Learn more about Road
A road is an identifiable route 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 recognisable routes without any formal construction or maintenance. In urban areas roads may pass along and be named as streets, serving a dual function as urban space and route.
 Usage and etymology
In original usage, a "road" was simply any pathway fit for riding ("road" is cognate with "ride", e.g.: ships ride at anchor in roads). 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.
However, modern usage does not usually make this distinction and it is only important since place names often hold the earlier usage in them; these days, roads are also prepared in some way. This includes, at the least, the removal of trees and smoothing of the ground. In some dialects, lower grade roads are called trails and tracks and it is uncertain where "road" begins and trail ends. Roads are a prerequisite for road transport of goods on wheeled vehicles.
The word “road” emphasizes its function of transportation along its length, while a “street” may be considered to have activity and commerce taking place on it (see street life).
Street paving has been found from the first human settlements around 4000 BC see India's Indus Valley city Harrapa.
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 is the horse-drawn boat in which the horse follows a cleared path along the river bank.
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 was used even after the Roman times. Because of the road's superior quality, mail couriers could travel 2,699 km in seven days.
From about 300 BC, the Roman Empire built straight strong stone Roman roads throughout Europe and North Africa, in support of its military campaigns. By the 1st century the Roman Empire was connected by 85,000 kilometers of paved roads.
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' around 1706, to build good roads and collect tolls from passing vehicles. Eventually there were approximately 1,100 Trusts in Britain and some 38,000 km of engineered roads. The Rebecca Riots in Carmarthenshire from 1839 onwards contributed to having a Royal Commission and the demise of the system in 1844.
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. Notable road engineers from this period are Pierre Marie Jérôme Trésaguet (1716-1796) in France and John Loudon McAdam (1756-1836) in England.
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.
Today, roads are almost exclusively built to enable travel by automobile and other wheeled vehicles. In most countries, road transport is the most utilized way to move goods. Also, in most developed countries, roads are formally divided into lanes to ensure the safe and smooth movement of traffic.
 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). Roads (except those on private property 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.
 Driving on the right or the left
- Main article: Driving on the left or right.
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.
Traffic flow and road design in both cases are each other's mirror image.
Road design consists of two important technical aspects:
Besides these two technical sides of the design, environmental issues, planning issues and juridical issues are important.
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. 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. A variety of road building equipment is employed in road building.
Once these activities are completed, construction of the pavement can begin.
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.
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. The in-situ ground will be removed, using a heavy motorised grader to a level specified by the civil engineer. This is considered as the road-bed level. It will be compacted using a heavy vibratory road roller. 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.
The first layer to be imported is the selected sub-grade (SSG). This is usually a gravel type material. Once placed the material is levelled off by a grader. It will be compacted to a required density, using a road roller.
The next layer to be imported is the sub-base. The sub-base material is of a higher quality than the selected sub-grade. It is usually a gravel type material, with a high California Bearing Ratio (CBR). While the material is worked by a grader, it is mixed with water to aid compaction. 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. 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. This surface course strengthens the pavement structure by spreading out the vehicle loads applied to the subgrade. It also provides a smooth and high-friction surface for vehicles to drive on.
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.
Each layer should be compacted such that the density of the layer is relatively close the maximum dry density of that specific material. For road construction the density required is usually greater than 95% of the materials maximum dry density. 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 Plastcity Index(PI). If the PI of the material is too high there may be a tendancy for the material to swell which will cause numerous problems in the road surface. 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.
Modern roads, and indeed many ancient ones, such as those built by the Romans, feature a convex transverse profile known as superelevation or camber. 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. 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.
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. In the road surface there may be cat's eyes: retroreflectors that protrude slightly, but which can be driven over without damage.
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 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.
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. 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. Service life predictions are inherently unreliable due to the difficulty of predicting future traffic and environmental conditions.
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. Structural maintenance is maintenance intended to preserve the structural integrity of the pavement, and includes patching potholes, sealing cracks and overlays. 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.
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."
- All-weather road - an unpaved road that is constructed of material (particularly gravel) that does not create mud during rainfall.
- arterial road
- cat's eye
- corduroy road
- curb extension
- dirt road
- divided highway
- farm to market
- gravel road
- guard rail
- green lane
- hard shoulder
- Interstate Highway
- mountain pass
- pedestrian crossing
- 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
- roundabout intersection
- rural route
- state highway
- 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
 See also
- Inca road system
- Line source
- List of roads and highways
- Logging roads
- Public road
- Road movie
- Roadway air dispersion model
- Roadway noise
- Trade route
- Road safety
- Category:Anti-road protest
- Lay MG, Ways of the world. Rutgers University Press, New Brunswick, New Jersey, (1992). ISBN 0-8135-1758-3 .
 External links
- List of countries where traffic drives on the left, as well as historical background.
- Which side of the road do they drive on?
- Kansas State University Department of Civil Engineering - History of Concrete Road Building (PDF file)
- The Post-Roads of Europe 1781 Map
- EU road transport policybg:Път
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