road, strip of land used for transportation. The history of roads has been related to the centralizing of populations in powerful cities, which the roads have served for military purposes and for trade, the collection of supplies, and tribute. In the Middle East, in N Mesopotamia, scientists have found evidence of a network of roads dating back to perhaps 3000 B.C. In Persia, between 500 and 400 B.C., all the provinces were connected with the capital, Susa, by roads, one of them 1,500 mi (2,400 km) long. The ancient Greeks, cherishing the independence of their city-states and opposing centralization, did relatively little road making.

The Roman roads, however, are famous. In Italy and in every region that the Romans conquered, they built roads so durable that parts of them yet remain serviceable. The Roman roads were generally straight, even over steep grades. The surface, made of large slabs of hard stone, rested on a bed of smaller stones and cement about 3 ft (91 cm) thick.

From the fall of the Roman Empire until the 19th cent., European roads generally were neglected and hard to travel. People usually walked, rode horses, or were carried in sedan chairs. Goods were transported by pack animals. In France, Louis XIV and Napoleon built good roads for military purposes. Elsewhere on the Continent roads were not much improved before the middle of the 19th cent. In Great Britain two Scottish engineers, Thomas Telford and John L. McAdam, were responsible for the development of the macadam road (see pavement). The expansion of the Industrial Revolution brought this and other road improvements to the Continent, although the emphasis was on railroad construction until after the invention of the automobile.

In the Americas the Inca empire was remarkable for its fine roads. In what is now the United States, however, the waterways were the normal mode of travel for Native Americans, and their trails, though numerous, were often simply footpaths. These were used by white settlers and were eventually widened to make wagon trails. The increasing use of stagecoaches led to some improvement, and the turnpike, or toll road, was introduced at the beginning of the 19th cent. Although the planning and building of road arteries, notably the National Road, marked the early years of the century, canals and then railroads took precedence.

The invention and mass production of the automobile made the road became paramount again. Hard-surfaced highways were stretched across the entire land in a relatively few years. The building of roads became a major branch of engineering, and even the most difficult obstacles were surmounted. Roads have helped greatly to equalize and unify large heterogeneous nations. In the United States the Interstate Highway System consists of 42,793 mi (68,869 km) of roads (all but a few miles of which are completed) connecting every major city. Other well-known road networks which serve to unify large areas include Germany's Autobahn, the Trans-Canada Highway, and the Pan-American Highway. An ambitious, 23-nation agreement to link Asia with a network of highways was signed in 2004.

Traveled way on which people, animals, or wheeled vehicles move. The earliest roads developed from paths and trails and appeared with the invention of wheeled vehicles, around 3000 BC. Road systems developed to facilitate trade in early civilizations; the first major road extended 1,775 mi (2,857 km) from the Persian Gulf to the Aegean Sea and was used circa 3500–300 BC. The Romans used roads to maintain control of their empire, with over 53,000 mi (85,000 km) of roadways extending across its lands; Roman construction techniques and design remained the most advanced until the late 1700s. In the early 19th century invention of macadam road construction provided a quick and durable method for building roads, and asphalt and concrete also began to be used. Motorized traffic in the 20th century led to the limited-access highway, the first of which was a parkway in New York City (1925). Superhighways also appeared in Italy and Germany in the 1930s. In the 1950s the U.S. interstate highway system was inaugurated to link the country's major cities.

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formerly Ledo Road

Former military highway, Asia. It was 478 mi (769 km) long and linked northeastern India with the Burma Road. In World War II, U.S. Army engineers and Chinese troops constructed it to link the railheads of Ledo, India, and Mogaung, Burma. Named for Gen. Joseph Stilwell, it crossed into Burma (Myanmar) through the difficult Pangsau Pass of the Patkai Range.

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Highway, South Asia. It runs 717 mi (1,154 km) from Lashio (in eastern Burma, now Myanmar) northeast to Kunming (in Yunnan, China). An extension runs east through China from Kunming, then north to Chongqing. Completed in 1939, it functioned as a supply route to the interior of China, carrying war goods. It was seized by the Japanese in 1942 and reopened when it was connected to the Stilwell Road from India. Its importance diminished after World War II, but it has remained a link in a 2,100-mi (3,400-km) road system from Yangôn, Myanmar, to Chongqing.

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A road is an identifiable route, way or path between two or more places. Roads are typically smoothed, paved, or otherwise prepared to allow easy travel; though they need not be, and historically many roads were simply recognizable routes without any formal construction or maintenance.

The term was also commonly used to refer to roadsteads, waterways that lent themselves to use by shipping. Notable examples being Hampton Roads, in Virginia, and Castle Roads, in Bermuda (also formerly in Virginia).

In urban areas roads may pass through a city or village and be named as streets, serving a dual function as urban space easement and route. Economics and society depend heavily on efficient roads. In the European Union (EU) 44% of all goods are moved by trucks over roads and 85% of all persons are transported by cars, buses or coaches on roads.

The United States has the largest network of roadways of any country with 6,430,366 km (2005). India has the second largest road system in the world with 3,383,344 km (2002). People's Republic of China is third with 1,870,661 km of roadway (2004). When looking only at expressways the National Trunk Highway System (NTHS) in People's Republic of China has a total length of 45,000 km at the end of 2006, second only to the United States with 90,000 km in 2005.

History

That the first pathways were the trails made by animals has not been universally accepted, arguing that animals do not follow constant paths. Others believe that some roads originated from humans following animal trails. The Icknield Way is given as an example of this type road origination, where man and animal both selected the same natural line. By about 10,000 BC, rough pathways were used by human travelers.

Historical road construction dating to 4000 BC

• Stone paved streets are found in the city of Ur in the Middle East dating back to 4000 BC
• Corduroy roads (log roads) are found dating to 4,000 BC in Glastonbury, England
• The timber trackway; Sweet Track causeway in England, is one of the oldest engineered roads discovered and the oldest timber trackway discovered in Northern Europe. Built in winter 3807 BC or spring 3806 BC, tree-ring dating (Dendrochronology) enabled very precise dating. It has been claimed to be the oldest road in the world.
• Brick paved streets were used in India as early as 3000 BC
• In 500 BC, Darius I the Great started an extensive road system for Persia (Iran), including the famous Royal Road which was one of the finest highways of its time. The road remained in use after Roman times.
• In ancient times, transport by river was far easier and faster than transport by road, especially considering the cost of road construction and the difference in carrying capacity between carts and river barges. A hybrid of road transport and ship transport beginning in about 1740 is the horse-drawn boat in which the horse follows a cleared path along the river bank.
• From about 312 BC, the Roman Empire built straight strong stone Roman roads throughout Europe and North Africa, in support of its military campaigns. At its peak the Roman Empire was connected by 29 major roads moving out from Rome and covering 78,000 kilometers or 52,964 Roman miles of paved roads.
• In the 700s AD, many roads were built throughout the Arab Empire. The most sophisticated roads were those of the Baghdad, Iraq, which were paved with tar in the 8th century. Tar was derived from petroleum, accessed from oil fields in the region, through the chemical process of destructive distillation.
• In the 1600s road construction and maintenance in Britain was traditionally done on a local parish basis. This resulted in a poor and variable state of roads. To remedy this, the first of the "Turnpike Trusts" was established around 1706, to build good roads and collect tolls from passing vehicles. Eventually there were approximately 1,100 Trusts in Britain and some 36,800 km of engineered roads. The Rebecca Riots in Carmarthenshire and Rhayader from 1839 to 1844 contributed to a Royal Commission leading to the demise of the system in 1844.

Road transport economics

Transport economics is a branch of economics that deals with the allocation of resources within the transport sector and has strong linkages with civil engineering. Transport economics differs from some other branches of economics in that the assumption of a spaceless, instantaneous economy does not hold. People and goods flow over networks at certain speeds. Demands peak. Advanced ticket purchase is often induced by lower fares. The networks themselves may or may not be competitive. A single trip (the final good from the point-of-view of the consumer) may require bundling the services provided by several firms, agencies and modes.

Although transport systems follow the same supply and demand theory as other industries, the complications of network effects and choices between non-similar goods (e.g. car and bus travel) make estimating the demand for transportation facilities difficult. The development of models to estimate the likely choices between the non-similar goods involved in transport decisions "discrete choice" models led to the development of the important branch of econometrics, and a Nobel Prize for Daniel McFadden.

In transport, demand can be measured in numbers of journeys made or in total distance traveled across all journeys (e.g. passenger-kilometres for public transport or vehicle-kilometres of travel (VKT) for private transport). Supply is considered to be a measure of capacity. The price of the good (travel) is measured using the generalised cost of travel, which includes both money and time expenditure. The effect of increases in supply (capacity) are of particular interest in transport economics (see induced demand), as the potential environmental consequences are significant.

Road building and maintenance is an area of economic activity that remains dominated by the public sector (though often through private contractors). Roads (except those on private property that are not accessible to the general public) are typically paid for by taxes (often raised through levies on fuel), though some public roads, especially highways are funded by tolls.

Environmental aspects

Motor vehicle traffic on roads generate noise pollution especially at higher operating speeds. Therefore, considerable noise health effects are expected from road systems used by large numbers of motor vehicles. Noise mitigation strategies exist to reduce sound levels at nearby sensitive receptors. The idea that road design could be influenced by acoustical engineering considerations first arose about 1973.

Motor vehicles operating on roads contribute emissions, particularly for congested city street conditions and other low speed circumstances. Concentrations of air pollutants and adverse respiratory health effects are greater near the road than at some distance away from the road. Road dust dust kicked up by vehicles may cause allergies.

Driving on the right or the left

Traffic flows on the right or on the left side of the road depending on the country. In countries where traffic flows on the right, traffic signs are mostly on the right side of the road, roundabouts and traffic circles go counter-clockwise, and pedestrians crossing a two-way road should watch out for traffic from the left first. In countries where traffic flows on the left, the reverse is true.

About 34% of the world by population drive on the left, and 66% keep right. By roadway distances, about 28% drive on the left, and 72% on the right, even though originally most traffic drove on the left worldwide.

Construction

Road construction requires the creation of a continuous right-of-way, overcoming geographic obstacles and having grades low enough to permit vehicle or foot travel. ^(pg15) and may be required to meet standards set by law or official guidelines. The process is often begun with the removal of earth and rock by digging or blasting, construction of embankments, bridges and tunnels, and removal of vegetation (this may involve deforestation) and followed by the laying of pavement material. A variety of road building equipment is employed in road building.

After design, approval, planning, legal and environmental considerations have been addressed alignment of the road is set out by a surveyor. The Radii and gradient are designed and staked out to best suit the natural ground levels and minimize the amount of cut and fill. ^(page34) Great care is taken to preserve reference Benchmarks ^(page59)

Roadways are designed and built for primary use by vehicular and pedestrian traffic. Storm drainage and environmental considerations are a major concern. Erosion and sediment controls are constructed to prevent detrimental effects. Drainage lines are laid with sealed joints in the road easement with runoff coefficients and characteristics adequate for the land zoning and storm water system. Drainage systems must be capable of carrying the ultimate design flow from the upstream catchment with approval for the outfall from the appropriate authority to a watercourse, creek, river or the sea for drainage discharge. ^{(page38 to 40)}

A Borrow pit (source for obtaining fill, gravel, and rock) and a water source should be located near or in reasonable distance to the road construction site. Approval from local authorities may be required to draw water or for working (crushing and screening) of materials for construction needs. The top soil and vegetation is removed from the borrow pit and stockpiled for subsequent rehabilitation of the extraction area. Side slopes in the excavation area not steeper than one vertical to two horizontal for safety reasons. ^{(page 53 to 56 )}

Old road surfaces, fences, and buildings may need to be removed before construction can begin. Trees in the road construction area may be marked for retention. These protected trees should not have the topsoil within the area of the tree's drip line removed and the area should be kept clear of construction material and equipment. Compensation or replacement may be required if a protected tree is damaged. Much of the vegetation may be mulched and put aside for use during reinstatement. The topsoil is usually stripped and stockpiled nearby for rehabilitation of newly constructed embankments along the road. Stumps and roots are removed and holes filled as required before the earthwork begins. Final rehabilitation after road construction is completed will include seeding, planting, watering and other activities to reinstate the area to be consistent with the untouched surrounding areas. ^{(page 66 to 67 )}

Processes during earthwork include excavation, removal of material to spoil, filling, compacting, construction and trimming. If rock or other unsuitable material is discovered it is removed, moisture content is managed and replaced with standard fill compacted to 90% relative compaction. Generally blasting of rock is discouraged in the road bed. When a depression must be filled to come up to the road grade the native bed is compacted after the topsoil has been removed. The fill is made by the "compacted layer method" where a layer of fill is spread then compacted to specifications, the process is repeated until the desired grade is reached. ^{(page 68 to 69 )}

General fill material should be free of organics, meet minimum California bearing ratio (CBR) results and have a low plasticity index. Select fill (sieved) should be composed of gravel, decomposed rock or broken rock below a specified Particle size and be free of large lumps of clay. Sand clay fill may also be used. The road bed must be "proof rolled" after each layer of fill is compacted. If a roller passes over an area without creating visible deformation or spring the section is deemed to comply. ^{(page 70 to 72 )}

The completed road way is finished by paving or left with a gravel or other natural surface. The type of road surface is dependent on economic factors and expected usage. Safety improvements like Traffic signs, Crash barriers, Raised pavement markers, and other forms of Road surface marking are installed.

Duplication

When a single carriageway road is converted into dual carriageway by building a second separate carriageway alongside the first, it is usually referred to as duplication or twinning. The original carriageway is changed from two-way to become one-way, while the new carriageway is one-way in the opposite direction. In the same way as converting railway lines from single track to double track, the new carriageway is not always constructed directly alongside the existing carriageway.

Maintenance

Like all structures, roads deteriorate over time. Deterioration is primarily due to accumulated damage from vehicles, however environmental effects such as frost heaves, thermal cracking and oxidation often contribute. According to a series of experiments carried out in the late 1950s, called the AASHO Road Test, it was empirically determined that the effective damage done to the road is roughly proportional to the 4th power of axle weight . A typical tractor-trailer weighing 80,000 pounds (36.287 t) with 8,000 pounds (3.6287 t) on the steer axle and 36,000 pounds (16.329 t) on both of the tandem axle groups is expected to do 7,800 times more damage than a passenger vehicle with 2,000 pounds (0.907 t) on each axle. Potholes on roads are caused by rain damage and vehicle braking or related construction works.

Pavements are designed for an expected service life or design life. In some UK countries the standard design life is 40 years for new bitumen and concrete pavement. Maintenance is considered in the whole life cost of the road with service at 10, 20 and 30 year milestones. Roads can be and are designed for a variety of lives (8-, 15-, 30-, and 60-year designs). When pavement lasts longer then its intended life, it may have been overbuilt, and the original costs may have been too high. When a pavement fails before its intended design life, the owner may have excessive repair and rehabilitation costs. Many concrete pavements built since the 1950s have significantly outlived their intended design lives. Some roads like Chicago, Illinois's "Wacker Drive", a major two-level viaduct in downtown area are being rebuilt with a designed service life of 100 years.

Virtually all roads require some form of maintenance before they come to the end of their service life. Pro-active agencies continually monitor road conditions and apply preventive maintenance treatments as needed to prolong the lifespan of their roads. Technically advanced agencies monitior the road network surface condition with sophisticated equipment such as laser/inertial Profilometers. These measurements include road curvature, cross slope, unevenness, roughness, rutting and texture (roads). This data is fed into a pavement management system, which recommends the best maintenance or construction treatment to correct the damage that has occurred.

Maintenance treatments for asphalt concrete generally include crack sealing, surface rejuvenating, fog sealing, micro-milling and surface treatments. Thin surfacing preserves, protects and improves the functional condition of the road while reducing the need for routing maintenance, leading to extended service life without increasing structural capacity.

Terminology

• Alignment (road) - Cross slope/Banking/Superelevation, horizontal and vertical curvature of a road.
• All-weather road - Unpaved road that is constructed of a material that does not create mud during rainfall.
• Bollard - Rigid posts that can be arranged in a line to close a road or path to vehicles above a certain width
• Byway - Highway over which the public have a right to travel for vehicular and other kinds of traffic, but which is used mainly as footpaths and bridleways
• Bypass Road that avoids or "bypasses" a built-up area, town, or village
• Bottleneck - Section of a road with a carrying capacity substantially below that of other sections of the same road
• Botts' dots - Non reflective raised pavement marker used on roads
• Cat's eye - reflective raised pavement marker used on roads
• Chicane - Sequence of tight serpentine curves (usually an S-shape curve or a bus stop) in a roadway
• Chipseal - Road surface composed of a thin layer of crushed stone 'chips' and asphalt emulsion. It seals the surface and protects it from weather, but provides no structural strength. It is cheaper than asphalt concrete or a concrete, in the U.S. it is usually only used on low volume rural roads
• Corniche - Road on the side of a cliff or mountain, with the ground rising on one side and falling away on the other
• Curb - Edge where a raised pavement/sidewalk/footpath, road median, or road shoulder meets an unraised street or other roadway.
• Curb extension - (or also kerb extension, bulb-out, nib, elephant ear, curb bulge and blister) Traffic calming measure, intended to slow the speed of traffic and increase driver awareness, particularly in built-up and residential neighborhoods.
• Fork - (literally "fork in the road") Type of intersection where a road splits
• Guard rail - Prevents vehicles from veering off the road into oncoming traffic, crashing against solid objects or falling from a road
• Green lane - (UK) Unsurfaced road, may be so infrequently used that vegetation colonises freely, hence 'green'. Many green lanes are ancient routes that have existed for millennia, similar to a Byway
• Interstate Highway System - United States System of Interstate and Defense Highways
• Median - On divided roads, including expressways, motorways, or autobahns, the central reservation (British English), median (North American English), median strip (North American English and Australian English), neutral ground [Louisiana English] or central nature strip (Australian English) is the area which separates opposing lanes of traffic
• Mountain pass - Lower point that allows easier access through a range of mountains
• Milestone - One of a series of numbered markers placed along a road at regular intervals, showing the distance to destinations.
• Pavement - The road regarded as a geoconstruction.
• Pedestrian crossing - Designated point on a road at which some means are employed to assist pedestrians wishing to cross safely
• Private highway - Highway owned and operated for profit by private industry
• Private road - Road owned and maintained by a private individual, organization, or company rather than by a government
• Public space - Place where anyone has a right to come without being excluded because of economic or social conditions
• Ranch road - U.S. road which serves to connect rural and agricultural areas to market towns
• Road number - Often assigned to a stretch of public roadway. The number chosen is often dependent on the type of road, with numbers differentiating between interstates, motorways, arterial thoroughfares, and so forth
• Road-traffic safety - Process to reduce the harm (deaths, injuries, and property damage) resulting from crashes of road vehicles traveling on public roads
• Roadworks - Part or all of the road has to be occupied for work or maintenance relating to the road
• Roughness - Deviations from a true planar pavement surface, which affects vehicle suspension deflection, dynamic loading, ride quality, surface drainage and winter operations. Roughness have wavelengths ranging from 500 mm up to some 40 m. The upper limit may be as high as 350 m when considering motion sickness aspects; motion sickness is generated by motion with down to 0.1 Hz frequency; in an ambulance car driving 35 m/s (126 km/h), waves with up to 350 m will excite motion sickness.
• Shoulder - Reserved area by the verge of a road, generally it is kept clear of all traffic
• State highway - Road numbered by the state, falling below numbered national highways (like U.S. Routes) in the hierarchy OR A road maintained by the state, including nationally-numbered highways
• Texture (roads) - Deviations from a true planar pavement surface, which affects the interaction between road and tire. Microtexture have wavelengths below 0.5 mm, Macrotexture below 50 mm and Megatexture below 500 mm.
• Traffic calming - Set of strategies used by urban planners and traffic engineers which aim to slow down or reduce traffic, thereby improving safety for pedestrians and bicyclists as well as improving the environment for residents
• Traffic light - also known as a traffic signal, stop light, stop-and-go lights, robot or semaphore, is a signaling device positioned at a road intersection, pedestrian crossing, or other location in order to assign right of way to different approaches to an intersection

See also

• Corpse roads
• Design Manual for Roads and Bridges
• Habitat fragmentation
• Inca road system
• Line source
• List of roads and highways
• List of OECD countries by road network size

• Road movie
• Roadway air dispersion model
• Roadway noise
• Street
• Strip road
• Towing
• Trade route

References

External links

• The Post-Roads of Europe 1781 Map
• National Alliance Against Tolls
• The Roadex project