外文翻譯---低流量農(nóng)村公路的統(tǒng)一設(shè)計-文庫吧資料
2025-01-24 14:37本頁面
【正文】 ne 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 presentday geometric standards for new construction or renovation of lowvolume roads has developed.3. Factors that have impinged on design standards for lowvolume 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 lowvolume 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 rightsofway. In the middle west and west, where much of the land had been laid out in sections one mile square, rightsofway were 66 ft (20 m). This width was dedicated to land access along the edges of adjacent sections. In the eastern states, many rightsofway 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 horsedrawn vehicle. Even in the 1930s, when the last of these landaccess 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 twothirds of this lowvolume 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 lowvolume rural roads because money has been scarce. Of that available, more than twothirds (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 lowvolume rural roads have done nothing to overe 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.Ho
環(huán)評公示相關(guān)推薦
鄂ICP備17016276號-1