附录A 外文翻译原文 Road DesignHistory of Road DesignFirstly let me apologise for this page. It is largely text based due to the nature of it and if reading is difficult then I am sorry. This is due solely to the material covered and is the only page in the series. This is not typical as the rest have graphics or images to keep you amused. Secondly this page is very much a history of road building in the United KingdomThe first road builders of any significance in Western Europe were the Romans, who saw the ability to move quickly as essential for both military and civil reasons. It is from the Romans that the term highway comes as all their roads were elevated 1m above the local level of the land. This was to minimise the risk of an ambush, as was the best known characteristic of the roads, their lack of corners. The standards set by the Romans in terms of durability far exceeded anything achieved after the fall of the empire.The Roman approach to road design is essentially the same as that in current use. The roads were constructed of several different layers, increasing in strength from the bottom. The lowest layer was normally a rubble, intermediate layers were made of lime bound concrete and the upper layer was a flag or lime grouted stone slabs. The thickness of the layers was varied according to the local ground conditions.After the fall of the Roman Empire the road system fell into a state of disrepair and by the end of the middle ages, there was in effect no road system in the country. The only routes available were unpaved tracks, muddy and impassable in winter and dusty and impassable in summer. Diversions around particularly poor stretches resulted in sinuous alignments. The state of the roads combined with the general lawlessness at the time meant only the determined or insane traveled. The first change in this attitude came in 1555 when an Act of Parliament was passed imposing a duty on all parishes to maintain its roads. Also included in the Act was the creation of the position of a Surveyor of Highways. This was unpaid and under resourced though and when combined with the lack of technical skills it is no surprise that the post became distinctly unpopular and ineffective. This lack of resources meant that the first major road was not established until the latter part of the seventeenth century. These roads were known as turnpike roads where the road user paid a toll. The first sections were known as the Great North Road and has since become the A1 trunk road. In the following century Turnpike Trusts were established to provide turnpike roads along major routes in the United kingdom. In this improved financial climate roadbuilding techniques evolved thanks to the work of pioneers such as Telford and Macadam. By about 1830 a system of well paved built roads existed such that the only constraints on road traffic and travel times were imposed by the nature of road vehicles. The next improvement came about with the advent of the railways. With rapid transport between towns now possible, the turnpikes became uneconomical and whilst roadbuilding in towns continued apace the turnpike trusts collapsed. Legislation in the late 19th century set the scene for the current administrative arrangements for highway construction and maintenance but the technology remained primitive and empirical. Only in recent years has that situation improved to any extent and even now most road design is based on empirical relationships and experimental work.The present situation is almost a complete reversal, with funding for new roads coming from the private sector. In exchange for building and maintaining the road the owners are paid a toll by the government for each vehicle using the road, a sort of modern turnpike system.Traffic Analysis Road loading takes many different forms, from a bicycle to multi-axled truck and trailer combinations. Traffic Analysis can be split into two well defined areas: Traffic Volume - This is the role of the Traffic Engineer and does not normally concern the Civil Engineer. This is not relevant to determining the load on the road, only the size and layout. Traffic Loading - This is the role of the Pavement Engineer and involves determining the loading on the road to be carried forward to the Pavement Design. Traffic VolumeThe role of the traffic engineer is to enable all traffic to travel on the road at a reasonable speed and with an appropriate degree of safety. This is not the loading that is used in the Pavement Design. These values are used to determine the road width only. With relation to the volume of traffic using the road, the passenger car is adopted as the standard unit and other vehicles are assessed in terms of passenger car units (pcu).Differences in the urban and rural situations arise due to the variation of speeds in the two areas. Decisions on road width are not normally made on total traffic flow per day as this is misleading but r