外文翻译---低流量农村公路的统一设计.docx

附录A 外文翻译A.1 原文CONSISTENCY IN DESIGN FOR LOW-VOLUMERURAL ROADS3By Clarkson H. Oglesby, H. M. ASCE (Reviewed by the Highway Division)ABSTRACT: The 2,000,000 miles of low-volume rural roads in the United States are different than the high-volume roads and should be designed differently. Traffic volumes on them are low, averaging about 110 vehicles/day or about one vehicle entering a given mile from both ends every three minutes during peak hours. This contrasts with one vehicle every four seconds at capacity. Geometries on many of these roads have not changed since they were built in the 1920s and 1930s. Today, road improvements should be based on designs that are consistent and safe, but economical, because needs are great and funds are scarce. Present-day design practices for high volume roads require that each of their features meet a stipulated design speed set by modern surfaces and vehicles. This practice does not fit the low-volume situation since, whenever possible, drivers will exceed any affordable design speed. They must be slowed down when situations warrant it. A consistent approach to design which realizes cheap but safe improvements to low-volume roads is proposed. It involves integrating geometric design and positive guidance approaches. Positive guidance employs striping, signing, and other devices and strategies to mobilize drivers senses so that they will drive sensibly. Selecting the less costly between geometry and positive guidance techniques will produce safer roads more cheaply.INTRODUCTIONThere are approximately 3,200,000 mile (5,100,000 km) of rural roads in the United States. A rough estimate places some 2,000,000 (3,000,000km) of these in a low-volume category; this commonly includes those with average daily traffic less than 400 vehicles/day in both directions. On most of these roads volumes are considerably lower. One estimate places this average at 110 vehicles/day or a possible 20 in the peak hour. This means one vehicle every three minutes entering a given mile from both ends. In contrast, a major two-lane road, operating at capacity, will carry possibly 1,800 vehicles/hour so that a vehicle will enter a given mile every four seconds or 90 times as often.The money available to those responsible for high-volume roads is on the order of ten times as great per mile as for low-volume roads. It follows that strategies for new construction, upgrading, or maintenance of low-volume rural roads will be entirely different than for higher-volume roads, if the very limited money available for these purposes is to be used wisely.Given the uniqueness of the low-volume road problem, it seems appropriate to examine and possibly redefine what is meant by consistency in design for them. This paper attempts that task by examining the following topics as it applies to them:1. The origin and current status of local rural roads.2. How consistency in present-day geometric standards for new construction or renovation of low-volume roads has developed.3. Factors that have impinged on design standards for low-volume rural roads.4. Conclusions.ORIGIN AND CURRENT STATUS OF LOCAL RURAL ROADSFor the purpose of this paper, local rural roads are those that provide access to and thereby support activities on rural lands. These include farming, ranching, recreation, and access to forests or other natural resources. This definition excludes those roads, once rural or near towns, that are now in suburbia.Relatively little mileage has been added to low-volume rural systems in the last 50 years. They were developed when the aim was to get the farmer out of the mud. They are often characterized by narrow roadways and rights-of-way. In the middle west and west, where much of the land had been laid out in sections one mile square, rights-of-way were 66 ft (20 m). This width was dedicated to land access along the edges of adjacent sections. In the eastern states, many rights-of-way were narrower, often 33 ft (10 m) or less. In rolling or mountainous country, tortuous alignments were fitted closely to the contour of the ground. Today these often restrict speeds to 30 mile/hr (48 km/h) or less.In these earlier years, travel was mainly in horse-drawn vehicle. Even in the 1930s, when the last of these land-access roads were being constructed, speeds were low because neither vehicles nor road surfacings permitted fast travel. For reasons such as these, the concept of design speed did not exist. Today, the performance of motor vehicles is far different and the sizes and weights of trucks have increased dramatically. Furthermore, for possibly two-thirds of this low-volume rural mileage, gravel or earth surfaces have been paved, surface treated, or otherwise made relatively smooth and free of corrugations or dust. Presently, then, drivers expect to travel at higher speeds and only slow down when forced to do so by intersections or restricted vertical or horizontal alignment. On higher volume roads, many of which have been successively improved, this slowing is seldom required. And when it is, elaborate measures are taken to alert drivers. But this matching of improvements with speed has been far less frequent on low-volume rural roads because money has been scarce. Of that available, more than two-thirds (in 1978) has gone to maintenance and other purposes, leaving little for new construction or betterment.It would be untrue and unfair to say that those responsible for low-volume rural roads have done nothing to overcome this mismatch between driver expectations regarding speed and the roads. Through strategies such as spot improvements and scrounging money from their budgets and higher governmental levels for rebuilding certain roads, they have done much. But the gap still remains large. This, of course, applies not only to road geometry, but to surfacings and bridges as well.How CONSISTENCY IN PRESENT-DAY GEOMETRIC STANDARDS FOR NEWCONSTRUCTION OR RENOVATION OF LOW VOLUME RURAL ROADSHAS DEVELOPEDAs noted, most of the need for and geometries of low-volume rural roads developed fifty or more years ago to fit specific situations. Unless altered by maintenance, betterment, reconstruction, or complete replacement, they have changed little since. At that time, main rural roads were built to meet the same conditions and their geometry was not an issue. For example, as late as 1940, a leading highway engineering text book, by T. R. Agg (1), devotes only 22 pages to the entire subject of geometric design. In it Agg stated that considerable latitude is allowable in adapting the design to the particular situation (which may be topographical, financial, or political) as long as the design does no violence to basic principles. Agg calls for the exercise of originality and good engineering judgmentthat does not necessarily follow stereotyped standards.It was at about this same time (1937) that AASHO (now AASHTO) created a Committee on Planning and Design Policies. Its aim was to incorporate, in practice, highway design features that would result in maximum safety and utility. From this effort, in the period 1938-1944, came seven policy statements on geometric design that were adopted by AASHO. These were consolidated without change in 1950 into a single volume, Policies on Geometric Highway Design (3). A reworking resulted in a 1954 document called A Policy on Geometric Design (4). This document, commonly called the Blue Book, was redone again and published in 1965 under the same title (5). In 1969, a publication applying more specifically to low-volume rural roads was issued (2). Since that time the appropriateness of these policies, which set standards for all aspects of geometric design, have been under almost continuous review and a comprehensive revision is under preparation.From the beginning, those responsible for developing standards for geometric design have been attempting to keep pace with changes in the characteristics of motor vehicles and the expectations of drivers. This has led to a substantial raising of design controls or features. FACTORS THAT HAVE IMPINGED ON GEOMETRIC STANDARDSFOR LOW-VOLUME RURAL ROADSIn tracing the development of geometric standards and their application over the years in terms of their impact on low-volume rural roads policies, several factors can be seen. These include the following:1. Low-volume road engineers or administrators have made few direct inputs into geometric standards. They have been developed by specialists in geometric design, most of them in the Federal Highway Administration. They were adopted after review by geometric-design specialists in the state highway agencies working through AASHTO. Because these agencies deal primarily with high-volume situations, it is claimed that their representatives are not sensitive to the low-volume road situation. For example, the standards for low-volume as well as those for high-volume roads were based on the design speed concept, which has been defined as The maximum safe speed that can be maintained over a specific section of highway when conditions are so favorable that the design features of the highway govern. This definition implies that only the reckless few among drivers will exceed the design speed anywhere along the road. But this is not the way drivers behave on low-volume rural roads. Rather, whenever possible, even on short stretches, they will accelerate to their fear level speed. This can well be 50 or 60 mph (80 or 96 km/h) on a road with a stipulated. design speed of 20 or 30 mph (32 or 48 km/h). The problem on such roads becomes one of slowing drivers down to safe speeds as they approach road sections over which they must travel slowly. It might be said that the low design speeds stipulated in the standards for certain low-volume roads provide justification and professional support for designers using less costly alternatives at specific locations so that scarce dollars can be spread over greater mileages. Otherwise the design speed concept has little meaning in the low-volume rural road situation.2. Standards, once adopted, can become a straitjacket that prevents low-volume road engineers from following Aggs recommendation from 1940 which, to repeat, was to allow considerable latitude in adapting the design to particular situations (topographical, financial, or political). This freedom began to disappear when higher-level agencies, because they controlled the money, could dictate design details. Low-volume road engineers sometimes partially overcame this difficulty by having two sets of standards. The more costly set is employed when money from higher-level agencies is involved. The less costly one, done with local funds, does not have a standard cross section, but calls for widening or other improvements at spot locations.A related issue is the influence of these rigid standards when injured motorists sue road agencies and their engineers for negligence when roads do not meet them. This is an important but unanswered question.3. There has been a widely held but unproved notion that by insisting that standards of geometric design be followed, accidents will be reduced. Unfortunately, given the large mileage on existing low-volume roads and scarce funds for improving their geometry, exercising this option is seldom possible. Rather, for low-volume roads, the view that The design is inadequate and appears dangerous so accidents happen must be replaced with the notion, if it seems dangerous, take advantage of driver fear and caution in appropriate ways and accidents wont happen.CONCLUSIONThis paper, which deals with consistency in design standards for lowvolume rural roads, has traced the development for low-volume rural roads, most of which came into being when the aim was to get the farmer out of the mud. It indicated how high geometric design standards, which came later, were developed by those concerned with high volume roads, but who dictated their use because they controlled the money. It challenged the notion that if it seems dangerous, accidents happen, and proposed that if it seems dangerous, accidents dont happen. It pointed out that vehicle, road, and driver all combine in safe and efficient vehicle operation; and that as the level of improvement dropped, the drivers ability became more and more important. It described the concept of positive guidance and proposed that, at least for low-volume rural roads, consistency in design be redefined to include both geometry and positive guidance. Given measures of the relative costs and potential for accident reduction of geometry and guidance, choices could be made rationally.A.2 译文低流量农村公路的统一设计由Clarkson奥格尔斯比，H. M. ASCE(公路司)摘要：美国的200万英里的低流量的农村公路与高流量的道路不同，应采用不同的设计。它们的交通量很低，平均约110辆/日，或车辆在三分钟内通过一个高峰路段。与此相反，是一辆车每四秒的通行能力。对于大多数建于20世纪20年代和30年代的 道路几何参数都没有改变。今天，道路的改善，应根据经济的、安全的一致设计，但因为需求巨大所以资金短缺。现今高流量的道路设计经验要求路面每个功都能满足现代车辆规定的设计速度。这种做法不适合小流量的情况下，如果有可能，司机会超过任何经济实惠的设计速度。他们必须在放缓速度的情况下保证。因此需要一个统一的方法来设计，实现小流量的道路便宜、安全改进。它涉及到整合的几何设计和正面引导的方法。积极引导使用车道，交通标志和其他设备和策略，以调动司机的感官，使他们明智的驾驶。选择成本较低的几何线性与主动诱导技术将产生更安全更便宜的道路。简介美国约有约3,200,000英里(5,100,000公里)农村公路。据粗略估计约2,000,000(3,000,000公里)属于低流量，这通常包括那些每日平均双向交通量小于400辆/日的道路。这些道路大部分交通量是相当低的。有人估计平均在110辆/日，或20辆/小时。这意味着在高峰时段，车辆没三分钟通过一英里。与此相反，一个重要的两车道公路的通行能力，可能是1800辆/小时，车速可达到每英里4秒或低交通量道路的90倍。提供给高流量道路的钱是低流量道路的10倍。因此，建设新的、升级或维护量低的农村道路的战略比更高容量的道路更困难，如果用于这些目的钱是非常有限，就必须用在刀刃上。鉴于低流量道路问题的独特性，它似乎是适当的检查，并有可能重新定义何谓“在设计上的统一”。本文试图通过探讨以下内容，因为它适用于他们的任务：1、当地农村公路的发展和现状。2、 现今低交通量道路的“统一”几何标准。3、低交通量农村公路设计标准的影响因素。4、结论。当地农村公路的发展和现状本文的目的，农村地方道路是那些连通当地土地的。这些包括农场，牧场，休闲，森林或者其他。该定义不包括那些靠近郊区的道路。在过去的50年里相对较少的里程已被添加到小流量交通体系建设。他们的目的是“农民有路可行”。这些往往是狭窄的道路和路域的特点。在中西部和西部道路的宽度在第一个平方英里，是66英尺(20米)。这个宽度是给沿边缘相邻的部分土地使用权。在东部各州，许多路的宽度是窄的，通常33英尺(10米)或以下。在丘陵或多山的乡村，曲折的路线限制了道路宽度。如今，这些往往把速度限制在30英里/小时(48公里/小时)或更少。在这些早期的几年，交通工具主要是马车。在20世纪30年代，当这些土地的通路被修通时，无论车辆还是路面都不允许快速行驶，所以要求的速度很低。因为这些原因，设计速度的概念是不存在的。今天，汽车的性能与以前有很大的不同，车的尺寸和重量显着增加。此外，可能这种低交通量的农村公路在地球表面的三分之二已经铺好，用表面处理或其他方法使表面平整、无波纹或灰尘。目前，司机需要以较高速度行驶时受到交叉口或平面交叉的限制，被迫只能减缓。在更高交通量道路，其中许多已先后提高提速，很少需要这种限速措施，而当它是提醒司机精心采取措施。但因为缺钱，这种改进速度已经远远落后的低流量的乡村道路的发展。在这种情况下超过三分之二(1978年)已经维修的用作其他用途，新建或改善的机会甚微。什么都不做是解决不了低交通量道路与行驶速度之间的冲突的。政府正在通过筹集资金来达到改善或重建道路的预算通，尽管他们已经做了很多。但是差距仍然很大。这一点当然不仅适用于道路几何形状，面层和桥梁面临同样的问题。如何统一低交通量公路建设和改造的新标准如前所述，大部分需要改变几何线性的低交通量公路是在特定情况下建于50前。除了维修，改善，重建，他们几乎没有变化。当时主要的农村公路在相同的条件下建设，其几何线性不在考虑范围内。例如，致力于在1940年年底，一本由T.R. AGG编著的公路工程教科书，只有22页的整体几何线性设计。AGG说：“只要设计的