Road

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A road goes up a mountainside using hairpin turns in the French Alps.

A road is an identifiable route, way or path between two or more places.^[1] Roads are typically smoothed, paved, or otherwise prepared to allow easy travel;^[2] though they need not be, and historically many roads were simply recognizable routes without any formal construction or maintenance^[3]. 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.^[4] 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. ^[5]

[edit] Usage and etymology

See also: Usage of the terms railroad and railway and Ship transport

Misty road in Australia, entering into a township.

In original usage, a "road" was simply any pathway fit for riding. The word “street,” whose origin is the Latin strata, was kept for paved pathways that had been prepared to ease travel in some way. Thus, many "Roman Roads" have the word "street" as part of their name.^[6][7]

However, modern usage does not usually make this distinction^{[citation needed]} and it is only important since place names often hold the earlier usage in them; these days, roads are also prepared in some way^{[citation needed]}. This includes, at the least, the removal of trees and smoothing of the ground. In some dialects, lower grade roads are called trails^{[citation needed]} and tracks^{[citation needed]}and it is uncertain where "road" begins and trail ends^{[citation needed]}. Roads are a prerequisite for road transport of goods on wheeled vehicles^[6].

The word “road” emphasizes its function of transportation along its length,^{[citation needed]} while a “street” may be considered to have activity and commerce taking place on it (see street life)^{[citation needed]}.

[edit] History

See also: History of road transport

A cobblestone Roman road in Pompeii.

That the first pathways were the trails made animals has not been universally accepted, arguing that animals do not follow constant paths. ^[3] others argue that some roads originated from humans following migrating animals.^{[citation needed]} By about 10,000 BC, rough pathways were used by human travelers. ^[3]

Street paving has been found from around 4000 BC

• Stone Paved in the city of Ur in the Middle East 4000 BC ^[3]
• Made of Corduroy in Glastonbury, England 4000 BC ^[3]
• 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. ^[8][6]
• Brick paving in India as early as 3000 BC ^[3]
• In cities of the Indus Valley Civilization on the Indian subcontinent, such as Harrapa and Mohenjo-daro.^{[citation needed]}

The ancient Egyptians constructed a stone paved road to help move materials for the building of the Great Pyramid in about 3000 BC.^{[citation needed]}

The ancient Chinese constructed an extensive system of roads, some paved, from about 1100 BC onwards.^{[citation needed]} By 20 AD, the Chinese road network extended over 40,000 kilometres.^{[citation needed]}

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.^{[citation needed]} The road was used even after the Roman times. Because of the road's superior quality, mail couriers could travel 2,699 km in seven days.^{[citation needed]}

The Incas built fine highways, the Inca road system, for couriers through the Andes, and the Mayans built an extensive network of paved roads in Mexico before the European discovery of the New World.^{[citation needed]}

In ancient times, transport by river was far easier and faster than transport by road,^[6] especially considering the cost of road construction and the difference in carrying capacity between carts and river barges.^{[citation needed]} A hybrid of road transport and ship transport is the horse-drawn boat in which the horse follows a cleared path along the river bank.^{[citation needed]}

From about 312 BC, the Roman Empire built straight strong stone Roman roads throughout Europe and North Africa,^{[citation needed]} in support of its military campaigns. At it's 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. ^[6]

Road construction and maintenance in Britain was traditionally done on a local parish basis.^[6] This resulted in a poor and variable state of roads.^{[citation needed]} To remedy this, the first of the 'Turnpike Trusts' 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.^[6] The Rebecca Riots in Carmarthenshire from 1839 onwards contributed to having a Royal Commission and the demise of the system in 1844.^{[citation needed]}

Engineered roads in the age of horse-drawn transport aimed for a maximum gradient of 1 in 30 on a macadamized surface, since this was the steepest a horse could exert to pull a load up hill, which it could manage easily on the flat.^{[citation needed]} Notable road engineers from this period are Pierre Marie Jérôme Trésaguet (1716-1796) in France and John Loudon McAdam (1756-1836) in Scotland.

During the industrial revolution, the railway developed as a solution to the problem of rutting of the road surface by heavy carts. Instead of trying to build a strong surface across the whole road, the cart was constrained to run either on rails or grooves which could be made of much stronger, wear resistant material.^{[citation needed]}

Today, roads are almost exclusively built to enable travel by automobile and other wheeled vehicles.^{[citation needed]} In most countries, road transport is the most utilized way to move goods.^{[citation needed]} Also, in most developed countries, roads are formally divided into lanes to ensure the safe and smooth movement of traffic.^{[citation needed]}

[edit] Road transport policy

Road building and maintenance is an area of economic activity (compare military spending) that remains dominated by the public sector (though often through private contractors).^{[citation needed]} Roads (except those on private property not accessible to the general public) are typically paid for by taxes (often raised through levies on fuel),^{[citation needed]} though some public roads, especially highways are funded by tolls.^{[citation needed]} Yet, road building is inversely related to road maintenance, especially in nations with margined private sector.^{[citation needed]}

This section is a stub. You can help by expanding it.

[edit] Driving on the right or the left

Main article: Driving on the left or right.

In India, driving is on the left side of the road.

Traffic flows on the right or on the left side of the road depending on the country.^[9] 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.^{[citation needed]} In countries where traffic flows on the left, the reverse is true.

Traffic flow and road design in both cases are each other's mirror image.^{[citation needed]}

[edit] Planning and design

Road design consists of two important technical aspects:

• geometrical road design
• structural road design

Besides these two technical sides of the design, environmental issues, planning issues and juridical issues are important.

See: traffic

This section is a stub. You can help by expanding it.

[edit] Construction

The DN7 road near Sibiu, Romania.

Road in France

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.^{[citation needed]} Removal of earth and rock by digging or blasting, construction of embankments, bridges and tunnels, and removal of vegetation (this may involve deforestation) are often needed.^{[citation needed]} A variety of road building equipment is employed in road building.^{[citation needed]}

Once these activities are completed, construction of the pavement can begin.^{[citation needed]}

Firstly the longitudinal and vertical alignment of the road is set out by a surveyor. The alignment of the road will be marked with control pegs. The pegs will have level markings as a control mechanism to ensure the road is constructed to the appropriate design levels.^{[citation needed]}

Construction of the road commences with the stripping of the topsoil, within the road reserve. The topsoil is usually stockpiled nearby for rehabilitation of newly constructed embankments along the road.^{[citation needed]} The in-situ ground will be removed, using a heavy motorised grader to a level specified by the civil engineer.^{[citation needed]} This is considered as the road-bed level. It will be compacted using a heavy vibratory road roller.^{[citation needed]} Once the road-bed has been compacted to the required density (as will be specified by the engineer), the pavement layers can now be imported.^{[citation needed]}

If the subgrade can not be compacted to a suitable density as in a swamp, geotextile fabric can be used to maintain soil separation as engineered layers are added.^{[citation needed]} Minimium Two feet of soil are required to achieve the geo-technical effect.^{[citation needed]} The bearing capacity of geotechnical fabric and two feet of soil is equivilant to four feet of soil.^{[citation needed]} Load forces are distributed wider as roadbed thickness increases. Soft soils typically have a bearing capacity under 5 psi.^{[citation needed]}

The first layer to be imported is the selected sub-grade (SSG). This is usually a gravel type material.^{[citation needed]} Once placed the material is levelled off by a grader. It will be compacted to a required density, using a road roller.^{[citation needed]}

The next layer to be imported is the sub-base.^{[citation needed]} The sub-base material is of a higher quality than the selected sub-grade. Quality is defined as measurable physical characteristics. Durable stone, angular shape, gradation, water content define quality.^{[citation needed]} It is usually a gravel type material, with a high California Bearing Ratio (CBR). While the material is worked by a grader, water content is adjusted by drying or addition to achieve maximum soil density to aid compaction. The water content is optimal at maximum soil density. Moisture percent versus soil density follows a curve.^{[citation needed]} As water is added to dry soil the density increases until a water content is reached wherein added water will cause the water soil mix to become less dense. Density is related to the load bearing capacity. Therefore the maximum density will provide the maximum carrying capacity.^{[citation needed]} Once the sub-base layer has been compacted to its required density, the importation of the final layer can commence.

The final layer of a road is the base course consisting of gravel or crushed stone.^{[citation needed]} The base course will be leveled of and compacted. Sometimes (usually for roads that will experience heavy loads) portland cement will be added to it, to ensure adequate strength of this layer. On top of the base course is placed a surface course which typically consists of asphalt concrete or a seal considering of a mixture similar sized small stones, bitumen and portland cement.^{[citation needed]} This surface course strengthens the pavement structure by spreading out the vehicle loads applied to the subgrade.^{[citation needed]} It also provides a smooth and high-friction surface for vehicles to drive on.^{[citation needed]} The principal effect of the surface course is to provide a weather cap over the load bearing aggregate below.^{[citation needed]} Road failure is typically due to a failure of the subgrade or insufficient thickness of the road bed rather than the surface course.^{[citation needed]} Harmonic displacement can cause breaks in the road surface in a periodic repeating pattern.^{[citation needed]} The road dip and ridge pattern amplifies truck load impulse forces on the subgrade.^{[citation needed]}

Two important factors in road construction are ensuring adequate compaction of the pavement layers and ensuring quality control over the use of materials in the pavement layers.^{[citation needed]}

Each layer should be compacted such that the density of the layer is relatively close the maximum dry density of that specific material.^{[citation needed]} For road construction the density required is usually greater than 95% of the materials maximum dry density.^{[citation needed]} This limits the possibility of the pavement layers from settling and therefore preventing any undulations and holes in the road surface.

Materials used in the construction of roads should have a low Plasticity Index(PI). If the PI of the material is too high there may be a tendency for the material to swell which will cause numerous problems in the road surface.^{[citation needed]} The material should also have a high CBR, which will enable it to support the vehicular loads adequately. These factors are monitored constantly during construction.^{[citation needed]}

Modern roads, and indeed many ancient ones, such as those built by the Romans, feature a convex transverse profile known as superelevation or camber.^{[citation needed]} This is designed to allow water to drain away from the road to its edges. Water is then carried away by gutters to drains placed at intervals.^{[citation needed]} Some roads don't have gutters and water simply drains away to a naturally porous verge, or into ditches. Modern roads that carry motor traffic also employ camber in curves to aid traffic stability by allowing them to "bank into" the bend to some extent.^{[citation needed]}

On the side of the road there may be retroreflectors on pegs, rocks or crash barriers, white toward the direction of the traffic on that side of the road, and red toward the other direction.^{[citation needed]} In the road surface there may be cat's eyes: retroreflectors that protrude slightly, but which can be driven over without damage.^{[citation needed]}

Road signs are often also made retroreflective or even illuminated in rare circumstances.^{[citation needed]} For greater visibility of road signs at daytime, sometimes fluorescence is applied to get very bright colors.^{[citation needed]}

[edit] Maintenance

London Circuit, Canberra, Australia

A typical rural county road in Indiana, USA, where traffic flows on the right. The yellow lines indicate that passing is allowed in the ongoing direction but not in the oncoming direction.

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.^{[citation needed]} 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.^{[citation needed]} A typical tractor-trailer weighing 80,000 pounds with 8,000 pounds on the steer axle and 36,000 pounds on both of the tandem axle groups is expected to do 7,800 times more damage than a passenger vehicle with 2,000 pounds on each axle. In most pavement design methodologies trucks are considered to be the sole cause of pavement deterioration.^{[citation needed]}

Pavements are designed for an expected service life. Most European countries have strict standards for road construction that require that most roads should be able to go 30 years or longer between major resurfacings.^{[citation needed]} In the United States new pavements are typically designed for a service life of between 15 and 25 years, depending on the importance of the road.^{[citation needed]} Service life predictions are inherently unreliable due to the difficulty of predicting future traffic and environmental conditions.^{[citation needed]}

Virtually all roads require some form of maintenance before they come to the end of their service life. Maintenance activities can be divided into structural maintenance and functional maintenance, although there is a great deal of overlap.^{[citation needed]} Structural maintenance is maintenance intended to preserve the structural integrity of the pavement, and includes patching potholes, sealing cracks and overlays.^{[citation needed]} Functional maintenance is maintenance to improve the roadway's function of providing a smooth and safe surface for vehicles to drive on, and includes surface grinding and thin overlays.^{[citation needed]}

[edit] Heraldry

Somewhat unusually, in heraldry, a terrace or champagne (usually used as a depiction of a grassy "ground" at the bottom of a shield), or a compartment (a surface placed beneath the feet of supporters, figures holding up the shield, usually on either side) will be shown as crossed by a "road."^{[citation needed]}

[edit] Terminology

A sand road in Namibia

A typical rural gravel road in Indiana, USA.

A brick main street in Lebanon, Illinois

Wintery condition road in northern Sweden.

• All-weather road - an unpaved road that is constructed of material (particularly gravel) that does not create mud during rainfall.
• arterial road
• asphalt
• autobahn
• autoroute
• autostrasse
• bitumen
• bollard
• byway
• bypass
• bottleneck
• Botts' dots
• boulevard
• cat's eye
• chicane
• chipseal
• concrete
• Corduroy road
• corniche
• cul-de-sac
• curb
• curb extension
• dirt road
• divided highway
• expressway
• farm to market
• freeway
• fork (road)
• gravel road
• guard rail
• green lane
• hard shoulder
• highway
• Interchange
• Intersection
• Interstate Highway
• lane
• median
• mountain pass
• milestone
• motorway
• off-ramp
• on-ramp
• Parkway
• pavement
• pedestrian crossing
• performance
• plank road
• private highway
• private road
• public road
• public space
• ranch road
• range road
• ridge road
• road junction
• road number
• road safety
• road surface marking
• roadworks
• roundabout intersection
• rural route
• state highway
• street
• toll road
• traffic calming
• traffic circle
• traffic light
• traffic sign
• Unpaved road - a road without a bound surface layer (such as asphalt concrete or portland cement concrete). Types of unpaved roads include dirt roads and gravel roads. Unpaved roads are much cheaper to construct than paved roads, but may be more expensive to maintain especially when they have high traffic volumes. The cost of operating a vehicle on an unpaved road is also much higher than on a paved road.
• US highway
• winter road
• 2+1 road

[edit] See also

• Inca road system
• Line source
• List of roads and highways
• Logging roads
• Public road
• Road movie
• Roadway air dispersion model
• Roadway noise
• Towing
• Trade route
• Road safety

[edit] References

[edit] External links

Look up Road in
Wiktionary, the free dictionary.

Wikimedia Commons has media related to:

Road

• The Post-Roads of Europe 1781 Map