外文翻譯---低流量農(nóng)村公路的統(tǒng)一設(shè)計

1、附錄 A 外文翻譯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 diffe

2、rent 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 p

3、eak 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 des

4、igns 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

5、 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 cons

6、istent 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, signi

7、ng, 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.IN

8、TRODUCTIONThere 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

9、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. Th

10、is 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 mil

11、e 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 constr

12、uction, upgrading, or maintenance of low-volume rural roads will be entirely different than for higher-volume roads, if the very limited money available How CONSISTENCY IN PRESENT-DAY GEOMETRIC STANDARDS FOR NEW CONSTRU

13、CTION 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 maintenanc

14、e, 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

15、 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

16、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 judgment—that does

17、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 fea

18、tures 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 19

19、50 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 publ

20、ished 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 aspe

21、cts 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

22、 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 STANDARD

23、SFOR 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

24、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 Admini

25、stration. 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

26、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 “