1、Text1 Background One definition of a visually attractive and unobtrusive highway is the degree to which the horizontal and vertical alignments of the route have been integrated into its surrounding natural and human environments1.This takes careful planning and design,as noted in the AASHTO Green Bo
2、ok:Coordination of horizontal alignment and profile should not be left to chance but should begin with preliminary design,during which adjustments can readily be made.The designer should-study long,continuous stretches of highway in both plan and profile and visualize the whole in three dimensions.T
3、his application of a holistic approach to highway design,where the road is integrated into its surroundings,separates the outstanding project from one that merely satisfies basic engineering design criteria.An excellent description of this holistic design process is contained in the publication Aest
4、hetics in Transportation,from which the following is excerpted:A general rule for designers is to achieve a“flowing”line,with a smooth and natural appearance in the land,and a sensuous,rhythmic continuity for the driver.This effect results from following the natural contours of the land,using gracef
5、ul and gradual horizontal and vertical transitions,and relating the alignment to permanent features such as rivers or mountains.Text2 Horizontal and Vertical Alignment Considerations The greatest opportunities for influencing the horizontal and vertical alignments of a highway occur during the plann
6、ing and preliminary engineering phases associated with a new-location facility.The designs of such facilities have the most dramatic effects on the natural and human environments through which they pass.The more typical design problem faced by todays highway engineers is the improvement of an existi
7、ng highway or street.In many instances,the basic alignments may have been established well over 100 years ago.Regardless,the same basic design principles with respect to horizontal and vertical alignments can,however,be applied to both new and existing facilities.Important points to consider regardi
8、ng horizontal and vertical alignments are that they should be consistent with the topography,preserve developed properties along the road,and incorporate community values2.The superior alignments are ones that follow the natural contours of the land and do not affect aesthetic,scenic,historic,and cu
9、ltural resources along the way.Construction costs may be reduced in many instances when less earthwork is needed,and resources and development are preserved.It is not always possible,however,to avoid having an impact on both the natural and human environments.Text That is why the superior alignments
10、 incorporate input received by the community through a participatory design process.When possible,the alignment should be designed to enhance attractive scenic views,such as rivers,rock formations,parks,historic sites,and outstanding buildings.The designation of certain highways as scenic byways rec
11、ognizes the importance of preserving such features along our Nations roadways.Equally important as the consideration of the horizontal alignment is that of the facilitys vertical alignment3.A number of factors influence the vertical alignment of a highway,including the following:(1)Natural terrain;(
12、2)Minimum stopping sight distance for the selected design speed;(3)The number of trucks and other heavy vehicles in the traffic stream;(4)The basic roadway cross-section;i.e.,two lanes versus multiple lanes;(5)Natural environmental factors,such as wetlands and historic,cultural,and community resourc
13、es.Text3 Combination of Horizontal and Vertical Alignment The interrelationship of horizontal and vertical alignment is best addressed in the route location and preliminary design phases of a project.At this stage,appropriate tradeoffs and balances between design speed and the character of the road-
14、traffic volume,topography,and existing development-can be made.A mistake often made by inexperienced engineers is designing the horizontal alignment first and then trying to superimpose the design onto a vertical profile.Because they must be complementary,horizontal and vertical geometries must be d
15、esigned concurrently.Uncoordinated horizontal and vertical geometries can ruin the best parts and accentuate the weak points of each element.Excellence in the combination of their designs increases efficiency,and safety,encourages uniform speed,and improves appearance-almost always without additiona
16、l cost.One tool to assist in coordinating horizontal and vertical geometries is the use of computer-aided design(CAD).CAD enables highway designers to quickly assess the interrelationships between horizontal and vertical alignment,particularly in areas of difficult terrain.Proper consideration of th
17、ese basic design considerations will help to ensure that both new-location facilities and improvements to existing highways fit harmoniously into their surroundings4.Text(1)Issues There are numerous examples around this country of excellence in integration of the horizontal and vertical alignments o
18、f highways into their surroundings.Unfortunately,here are also examples of new or widened highways that have scarred a rural landscape or disrupted an established community.While these past actions cannot easily or inexpensively be rectified,future problems can be avoided by applying the principles
19、outlined above and the creative approaches detailed below.(2)Avoiding Impact on Adjacent Natural and Human Environments Particularly during the era of Interstate construction from the 1950s to the 1980s,a number of instances of new highway construction had a devastating impact on communities and are
20、as of environmental sensitivity.It is readily acknowledged that there will be some degree of physical impact on the surroundings associated with the construction of any new location highway or major reconstruction or widening of an existing highway facility.However,from the perspective of horizontal
21、 and vertical alignment,much of this impact can and should be alleviated.Text(3)Solution Impact on the surrounding environment can be minimized by careful attention to detail during the route location and preliminary design phases and a willingness of all concerned parties to work together toward a
22、common goal.For example,minor adjustments to the originally proposed horizontal and vertical alignments(combined with the use of short sections of retaining wall)along the Lincoln Beach Parkway(U.S.Route 101)in Oregon eliminated the need to acquire any of the adjacent homes and businesses.Similarly,
23、a minor horizontal alignment shift at the beginning of the project allowed for the Hollister Bypass(SR 156)in San Benito County,CA,to avoid affecting a number of historic properties.The use of a“cut-and-cover”design,whereby the roadway is placed below the existing ground level and covered over with
24、a park,building,or other public space can help to avoid negative impact5.Lake Place Park in Duluth,MN and other public parks were the result of cut-and-cover tunnels that not only saved historic properties but also gave pedestrians improved access to Lake Superior.In many cases,there is a potential
25、for designing a divided highway with independent horizontal and vertical alignments for each direction of traffic.Text4 Coordination between Horizontal and Vertical Alignment When horizontal and vertical alignments are designed separately from one another,unnecessarily large cuts and fills may be re
26、quired,resulting in very dramatic and often visually undesirable changes to the natural landscape.Solution:One of the ways to ensure the most effective coordination of horizontal and vertical alignment is through the use of a multidisciplinary design team during the planning and engineering phases o
27、f a project.On such projects as 1-66 in Fairfax and Arlington Counties in Virginia,the combined expertise of landscape architects,urban designers,structural engineers,and historic preservationists,in addition to civil engineers and highway designers,has resulted in superior highway improvement proje
28、cts.The concept of using a multidisciplinary design team is not new;it was pioneered in the early 1900s during the planning and design of the Bronx River Parkway in Westchester County,NY.After a period of use primarily on large-scale or controversial projects,this approach has come back into more ge
29、neral application as a way to achieve community consensus.New Words and phrasesalignment n.（道路）线型，定线 horizontal alignment 平面线型 vertical alignment 纵断面线型 route n.路线；航线；通道 American Association of State Highway and Transportation Officials(AASHTO)美国国家公路与运输协会 profile n.纵断面；侧面；轮廓 preliminary design(phase)
30、初步设计（阶段）contour n.等高线；轮廓transition n.过渡；转变；转换 earthwork n.土方工程，挖土 terrain n.地形，地势；领域；地带sight distance 视距 stopping sight distance 停车视距 cross-section n.横断面；横截面 lane n.车道；航线；小巷 two lanes 双车道 multiple lanes 多车道tradeoff n.折衷方案；权衡New Words and phrasestopography n.地势；地形 superimpose vt.添加，附加；重叠；安装 geometry
31、n.几何（学）computer aided design（CAD）计算机辅助设计 widened highway 扩宽的公路 retaining wall 挡土墙，护壁；护岸 cut-and-cover 下挖加盖板 landscape n.景观，风景 v.美化景观 landscape architect 景观设计师 urban designer 城市规划设计师 structural engineer 土木工程师Notes1.One definition of a visually attractive and unobtrusive highway is the degree to which
32、 the horizontal and vertical alignments of the route have been integrated into its surrounding natural and human environments一条具有视觉诱导性和线性平顺性的公路，要使得平纵线形与周围人文地理环境相协调。2.Important points to consider regarding horizontal and vertical alignments are that they should be consistent with the topography,prese
33、rve developed properties along the road,and incorporate community values平曲线和竖曲线设计的关键是，要综合考虑实际地形、沿线的发展建设与社会经济价值。3.Equally important as the consideration of the horizontal alignment is that of the facilitys vertical alignment相对于路基工程设施的水平对齐，它的垂直对齐同样重要，都应该被考虑。4.Proper consideration of these basic design
34、 considerations will help to ensure that both new-location facilities and improvements to existing highways fit harmoniously into their surroundings对这些基本设计原则的适当考虑有助于使新建设施和改进后的原有公路和谐的融入它们的周边环境。Notes5.The use of a“cut-and-cover”design,whereby the roadway is placed below the existing ground level and c
35、overed over with a park,building,or other public space can help to avoid negative impact 采用“随挖随填法”设计，使得路线可以布置在已有地面高程以下，可以减少对覆盖在其上的公园、建筑物或者其他公共空间的不利影响。Exercise（Translate the following Chinese into English,or English into Chinese）1.A general rule for designers is to achieve a“flowing”line,with a smoot
36、h and natural appearance in the land,and a sensuous,rhythmic continuity for the driver.This effect results from following the natural contours of the land,using graceful and gradual horizontal and vertical transitions,and relating the alignment to perm anent features such as rivers or mountains.2.Th
37、e use of a“cut-and-cover”design,whereby the roadway is placed below the existing ground level and covered over with a park,building,or other public space can help to avoid negative impact.Lake Place Park in Duluth,MN and other public parks were the result of cut-and-cover tunnels that not only saved
38、 historic properties but also gave pedestrians improved access to Lake Superior.3.Coordination of horizontal alignment and profile should not be left to chance but should begin with preliminary design,during which adjustments can readily be made.The designer should-study long,continuous stretches of
39、 highway in both plan and profile and visualize the whole in three dimensions4.Explicit design shall comply with driving mechanical requirements,should also consider the drivers visual,psychological and physiological requirements,in order to improve vehicle safety,comfort and economy.5.In order to p
40、rovide the above advantages,it is necessary to know what thickness of pavement section will support the heaviest anticipated traffic loads without grossly over-designing the pavement.Exercise（Translate the following Chinese into English,or English into Chinese）6.遵循以设计路线确定公路等级、设计速度的原则，其设计路段的长度不宜过短，且线性指标技术应保持相对均衡。7.路面设计任务是确定路面等级，选择路面类型，进行结构组合设计，计算各结构层厚度及确定材料配合比，达到在不同季节和水文条件下承受各种车辆荷载时具有良好的稳定性和足够的强度。8.良好的平纵线形设计将有利于提高道路行车效率及安全性，保证均一的车速，并且不需要增加额外费用，就可以改善道路外观。9.路面设计根据行车作用下路面的力学特性，可将路面分为柔性与刚性两种。10.由于平纵线形是相互补充的，设计时必须保持同步，而不是割裂开来，有些没有经验的设计师常常是错误的先设计平面线形，然后再添加纵面线形。
