ROADS AND HIGHWAYS

traveled way on which people, animals, or wheeled vehicles move. In modern usage the term road describes a rural, lesser traveled way, while the word street denotes an urban roadway. Highway refers to a major rural traveled way; more recently it has been used for a road, in either a rural or urban area, where points of entrance and exit for traffic are limited and controlled. The most ancient name for these arteries of travel seems to be the antecedent of the modern way. Way stems from the Middle English wey, which in turn branches from the Latin veho (I carry), derived from the Sanskrit vah (carry, go, or move). The word highway goes back to the elevated Roman roads that had a mound or hill formed by earth from the side ditches thrown toward the centre, thus high way. The word street originates with the Latin strata (initially, paved) and later strata via (a way paved with stones). Street was used by the Anglo-Saxons for all the roads that they inherited from the Romans. By the Middle Ages, constructed roads were to be found only in the towns, and so street took on its modern limited application to town roads. The more recent word road, derived from the Old English word rd (to ride) and the Middle English rode or rade (a mounted journey), is now used to indicate all vehicular ways. Modern roads can be classified by type or function. The basic type is the conventional undivided two-way road. Beyond this are divided roads, expressways (divided roads with most side access controlled and some minor at-grade intersections), and freeways (expressways with side access fully controlled and no at-grade intersections). An access-controlled road with direct user charges is known as a tollway. In the United Kingdom freeways and expressways are referred to as motorways. Functional road types are local streets, which serve only adjacent properties and do not carry through traffic; collector, distributor, and feeder roads, which carry only through traffic from their own area; arterial roads, which carry through traffic from adjacent areas and are the major roads within a region or population centre; and highways, which are the major roads between regions or population centres. The first half of this article traces the history of roads from earliest times to the present, exploring the factors that have influenced their development and suggesting that in many ways roads have directly reflected the conditions and attitudes of their times. The road is thus one of the oldest continuous and traceable metaphors for civilization and society. The second half of the article explains the factors behind the design, construction, and operation of a modern road. It is shown that a road must interact closely and carefully with the terrain and community through which it passes, with changing vehicle technology, with information technologies, and with the various abilities, deficiencies, and frailties of the individual driver. Additional reading M.G. Lay, Ways of the World: A History of the World's Roads and of the Vehicles That Used Them (1992), provides an overview, while his Handbook of Road Technology, 2nd ed., 2 vol. (1990), includes technical information on planning, pavements, traffic, and transport. Additional historical works are Hermann Schreiber, The History of Roads: From Amber Route to Motorway (1961; originally published in German, 1959), on the ancient roads of Asia, Europe, and Egypt and the Incan roads in South America; R.J. Forbes, Roads to c. 1900, in Charles Singer et al. (eds.), A History of Technology, vol. 4 (1958), pp. 520547; W.J. Reader, Macadam: The McAdam Family and the Turnpike Roads, 17981861 (1980), treating the roads in 19th-century Great Britain; and United States, Federal Highway Administration, America's Highways, 17761976 (1977), chronicling federal aid to transportation in the United States.Aspects of road engineering and operation are detailed in Highway Capacity Manual, 2nd ed., rev. (1993), published by the Transportation Research Board (United States); American Association of State Highway and Transportation Officials, AASHTO Guide for Design of Pavement Structures, vol. 1, new ed. (1993) and vol. 2 (1986); and several publications of the Organisation for Economic Cooperation and Development, Road Research Programme: Proceedings of the International Symposium on the Effects of Speed Limits on Traffic Accidents and Fuel Consumption (1982), Traffic Capacity of Major Routes (1983), Impacts of Heavy Freight Vehicles (1983), and Road Surface Characteristics: Their Interaction and Their Optimisation (1984). International traffic regulations are presented in Peter Kincaid, The Rule of the Road (1986). Maxwell Gordon Lay The modern road Road engineering Since the beginning of the 20th century, as the automobile and truck have offered ever higher levels of mobility, vehicle ownership per head of population has increased. Road needs have been strongly influenced by this popularity and also by the mass movement of people to cities and thence to suburban fringesa trend that has led to increasing travel needs and road congestion and to low-density cities, which are difficult to service by public transport. Often the building of new roads to alleviate such problems has encouraged further urban sprawl and yet more road travel. Long-term solutions require the provision of alternatives to car and truck transport, controls over land use, and the proper pricing of road travel. To this end, road managers must be concerned not merely with lines on maps but also with the number, type, speed, and loading of individual vehicles, the safety, comfort, and convenience of the traveling public, and the health and welfare of bystanders and adjoining property owners. Ideally, the development of a major road system is an orderly, continuous process. The process follows several steps: assessing road needs and transport options; planning a system to meet those needs; designing an economically, socially, and environmentally acceptable set of roads; obtaining the required approval and financing; building, operating, and maintaining the system; and providing for future extensions and reconstruction. Planning Road needs are closely associated with the relative location of centres of population, commerce, industry, and transportation. Traffic between two centres is approximately proportional to their populations and inversely proportional to the distance between them. Estimating traffic on a route thus requires a prediction of future population growth and economic activity, an estimation of their effects on land use and travel needs, and a knowledge of any potential transport alternatives. The key variables defining road needs are the traffic volumes, tonnages, and speeds to be expected throughout the road's life. Once the traffic demand has been estimated, it is necessary to predict the extent of the road works needed to handle that traffic. A starting point in these calculations is offered by surveys of the origins, destinations, and route choices of present traffic; computer models are then used to estimate future traffic volumes on each proposed route. Estimates of route choice are based on the understanding that most drivers select their estimate of the quickest, shortest, or cheapest route. Consideration in planning is also given to the effect of new traffic on existing streets, roads, and parking provisions. Where feasible, the next step in planning a road system is to refine the selected route to a narrow corridor. The various alignment options are drawn, considering the local terrain and conditions. The economic, social, and environmental benefits and costs of these options are discussed with relevant official and community groups until an acceptable specific route is determined.