public way, usually maintained by governmental authority, for the passage of vehicles, people, or animals. Roads in cities or towns are also called streets, lanes, avenues, or boulevards. Roads that connect populated areas to one another are often called motorways or highways.


Road building, from very ancient times, has been one of the first signs of an advancing civilization. As the cities of early civilizations increased in size and density of population, communication with other regions became necessary as a means of bringing in food supplies and carrying on other commerce. Early road builders included the Mesopotamians, as far back as 3500 BC; the Chinese, who had built the Silk Road, the world's longest road for some 2,000 years and had developed a road system by the 11th century BC; and the Incas of South America, who built an advanced network of roads through the Andes, including galleries cut through solid rock. The writings of the 1st-century Greek geographer Strabo record a system of roads radiating from ancient Babylon; the writings of Herodotus, a Greek historian of the 5th century BC, mention the highways built in Egypt for the transport of materials used in building the pyramids and other monumental structures constructed under the pharaohs.
The earliest of the ancient road builders whose work still survives were the Romans. The Appian Way was begun about 312 BC, and the Flaminian Way, about 220 BC. At the height of its power, the Roman Empire had a road system of about 80,000 km (50,000 mi), consisting of 29 highways radiating from the city of Rome, and a network of roads covering every important conquered province, including Britain. The Roman roads were 90 to 120 cm (3 to 4 ft) thick, and consisted of three layers of successively finer stones set in mortar, with a layer of fitted stone blocks on top. By Roman law, the right of use of the roads belonged to all of the public, but the maintenance of the roadway was the responsibility of the inhabitants of the district through which the road ran. This system was effective in maintaining good roads so long as a strong central authority existed to enforce it; during the Middle Ages (from about the 5th century to the 15th century), with the absence of the central authority of the Roman Empire, national road systems largely disappeared.
In the middle of the 17th century the French government instituted a system of enforced local labour on the roads, and built about 24,000 km (15,000 mi) of main roads by this method. Around the same time Parliament instituted a system of granting franchises to private companies for the maintenance of public roads, allowing the companies to charge tolls for the use of the roads. More than 1,000 turnpike companies, maintaining 32,000 km (20,000 mi) of roads, were in operation in Britain in the 1830s, when the competition from railways began to make the turnpike system less profitable for the operators.
During the first three decades of the 19th century, methods of highway construction were pioneered by the work of two British engineers, Thomas Telford and John Loudon McAdam, and by the French road engineer Pierre-Marie-Jérôme Trésaguet. Telford's system of road building involved digging a trench and installing a foundation of heavy rock. The foundation was raised in the centre so that the finished road was sloped away from the centre, allowing drainage to take place. The topmost layer of the road consisted of a 15-cm (6-in) layer of compacted broken stone.
McAdam held that well-drained earth would support any load. In McAdam's method of road construction, the finishing layer of broken stone was placed directly on a foundation of earth that was raised above the surrounding ground to ensure the foundation drained properly. McAdam's system, called macadamization, was generally adopted at the time, especially in Europe. When heavy trucks were used in World War I, however, the earth foundations of macadamized roads could not bear the heavy road load. As a result, Telford's system was adopted for the construction of heavy-duty roads, because it furnished a better distribution of road load over the underlying subsoil. Another road pioneer, John Metcalf, built more than 290 km (180 mi) of roads in Britain.
Early American roads were built by a breaking and blazing of trails through difficult terrain; in open country, the continued use of a track usually wore into a well-marked route. Some examples of these types of roads were the great trails of the West: the Oregon, the Santa Fe, and the Overland trails.
In the eastern states, the first extensive movement for the improvement of roads began immediately after the American war of Independence, with the establishment of turnpikes, or toll roads, to finance the heavy repairs.
During the period of railway expansion in the latter half of the 19th century, the development of highways suffered a corresponding decline. During this period, too, brick and sheet asphalt were introduced as pavement for city streets.

Road-Building Programmes in the 20th Century

The popularity of the bicycle, which began in the 1880s, and the introduction in the United States of the motor car in the 1890s led to a need for more and better highways. By 1917 all American states had adopted programmes for controlling local road construction. In 1904 almost 3.2 million km (2 million mi) of unpaved roads and about 248,000 km (154,000 mi) of pavement were in use in the United States. In the same year a great increase in motor vehicle traffic began, which, over the next decade, revealed the inadequacy of older methods of paving. As a corrective, coal tars, tars, and oils were used, first as surface binders and dust layers, then as penetration binders, for macadam pavements. Bituminous pavement was used largely in the cities; this type of paving material consisted of graded sizes of broken stone that was coated with a bituminous material, such as asphalt or tar, before laying, and was compacted with a heavy roller afterwards. Bituminous pavement is more durable than macadam pavements penetrated with a binder. Rural highways made of macadam pavements penetrated with a bituminous binder could not hold up under the sudden increase of heavy goods traffic during World War I. This heavy traffic forced the adoption of highway construction that included subsoil drainage, an adequate foundation, a concrete base, and an additional surface layer of concrete or bituminous pavement.
The first motorway network was the Italian autostrada system, built as undivided three-lane roadways during the 1920s. The truly modern highway system was the German autobahn, which was constructed in the 1930s. Consisting of three north-south routes, three east-west routes, and dual-lane roadways, the autobahn network was designed for large (mainly military) traffic volumes and speeds in excess of 165 km/hr (100 mph).
In Britain road building and maintenance had been organized locally, which was inadequate for modern requirements. By 1919 the roadway network was divided into two classes of road, with building expenditure to be borne by national government. Legislation in 1949 authorized new or existing roads as motorways. By the 1950s most European countries had a system of main highways, with Germany's remaining the most advanced.

Modern Roads

The important variables taken into consideration in modern road engineering are the slope of the land upon which the road is to be built, the ability of the pavement to support the load it is expected to carry, the predicted intensity of road use, the nature of the underlying soil, and the composition and thickness of the paving structure. The pavement itself can either be rigid, allowing little latitude for bending, or flexible. Flexible paving uses a mixture of coarse or fine aggregate (crushed stone, gravel, and sand) with bituminous material obtained from asphalt or petroleum, and tar products. This mixture is compact and yet plastic enough to absorb enormous shocks and support a heavy volume of traffic. Rigid pavements are constructed with a mixture of portland cement and coarse and fine aggregate. The thickness of the paving can vary from 15 to 45 cm (6 to 18 in), depending on the volume of traffic to be carried, and steel reinforcement is often used to prevent cracking. Sand or fine gravel is used as a base under the paving for increased support.
Modern highways are constructed in almost straight lines across open country, rather than following old or established routes. Congested areas are avoided or passed through on express parkways, elevated highways, or tunnels. Safety is increased by separating traffic, and by controlling access. Vehicles travelling in opposite directions are separated by a median. Modern highways are designed so that motorists can enter or leave a highway only at interchanges where the highway and another major road intersect. One of the roads crosses over the other on a bridge, and ramps connect the two roads so motorists can have access to the connecting road without disturbing the flow of traffic. Other characteristics of a modern highway include adequate lighting for night driving, wide shoulders for parking out of traffic, speed-change lanes, climbing lanes, reversible lanes, bus lanes, reflective signs and pavement markings, and traffic-control signals.
Today, motorways in Britain carry around 15 per cent of all traffic, and trunk roads about 17 per cent. In 1994 55 motorway and trunk roads were under construction. These include the second crossing over the River Severn and a second road bridge across the Firth of Forth, which is likely to be privately funded.
The American Interstate Highway System is a 68,400-km (42,500-mi) network of limited-access highways. This carefully designed system enables motorists to drive from coast to coast and border to border without an intersection or traffic signal. It carries about 20 per cent of the country's motor-vehicle traffic, although it makes up only 1 per cent of its roads and streets. The system is designed for safe, efficient driving, with gentle curves, easy grades and long sight distances. Entering and leaving the highway system is permitted only at planned interchanges, and median areas between roadways are generally at least 11 m (36 ft) wide, except in mountainous and urban locations. By the early 1990s, nearly the entire Interstate Highway System had been completed and opened to traffic.

Contributed by: Federal Highway Administration; International Road Federation "Road," Microsoft(R) Encarta(R) 96 Encyclopedia. (c) 1993-1995 Microsoft Corporation. All rights reserved. (c) Funk & Wagnalls Corporation. All rights reserved.
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