History of roads and highways. Part II

Inca roads of South America. Across the Atlantic, the period witnessed the rise of another notable road-building empire, that of the Incas. The Inca road system extended from Quito, Ecuador, through Cuzco, Peru, and as far south as Santiago, Chile. It included two parallel roadways, one along the coast about 2,250 miles in length, the other following the Andes about 3,400 miles in length with a number of cross connections. At its zenith, when the Spaniards arrived early in the 16th century, a network of some 14,000 miles of road served an area of about 750,000 square miles (1,940,000 square kilometres) in which lived nearly 10 million people. The network was praised by 16th-century explorers as superior to that in contemporary Europe.

The Andes route was remarkable. The roadway was 25 feet wide and traversed the loftiest ranges. It included galleries cut into solid rock and retaining walls built up for hundreds of feet to support the roadway. Ravines and chasms were filled with solid masonry, suspension bridges with wool or fibre cables crossed the wider mountain streams, and stone surfacing was used in difficult areas. The steeper gradients were surmounted by steps cut m the rocks Traffic consisted entirely of pack animals (llamas) and people on foot; the Inca lacked the wheel. Yet they operated a swift foot courier system and a visual signaling system along the roadway from watchtower to watchtower.

Early American roads. The first settlers in North America found a wilderness. They located their homes along the rivers and bays and used the water for transportation. As new settlers went inland, they usually built crude roads to the nearest wharf. Until after the War of 1812, people traveled mainly on foot or on horseback.

The first extensive hard-surfaced road was completed in 1794. This road was called the Lancaster (Pa.) Turnpike. It was 62 miles (100 kilometers) long and was surfaced with hand-broken stone and gravel. In the next 40 years, many turnpikes were built. Most surfaces were of earth, gravel, or broken stone. Some roads were covered with logs or planks, laid crosswise. Where logs were used, the roads were called corduroy roads. Both corduroy roads and plank roads were very bumpy.

In 1830, it looked as though a great period of road-building was about to begin. But in that year, the steam locomotive was successfully operated and rapid development of railroads began. Many people became convinced that the railroad was the best means for travel over long distances. From 1830 to 1900, there was little change in the surfacing materials for roads and highways. Even in cities, only wood blocks, brick, and cobblestones were used for surfacing roads.

Modern roads. By 1900, there was a growing demand for good roads. Roads that extended a short distance were built in the United States to give farmers access to the railroads, which hauled farm products. The first freeway was completed in 1921 in the Grunewald, a forest area in Berlin, Germany. This road, which was 6 miles (10 kilometers) long, served as a route for suburban commuters and as a race track. In 1925, the United States adopted its system of numbering highways, which was suggested by Wisconsin highway engineer A. R. Hirst in 1917. Few U.S. highways were built from the Great Depression of the 1930'з until the end of World War II in 1945.

In 1934, Germany began building its Autobahn (expressway) system. This extensive system featured divided highways, grade-separated interchanges, and well-designed service areas. A section of the Pennsylvania Turnpike, the first U.S. freeway, opened in 1940. This section ran from Middlesex (near Carlisle) to Irwin. In California, the Arroyo Seco Parkway opened in 1940 between Pasadena and Los Angeles. The Pennsylvania Turnpike and the Arroyo Seco Parkway soon demonstrated that the population quickly grew in areas where freeways were built.

In the 1950's, many United States industry and civic groups joined in supporting highway improvement programs. The federal interstate highway system, which was begun in 1956, was nearly complete by the early 1990's. Engineers today continue to seek ways of improving highway safety through better construction and improving traffic flow through the use of computers.

Text D.

The Master Road Builders.

Gradual technological improvements in the 17-th and 18-th centuries increased commercial travel, improved vehicles and the breeding of better horses. Rural roads became impassable in wet weather. These factors created an increasing demand for better roads.

Up to this time roads similar to the Roman roads were built. However, owing to a scarcity of a suitable material and the high cost of labour, the amount of stone material used was progressively reduced and the work was carried out less thoroughly. Research was carried out to find out more rational methods of using stone for pavement construction which would reduce both the amount of labour and the cost. And in the last half of the 18-th century the fathers of modern road building and road maintenance appeared in France and Britain.

Tresaquet.In France in 1764, Pierre Tresaquet, became an engineer of bridges and roads in Limoges. He developed an entirely new type of relatively light road surface, based on theory that the underlying natural formation should support the load.

His standard cross section, 18 feet wide, consisted of an eight-inch-thick course of uniform stones laid edgewise on the natural formation and covered by a two-inch layer of broken stone. The second layer was topped with one-inch layer of smaller broken stone. In order to maintain surface level Tresaquest's pavement was placed in an excavated trench— a technique that made drainage a difficult problem.

McAdam.The greatest advance came from John McAdam, born in 1756 in Scotland. He reached major heights in his road-building career after 1804 when he was appointed general surveyor for Bristol, then the most important port city in London. The roads leading to Bristol were in poor condition. There he showed that traffic could be supported by a relatively thin layer of small, single-sized pieces of broken stone placed and compacted on a well-drained natural formation and covered by an impermeable surface of smaller stones.

Mc Adam is famous for the surface he developed for roads. This kind of surface, called macadam, is still used today. Mc Adam also stressed the importance of proper drainage to keep roads on a solid foundation. Drainage was essential to the success of Mc Adam’s method and he required the pavement to be elevated above the surrounding surface. The structural layer of broken stone was eight inches thick and used stone of two or three inches maximum size laid in layers and compacted by traffic. The top layer was 2 inches thick, using three-quarter-inch stone to fill surface voids between the large stones. Continuous maintenance was essential.

Russian engineers were the first ones to construct granular surfacing laid on sand base which are now widely used in other countries. The use of a sand base permitted the cost of construction to be reduced and the removal of water from the subgrade to be facilitated. It helped to increase subgrade stability.

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