufficient distance or clear version ahead so that t

55、hey can avoid unexpected obstacles and can pass slower vehicles without danger. Sight distance is the length of highway visible ahead to the driver of a vehicle. The concept of safe sight distance has two facets: “stoppi

56、ng” (or “no passing”) and “passing”.</p><p>　　At times large objects may drop into a roadway and will do serious damage to a motor vehicle that strikes them. Again a car or truck may be forced to stop in the

57、 traffic lane in the path of following vehicles. In dither instance, proper design requires that such hazards become visible at distances great enough that drivers can stop before hitting them. Further more, it is unsafe

58、 to assume that one oncoming vehicle may avoid trouble by leaving the lane in which it is traveling, for this might res</p><p>　　Stopping sight distance is made up of two elements. The first is the distance

59、traveled after the obstruction comes into view but before the driver applies his brakes. During this period of perception and reaction, the vehicle travels at its initial velocity. The second distance is consumed while t

60、he driver brakes the vehicle to a stop. The first of these two distances is dependent on the speed of the vehicle and the perception time and brake-reaction time of the operator. The second distance dep</p><p&

61、gt;　　On two-lane highways, opportunity to pass slow-moving vehicles must be provided at intervals. Otherwise capacity decreases and accidents increase as impatient drivers risk head-on collisions by passing when it is un

62、safe to do so. The minimum distance ahead that must be clear to permit safe passing is called the passing sight distance.</p><p>　　In deciding whether or not to pass another vehicle, the driver must weigh th

63、e clear distance available to him against the distance required to carry out the sequence of events that make up the passing maneuver. Among the factors that will influence his decision are the degree of caution that he

64、exercises and the accelerating ability of his vehicle. Because humans differ markedly, passing practices, which depend largely on human judgment and behavior rather than on the laws of mechanics, vary con</p><

65、p>　　The overtaken vehicle travels at a uniform speed.</p><p>　　The passing vehicle has reduced speed and trails the overtaken one as it enters the passing section.</p><p>　　When the passing s

66、ection is reached, the driver requires a short period of time to perceive the clear passing section and to react to start his maneuver.</p><p>　　Passing is accomplished under what may be termed a delayed sta

67、rt and a hurried return in the face of opposing traffic. The passing vehicle accelerates during the maneuver and its average speed during occupancy of the left lane is 10 mph higher than that of the overtaken vehicle.<

68、;/p><p>　　When the passing vehicle returns to its lane there is a suitable clearance length between it and an oncoming vehicle in the other lane.</p><p>　　The five distances, in sum, make up passin