Road
Overview
A road is a thoroughfare
Thoroughfare
A thoroughfare is a place of transportation intended to connect one location to another. Highways, roads, and trails are examples of thoroughfares used by a variety of general traffic. On land a thoroughfare may refer to anything from a rough trail to multi-lane highway with grade separated...

, route, or way on land between two places
Location (geography)
The terms location and place in geography are used to identify a point or an area on the Earth's surface or elsewhere. The term 'location' generally implies a higher degree of can certainty than "place" which often has an ambiguous boundary relying more on human/social attributes of place identity...

, which typically has been paved
Pavement (material)
Road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past cobblestones and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete. Such...

 or otherwise improved to allow travel by some conveyance, including a horse, cart, or motor vehicle
Motor vehicle
A motor vehicle or road vehicle is a self-propelled wheeled vehicle that does not operate on rails, such as trains or trolleys. The vehicle propulsion is provided by an engine or motor, usually by an internal combustion engine, or an electric motor, or some combination of the two, such as hybrid...

. Roads consist of one, or sometimes two, roadways (British English
British English
British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...

: carriageways) each with one or more lane
Lane
A lane is a part of the roadway within a road marked out for use by a single line of vehicles in such a way as to control and guide drivers for the purpose of reducing traffic conflicts. Most public roads have at least two lanes, one for traffic in each direction, separated by Lane markings...

s and also any associated sidewalk
Sidewalk
A sidewalk, or pavement, footpath, footway, and sometimes platform, is a path along the side of a road. A sidewalk may accommodate moderate changes in grade and is normally separated from the vehicular section by a curb...

s (British English: pavement) and road verges. Roads that are available for use by the public may be referred to as public roads or highway
Highway
A highway is any public road. In American English, the term is common and almost always designates major roads. In British English, the term designates any road open to the public. Any interconnected set of highways can be variously referred to as a "highway system", a "highway network", or a...

s
.
For purposes of international statistical
Statistics
Statistics is the study of the collection, organization, analysis, and interpretation of data. It deals with all aspects of this, including the planning of data collection in terms of the design of surveys and experiments....

 comparison, the OECD defines a road as "a line of communication (travelled way) using a stabilized base other than rails or air strips open to public traffic, primarily for the use of road motor vehicles running on their own wheels," which includes "bridges, tunnels, supporting structures, junctions, crossings, interchanges, and toll roads, but not cycle paths." In urban area
Urban area
An urban area is characterized by higher population density and vast human features in comparison to areas surrounding it. Urban areas may be cities, towns or conurbations, but the term is not commonly extended to rural settlements such as villages and hamlets.Urban areas are created and further...

s roads may diverge through a city
City
A city is a relatively large and permanent settlement. Although there is no agreement on how a city is distinguished from a town within general English language meanings, many cities have a particular administrative, legal, or historical status based on local law.For example, in the U.S...

 or village
Village
A village is a clustered human settlement or community, larger than a hamlet with the population ranging from a few hundred to a few thousand , Though often located in rural areas, the term urban village is also applied to certain urban neighbourhoods, such as the West Village in Manhattan, New...

 and be named as street
Street
A street is a paved public thoroughfare in a built environment. It is a public parcel of land adjoining buildings in an urban context, on which people may freely assemble, interact, and move about. A street can be as simple as a level patch of dirt, but is more often paved with a hard, durable...

s, serving a dual function as urban space easement
Easement
An easement is a certain right to use the real property of another without possessing it.Easements are helpful for providing pathways across two or more pieces of property or allowing an individual to fish in a privately owned pond...

 and route. Modern roads are normally smoothed, paved
Pavement (material)
Road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past cobblestones and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete. Such...

, or otherwise prepared to allow easy travel
Travel
Travel is the movement of people or objects between relatively distant geographical locations. 'Travel' can also include relatively short stays between successive movements.-Etymology:...

. Historically many roads were simply recognizable routes without any formal construction or maintenance.
In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, laws distinguish between public roads, which are open to public use, and private roads, which are privately controlled.
In the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 there is some ambiguity between the terms highway and road.
Encyclopedia
A road is a thoroughfare
Thoroughfare
A thoroughfare is a place of transportation intended to connect one location to another. Highways, roads, and trails are examples of thoroughfares used by a variety of general traffic. On land a thoroughfare may refer to anything from a rough trail to multi-lane highway with grade separated...

, route, or way on land between two places
Location (geography)
The terms location and place in geography are used to identify a point or an area on the Earth's surface or elsewhere. The term 'location' generally implies a higher degree of can certainty than "place" which often has an ambiguous boundary relying more on human/social attributes of place identity...

, which typically has been paved
Pavement (material)
Road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past cobblestones and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete. Such...

 or otherwise improved to allow travel by some conveyance, including a horse, cart, or motor vehicle
Motor vehicle
A motor vehicle or road vehicle is a self-propelled wheeled vehicle that does not operate on rails, such as trains or trolleys. The vehicle propulsion is provided by an engine or motor, usually by an internal combustion engine, or an electric motor, or some combination of the two, such as hybrid...

. Roads consist of one, or sometimes two, roadways (British English
British English
British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...

: carriageways) each with one or more lane
Lane
A lane is a part of the roadway within a road marked out for use by a single line of vehicles in such a way as to control and guide drivers for the purpose of reducing traffic conflicts. Most public roads have at least two lanes, one for traffic in each direction, separated by Lane markings...

s and also any associated sidewalk
Sidewalk
A sidewalk, or pavement, footpath, footway, and sometimes platform, is a path along the side of a road. A sidewalk may accommodate moderate changes in grade and is normally separated from the vehicular section by a curb...

s (British English: pavement) and road verges. Roads that are available for use by the public may be referred to as public roads or highway
Highway
A highway is any public road. In American English, the term is common and almost always designates major roads. In British English, the term designates any road open to the public. Any interconnected set of highways can be variously referred to as a "highway system", a "highway network", or a...

s
.

Definitions

For purposes of international statistical
Statistics
Statistics is the study of the collection, organization, analysis, and interpretation of data. It deals with all aspects of this, including the planning of data collection in terms of the design of surveys and experiments....

 comparison, the OECD defines a road as "a line of communication (travelled way) using a stabilized base other than rails or air strips open to public traffic, primarily for the use of road motor vehicles running on their own wheels," which includes "bridges, tunnels, supporting structures, junctions, crossings, interchanges, and toll roads, but not cycle paths." In urban area
Urban area
An urban area is characterized by higher population density and vast human features in comparison to areas surrounding it. Urban areas may be cities, towns or conurbations, but the term is not commonly extended to rural settlements such as villages and hamlets.Urban areas are created and further...

s roads may diverge through a city
City
A city is a relatively large and permanent settlement. Although there is no agreement on how a city is distinguished from a town within general English language meanings, many cities have a particular administrative, legal, or historical status based on local law.For example, in the U.S...

 or village
Village
A village is a clustered human settlement or community, larger than a hamlet with the population ranging from a few hundred to a few thousand , Though often located in rural areas, the term urban village is also applied to certain urban neighbourhoods, such as the West Village in Manhattan, New...

 and be named as street
Street
A street is a paved public thoroughfare in a built environment. It is a public parcel of land adjoining buildings in an urban context, on which people may freely assemble, interact, and move about. A street can be as simple as a level patch of dirt, but is more often paved with a hard, durable...

s, serving a dual function as urban space easement
Easement
An easement is a certain right to use the real property of another without possessing it.Easements are helpful for providing pathways across two or more pieces of property or allowing an individual to fish in a privately owned pond...

 and route. Modern roads are normally smoothed, paved
Pavement (material)
Road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past cobblestones and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete. Such...

, or otherwise prepared to allow easy travel
Travel
Travel is the movement of people or objects between relatively distant geographical locations. 'Travel' can also include relatively short stays between successive movements.-Etymology:...

. Historically many roads were simply recognizable routes without any formal construction or maintenance.

United States

In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, laws distinguish between public roads, which are open to public use, and private roads, which are privately controlled.

United Kingdom

In the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 there is some ambiguity between the terms highway and road. The Highway code
Highway Code
The Highway Code is the official road user guide for Great Britain. In Northern Ireland the applies while the Republic of Ireland has its own Rules of the Road. It contains 306 numbered rules and 9 annexes covering pedestrians, animals, cyclists, motorcyclists and drivers...

 details rules for "road users". For the purposes of the English law
English law
English law is the legal system of England and Wales, and is the basis of common law legal systems used in most Commonwealth countries and the United States except Louisiana...

, Highways Act 1980
Highways Act 1980
The Highways Act 1980 is an Act of the Parliament of the United Kingdom dealing with the management and operation of the road network in England and Wales. It consolidated with amendments several earlier pieces of legislation. Many amendments relate only to changes of highway authority, to include...

, which covers England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

 and Wales
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

 but not Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

 or Northern Ireland
Northern Ireland
Northern Ireland is one of the four countries of the United Kingdom. Situated in the north-east of the island of Ireland, it shares a border with the Republic of Ireland to the south and west...

, the term road is defined to be "any length of highway or of any other road to which the public has access, and includes bridges over which a road passes." This includes footpath
Footpath
A Footpath is a thoroughfare intended for by pedestrians but not by motorized vehicles. The term is often for paths within an urban area that offer shorter quieter routes for pedestrians, they may also provide access to the surrounding countryside or parks...

s, bridleways and cycle tracks, and also road and driveways on private land and many car parks. Vehicle Excise Duty
Vehicle excise duty
Vehicle Excise Duty is a vehicle road use tax levied as an excise duty which must be paid for most types of vehicle which are to be used on the public roads in the United Kingdom...

, a road use tax
Road tax
Road tax, known by various names around the world, is a tax which has to be paid on a motor vehicle before using it on a public road.-Australia:...

, is payable on some vehicles used on the public road.

The definition of a road depends on the definition of a highway, however there is no formal definition for a highway in the relevant Act. A 1984 ruling said "the land over which a public right of way exists is known as a highway; and although most highways have been made up into roads, and most easements of way exist over footpaths, the presence or absence of a made road has nothing to do with the distinction. Another legal view is that while a highway historically included footpath
Footpath
A Footpath is a thoroughfare intended for by pedestrians but not by motorized vehicles. The term is often for paths within an urban area that offer shorter quieter routes for pedestrians, they may also provide access to the surrounding countryside or parks...

s, bridleways, driftways, etc., it can now be used to mean those ways that allow the movement of motor-vehicles, and the term rights of way can be used to cover the wider usage.

Historical road construction


The assertion that the first pathways were the trail
Trail
A trail is a path with a rough beaten or dirt/stone surface used for travel. Trails may be for use only by walkers and in some places are the main access route to remote settlements...

s made by animals has not been universally accepted, since in many cases animals do not follow constant paths. Others believe that some roads originated from following animal trails. The Icknield Way
Icknield Way
The Icknield Way is an ancient trackway in southern England. It follows the chalk escarpment that includes the Berkshire Downs and Chiltern Hills.-Background:...

 is given as an example of this type of road origination, where man and animal both selected the same natural line. By about 10,000 BC, rough pathways were used by human travelers.
  • Stone
    Cobblestone
    Cobblestones are stones that were frequently used in the pavement of early streets. "Cobblestone" is derived from the very old English word "cob", which had a wide range of meanings, one of which was "rounded lump" with overtones of large size...

    -paved
    Pavement (material)
    Road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past cobblestones and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete. Such...

     streets are found in the city of Ur
    Ur
    Ur was an important city-state in ancient Sumer located at the site of modern Tell el-Muqayyar in Iraq's Dhi Qar Governorate...

     in the Middle East
    Middle East
    The Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East...

     dating back to 4000 BC.

  • Corduroy roads (log roads)
    Corduroy road
    A corduroy road or log road is a type of road made by placing sand-covered logs perpendicular to the direction of the road over a low or swampy area....

     are found dating to 4000 BC in Glastonbury, England.

  • The timber trackway
    Timber trackway
    A timber trackway was typically used as the shortest route between two places in a bog or peatland and have been built for thousands of years as a means of getting between two points. Timber trackways have been identified in archaeological finds in Neolithic England, dating to 500 years before...

    ; Sweet Track
    Sweet Track
    The Sweet Track is an ancient causeway in the Somerset Levels, England. It was built in 3807 or 3806 BC and has been claimed to be the oldest road in the world. It was the oldest timber trackway discovered in Northern Europe until the 2009 discovery of a 6,000 year-old trackway in Belmarsh Prison...

     causeway
    Causeway
    In modern usage, a causeway is a road or railway elevated, usually across a broad body of water or wetland.- Etymology :When first used, the word appeared in a form such as “causey way” making clear its derivation from the earlier form “causey”. This word seems to have come from the same source by...

     in England
    England
    England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

    , is one of the oldest engineered roads discovered and the oldest timber trackway discovered in Northern Europe
    Northern Europe
    Northern Europe is the northern part or region of Europe. Northern Europe typically refers to the seven countries in the northern part of the European subcontinent which includes Denmark, Estonia, Latvia, Lithuania, Norway, Finland and Sweden...

    . Built in winter 3807 BC or spring 3806 BC, tree-ring dating (Dendrochronology)
    Dendrochronology
    Dendrochronology or tree-ring dating is the scientific method of dating based on the analysis of patterns of tree-rings. Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year...

     enabled very precise dating. It has been claimed to be the oldest road in the world.

  • Brick
    Brick
    A brick is a block of ceramic material used in masonry construction, usually laid using various kinds of mortar. It has been regarded as one of the longest lasting and strongest building materials used throughout history.-History:...

    -paved streets were used in India
    India
    India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

     as early as 3000 BC .

  • In 500 BC, Darius I the Great started an extensive road system for Persia (Iran
    Iran
    Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

    ), including the famous Royal Road
    Royal Road
    The Persian Royal Road was an ancient highway reorganized and rebuilt by the Persian king Darius the Great of the Achaemenid Empire in the 5th century BC. Darius built the road to facilitate rapid communication throughout his very large empire from Susa to Sardis...

    , which was one of the finest highways of its time. The road remained in use after Roman times.

  • In ancient times, transport by river
    River
    A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

     was far easier and faster than transport by road, especially considering the cost of road construction and the difference in carrying capacity between cart
    Cart
    A cart is a vehicle designed for transport, using two wheels and normally pulled by one or a pair of draught animals. A handcart is pulled or pushed by one or more people...

    s and river barge
    Barge
    A barge is a flat-bottomed boat, built mainly for river and canal transport of heavy goods. Some barges are not self-propelled and need to be towed by tugboats or pushed by towboats...

    s. A hybrid of road transport and ship transport beginning in about 1740 is the horse-drawn boat
    Horse-drawn boat
    A horse-drawn boat or tow-boat is a historic boat operating on a canal, pulled by a horse walking on a special road along the canal, the towpath.-United Kingdom:...

     in which the horse follows a cleared path along the river bank.

  • From about 312 BC, the Roman Empire
    Roman Empire
    The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

     built straight strong stone Roman road
    Roman road
    The Roman roads were a vital part of the development of the Roman state, from about 500 BC through the expansion during the Roman Republic and the Roman Empire. Roman roads enabled the Romans to move armies and trade goods and to communicate. The Roman road system spanned more than 400,000 km...

    s throughout Europe and North Africa
    North Africa
    North Africa or Northern Africa is the northernmost region of the African continent, linked by the Sahara to Sub-Saharan Africa. Geopolitically, the United Nations definition of Northern Africa includes eight countries or territories; Algeria, Egypt, Libya, Morocco, South Sudan, Sudan, Tunisia, and...

    , in support of its military campaigns. At its peak the Roman Empire was connected by 29 major roads moving out from Rome
    Rome
    Rome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...

     and covering 78,000 kilometers or 52,964 Roman miles of paved roads.

  • In the 8th century AD, many roads were built throughout the Arab Empire
    Caliphate
    The term caliphate, "dominion of a caliph " , refers to the first system of government established in Islam and represented the political unity of the Muslim Ummah...

    . The most sophisticated roads were those in Baghdad
    Baghdad
    Baghdad is the capital of Iraq, as well as the coterminous Baghdad Governorate. The population of Baghdad in 2011 is approximately 7,216,040...

    , Iraq
    Iraq
    Iraq ; officially the Republic of Iraq is a country in Western Asia spanning most of the northwestern end of the Zagros mountain range, the eastern part of the Syrian Desert and the northern part of the Arabian Desert....

    , which were paved with tar
    Tar
    Tar is modified pitch produced primarily from the wood and roots of pine by destructive distillation under pyrolysis. Production and trade in tar was a major contributor in the economies of Northern Europe and Colonial America. Its main use was in preserving wooden vessels against rot. The largest...

    . Tar was derived from petroleum
    Petroleum
    Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

    , accessed from oil field
    Oil field
    An oil field is a region with an abundance of oil wells extracting petroleum from below ground. Because the oil reservoirs typically extend over a large area, possibly several hundred kilometres across, full exploitation entails multiple wells scattered across the area...

    s in the region, through the chemical process of destructive distillation
    Destructive distillation
    Destructive distillation is the chemical process involving the decomposition of feedstock by heating to a high temperature; the term generally applies to processing of organic material in the absence of air or in the presence of limited amounts of oxygen or other reagents, catalysts, or solvents,...

    .

  • The Highways Act 1555
    Highways Act 1555
    The Highways Act 1555 , sometimes the First Statute of Highways, was an Act of Parliament of the Parliament of England passed in 1555...

     in Britain transferred responsibility for maintaining roads from government to local parishes. 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 (22,870 miles
    Miles
    Miles is the plural of mile.Miles may also refer to:- People :*Miles Brothers, American cinema pioneers* Miles ** Miles Browning, World War II admiral** Miles Davis, jazz trumpet player** Miles Austin, Dallas Cowboys wide receiver...

    ) of engineered roads. The Rebecca Riots
    Rebecca Riots
    The Rebecca Riots took place between 1839 and 1843 in South and Mid Wales. They were a series of protests undertaken by local farmers and agricultural workers in response to perceived unfair taxation. The rioters, often men dressed as women, took their actions against toll-gates, as they were...

     in Carmarthenshire
    Carmarthenshire
    Carmarthenshire is a unitary authority in the south west of Wales and one of thirteen historic counties. It is the 3rd largest in Wales. Its three largest towns are Llanelli, Carmarthen and Ammanford...

     and Rhayader
    Rhayader
    Rhayader is a market town and community in Powys, Mid Wales. It has a population of 2,075, and is the first town on the banks of the River Wye, from its source on the Plynlimon range of the Cambrian Mountains....

     from 1839 to 1844 contributed to a Royal Commission
    Royal Commission
    In Commonwealth realms and other monarchies a Royal Commission is a major ad-hoc formal public inquiry into a defined issue. They have been held in various countries such as the United Kingdom, Australia, Canada, New Zealand, and Saudi Arabia...

     that led to the demise of the system in 1844, which coincided with the development of the UK railway system
    History of rail transport in Great Britain to 1830
    The history of rail transport in Great Britain to 1830 covers the period up to the opening of the Liverpool and Manchester Railway, the world's first intercity passenger railway operated solely by steam locomotives. The earliest form of railways, horse-drawn wagonways, originated in Germany in the...

    .

Design

Structural road design
Structural road design
Structural road design aims to ensure the road is strong enough for the expected number of vehicles in a certain number of years. The input of a calculation is the number expected of vehicles divided in groups and the number of years that the road has to function before the road structure has to...

 is the science of designing a road for its environment in order to extend its longevity and reduce maintenance. The Shell pavement design method is used in many countries for the design of new asphalt roads.

Construction

Road construction requires the creation of a continuous right-of-way, overcoming geographic obstacles and having grades low enough to permit vehicle
Vehicle
A vehicle is a device that is designed or used to transport people or cargo. Most often vehicles are manufactured, such as bicycles, cars, motorcycles, trains, ships, boats, and aircraft....

 or foot travel
Walking
Walking is one of the main gaits of locomotion among legged animals, and is typically slower than running and other gaits. Walking is defined by an 'inverted pendulum' gait in which the body vaults over the stiff limb or limbs with each step...

. (pg15) and may be required to meet standards set by law
Law
Law is a system of rules and guidelines which are enforced through social institutions to govern behavior, wherever possible. It shapes politics, economics and society in numerous ways and serves as a social mediator of relations between people. Contract law regulates everything from buying a bus...

or official guidelines. The process is often begun with the removal of earth and rock by digging or blasting, construction of embankments
Embankment (transportation)
To keep a road or railway line straight or flat, and where the comparative cost or practicality of alternate solutions is prohibitive, the land over which the road or rail line will travel is built up to form an embankment. An embankment is therefore in some sense the opposite of a cutting, and...

, bridge
Bridge
A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle...

s and tunnels, and removal of vegetation (this may involve deforestation
Deforestation
Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a nonforest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use....

) and followed by the laying of pavement material
Pavement (material)
Road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past cobblestones and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete. Such...

. A variety of road building equipment is employed in road building.


After design
Structural road design
Structural road design aims to ensure the road is strong enough for the expected number of vehicles in a certain number of years. The input of a calculation is the number expected of vehicles divided in groups and the number of years that the road has to function before the road structure has to...

, approval
Approval rating
In the United States, presidential job approval ratings were introduced by George Gallup in the late 1930s to gauge public support for the President of the United States during his term. An approval rating is a percentage determined by a polling which indicates the percentage of respondents to an...

, planning
Planning
Planning in organizations and public policy is both the organizational process of creating and maintaining a plan; and the psychological process of thinking about the activities required to create a desired goal on some scale. As such, it is a fundamental property of intelligent behavior...

, legal and environmental
Environmental policy
Environmental policy is any [course of] action deliberately taken [or not taken] to manage human activities with a view to prevent, reduce, or mitigate harmful effects on nature and natural resources, and ensuring that man-made changes to the environment do not have harmful effects on...

 considerations have been addressed alignment of the road is set out by a surveyor
Surveying
See Also: Public Land Survey SystemSurveying or land surveying is the technique, profession, and science of accurately determining the terrestrial or three-dimensional position of points and the distances and angles between them...

. The Radii
Radius of curvature (mathematics)
In geometry, the radius of curvature, R, of a curve at a point is a measure of the radius of the circular arc which best approximates the curve at that point. If this value taken to be positive when the curve turns anticlockwise and negative when the curve turns clockwise...

 and gradient
Slope
In mathematics, the slope or gradient of a line describes its steepness, incline, or grade. A higher slope value indicates a steeper incline....

 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
Benchmark (surveying)
The term bench mark, or benchmark, originates from the chiseled horizontal marks that surveyors made in stone structures, into which an angle-iron could be placed to form a "bench" for a leveling rod, thus ensuring that a leveling rod could be accurately repositioned in the same place in the future...

  (page59)

Roads are designed and built for primary use by vehicular and pedestrian
Pedestrian
A pedestrian is a person traveling on foot, whether walking or running. In some communities, those traveling using roller skates or skateboards are also considered to be pedestrians. In modern times, the term mostly refers to someone walking on a road or footpath, but this was not the case...

 traffic
Traffic
Traffic on roads may consist of pedestrians, ridden or herded animals, vehicles, streetcars and other conveyances, either singly or together, while using the public way for purposes of travel...

. Storm drain
Storm drain
A storm drain, storm sewer , stormwater drain or drainage well system or simply a drain or drain system is designed to drain excess rain and ground water from paved streets, parking lots, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems...

age and environmental considerations are a major concern. Erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...

 and sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

 controls are constructed to prevent detrimental effects. Drainage lines are laid with sealed
Seal (mechanical)
A mechanical seal is a device which helps join systems or mechanisms together by preventing leakage , containing pressure, or excluding contamination...

 joints in the road easement
Easement
An easement is a certain right to use the real property of another without possessing it.Easements are helpful for providing pathways across two or more pieces of property or allowing an individual to fish in a privately owned pond...

 with runoff coefficient
Coefficient
In mathematics, a coefficient is a multiplicative factor in some term of an expression ; it is usually a number, but in any case does not involve any variables of the expression...

s and characteristics adequate for the land zoning
Zoning
Zoning is a device of land use planning used by local governments in most developed countries. The word is derived from the practice of designating permitted uses of land based on mapped zones which separate one set of land uses from another...

 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
Watercourse
A watercourse is any flowing body of water. These include rivers, streams, anabranches, and so forth.-See also:* physical geography* Environmental flow* Waterway* Hydrology* Wadi-External links:...

, creek
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...

, river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 or the sea
Sea
A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...

 for drainage discharge. (page38 to 40)

A borrow pit
Borrow pit
A borrow pit, also known as a sand box, is a term used in construction and civil engineering. It describes an area where material has been dug for use at another location. Borrow pits can be found close to many major construction projects...

 (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
Water well
A water well is an excavation or structure created in the ground by digging, driving, boring or drilling to access groundwater in underground aquifers. The well water is drawn by an electric submersible pump, a trash pump, a vertical turbine pump, a handpump or a mechanical pump...

 or for working (crushing and screening)
Gravel
Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...

 of materials for construction needs. The top soil and vegetation
Vegetation
Vegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader...

 is removed from the borrow pit and stockpiled for subsequent rehabilitation
Land rehabilitation
Land rehabilitation is the process of returning the land in a given area to some degree of its former state, after some process has resulted in its damage...

 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. Tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...

s 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
Topsoil
Topsoil is the upper, outermost layer of soil, usually the top to . It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs.-Importance:...

 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
Fill dirt
Fill dirt is earthy material which is used to fill in a depression or hole in the ground or create mounds or otherwise artificially change the grade or elevation of real property....

 should be free of organics
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

, meet minimum California bearing ratio
California Bearing Ratio
The California bearing ratio is a penetration test for evaluation of the mechanical strength of road subgrades and basecourses. It was developed by the California Department of Transportation before World War II....

 (CBR) results and have a low plasticity index. The lower fill generally comprises sand or a sand-rich mixture with fine gravel, which acts as an inhibitor to the growth of plants or other vegetable matter. The compacted fill also serves as lower-stratum drainage. Select second fill (sieve
Sieve
A sieve, or sifter, separates wanted elements from unwanted material using a woven screen such as a mesh or net. However, in cooking, especially with flour, a sifter is used to aerate the substance, among other things. A strainer is a type of sieve typically used to separate a solid from a liquid...

d) should be composed of gravel
Gravel
Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...

, decomposed rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

 or broken rock below a specified Particle size and be free of large lumps of clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

. Sand clay
Loam
Loam is soil composed of sand, silt, and clay in relatively even concentration . Loam soils generally contain more nutrients and humus than sandy soils, have better infiltration and drainage than silty soils, and are easier to till than clay soils...

 fill may also be used. The road bed must be "proof rolled" after each layer of fill is compacted. If a roller
Road roller
A road roller is a compactor type engineering vehicle used to compact soil, gravel, concrete, or asphalt in the construction of roads and foundations, similar rollers are used also at landfills or in agriculture.In some parts of the world, road rollers are still known colloquially as steam...

 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
Pavement (material)
Road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past cobblestones and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete. Such...

 or left with a gravel or other natural
Dirt road
Dirt road is a common term for an unpaved road made from the native material of the land surface through which it passes, known to highway engineers as subgrade material. Dirt roads are suitable for vehicles; a narrower path for pedestrians, animals, and possibly small vehicles would be called a...

 surface. The type of road
Types of road
Many types of road exist around the world, all of which are thoroughfares which can be used by motorized traffic. Roads are not necessarily available for use by the general public without permission, highways are available for by the public, although a toll may be charged...

 surface is dependent on economic factors and expected usage. Safety
Road-traffic safety
The term road traffic safety is about the risk of a person being killed or seriously injured while using the road network as a pedestrian, cyclist, motorist or user of on road public transport...

 improvements like Traffic sign
Traffic sign
Traffic signs or road signs are signs erected at the side of roads to provide information to road users. With traffic volumes increasing over the last eight decades, many countries have adopted pictorial signs or otherwise simplified and standardized their signs to facilitate international travel...

s, Crash barriers, Raised pavement marker
Raised pavement marker
A raised pavement marker is a safety device used on roads. These devices are usually made with plastic, ceramic, or occasionally metal, and come in a variety of shapes and colors. Many varieties include a lens or sheeting that enhance their visibility by reflecting automotive headlights...

s, and other forms of Road surface marking
Road surface marking
Road surface marking is any kind of device or material that is used on a road surface in order to convey official information. They can also be applied in other facilities used by vehicles to mark parking spaces or designate areas for other uses....

 are installed.

According to a May 2009 report by the American Association of State Highway and Transportation Officials (AASHTO) and TRIP—a national transportation research organization—driving on rough roads costs the average American motorist approximately $400 a year in extra vehicle operating costs. Drivers living in urban areas with populations more than 250,000 are paying upwards of $750 more annually because of accelerated vehicle deterioration, increased maintenance, additional fuel consumption, and tire wear caused by poor road conditions.

When a single carriageway
Single carriageway
A single carriageway is a road with 1, 2 or more lanes arranged within a single carriageway with no central reservation to separate opposing flows of traffic. Two-lane road or two-lane highway are single carriageway with one lane for each direction...

 road is converted into dual carriageway
Dual carriageway
A dual carriageway is a class of highway with two carriageways for traffic travelling in opposite directions separated by a central reservation...

 by building a second separate carriageway alongside the first, it is usually referred to as duplication, twinning or doubling. 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
Single track (rail)
A single track railway is where trains in both directions share the same track. Single track is normally used on lesser used rail lines, often branch lines, where the traffic density is not high enough to justify the cost of building double tracks....

 to double track
Double track
A double track railway usually involves running one track in each direction, compared to a single track railway where trains in both directions share the same track.- Overview :...

, 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
AASHO Road Test
The AASHO Road Test was a series of experiments carried out by the American Association of State Highway and Transportation Officials to determine how traffic contributed to the deterioration of highway pavements...

, it was empirically determined that the effective damage done to the road is roughly proportional to the Fourth power
Fourth power
In arithmetic and algebra, the fourth power of a number n is the result of multiplying n by itself four times. So:Fourth powers are also formed by multiplying a number by its cube...

 of axle weight
Gross axle weight rating
The gross axle weight rating is the maximum distributed weight that may be supported by an axle of a road vehicle. Typically, GAWR is followed by either the letters FR or RR, which indicate front or rear axles respectively.-Importance:...

. A typical tractor-trailer
Semi-trailer truck
A semi-trailer truck, also known as a semi, tractor-trailer, or articulated truck or articulated lorry, is an articulated vehicle consisting of a towing engine , and a semi-trailer A semi-trailer truck, also known as a semi, tractor-trailer, or (in the United Kingdom and Ireland) articulated truck...

 weighing 80,000 pounds
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...

 (36.287 t
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...

) with 8,000 pounds (3.629 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
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

 with 2,000 pounds (0.907 t) on each axle. Pothole
Pothole
A pothole is a type of disruption in the surface of a roadway where a portion of the road material has broken away, leaving a hole.- Formation :...

s on roads are caused by rain damage and vehicle braking or related construction works.

Pavements are designed for an expected service life
Service life
A product's service life is its expected lifetime, or the acceptable period of use in service. It is the time that any manufactured item can be expected to be 'serviceable' or supported by its manufacturer....

 or design life
Design life
The design life of a component or product is the period of time during which the item is expected by its designers to work within its specified parameters; in other words, the life expectancy of the item...

. In some UK countries the standard design life is 40 years for new bitumen and concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

 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 than 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
Wacker Drive
Wacker Drive is a major street in Chicago, Illinois, United States, running along the south side of the main branch and the east side of the south branch of the Chicago River...

", 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 use pavement management
Pavement management
Pavement management is the process of overseeing the maintenance andrepair of a network of roadways. In effect, every highwaysuperintendent does pavement management. Pavement management incorporates life cycle costs into a more systematic approach to minor and major M&R projects...

 techniques to continually monitor road conditions and schedule preventive maintenance treatments as needed to prolong the lifespan of their roads. Technically advanced agencies monitor the road network surface condition with sophisticated equipment such as laser/inertial Profilometer
Profilometer
Profilometer is a measuring instrument used to measure a surface's profile, in order to quantify its roughness.While the historical notion of a profilometer was a device similar to a phonograph that measures a surface as the surface is moved relative to the contact profilometer's stylus, this...

s. These measurements include road curvature
Curvature
In mathematics, curvature refers to any of a number of loosely related concepts in different areas of geometry. Intuitively, curvature is the amount by which a geometric object deviates from being flat, or straight in the case of a line, but this is defined in different ways depending on the context...

, cross slope
Cross slope
Cross slope is a geometric feature of pavement surfaces; the transversal slope [%] with respect to the horizon. It is a very important safety factor. One task is to make water run off the surface to a drainage system, as Cross Slope is the main contributor to Pavement Drainage gradient. Very low...

, asperity, roughness, rutting and texture (roads)
Texture
Texture may refer to:* Textures , album of Brian Eno* Textures , a metal band from the Netherlands* Texture , theoretical topological defect in the structure of spacetime...

. This data is fed into a pavement management system
Pavement management system
Pavement management system or PMS is a term that relates to a system that utilizes the condition coding of roadways coupled with the identification of strategies to determine maintenance or re-construction activities...

, which recommends the best maintenance or construction treatment to correct the damage that has occurred.

Maintenance treatments for asphalt concrete
Asphalt concrete
Asphalt concrete is a composite material commonly used in construction projects such as road surfaces, airports and parking lots. It consists of asphalt and mineral aggregate mixed together, then laid down in layers and compacted...

 generally include crack sealing, surface rejuvenating, fog sealing, micro-milling and surface treatments
Chipseal
Chip seal is a pavement surface treatment that combines a layer of asphalt with a layer of fine aggregate. In the United States, chip seals are typically used on rural roads carrying lower traffic volumes, and the process is often referred to as "asphaltic surface treatment"...

. 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.

Failure to maintain roads properly can create significant costs to society, in a 2009 report released by the American Association of State Highway and Transportation Officials (USA) about 50% of the roads in the USA are in bad condition with urban areas worse. The report estimates that urban drivers pay an average of $746/year on vehicle repairs while the average US motorist pays about $335/year. In contrast, the average motorist pays about $171/year in road maintenance taxes (based on 600 gallons/year and $0.285/gallon tax).

Slab Stabilization

Distress and serviceability loss on concrete roads can be caused by loss of support due to voids beneath the concrete pavement slabs. The voids usually occur near cracks or joints due to surface water infiltration. The most common causes of voids are pumping, consolidation, subgrade failure and bridge approach failure. Slab stabilization is a non-destructive method of solving this problem and is usually employed with other Concrete Pavement Restoration (CPR)
International Grooving & Grinding Association
The International Grooving & Grinding Association is a non-profit trade association founded in 1972 that represents the industry that performs grooving and grinding of both concrete and asphalt surfaces in addition to Concrete Pavement Restoration and Concrete Pavement Preservation methods...

  methods including patching and diamond grinding. The technique restores support to concrete slabs by filing small voids that develop underneath the concrete slab at joints, cracks or the pavement edge. The process consists of pumping a cementitous grout or polyurethane mixture through holes drilled through the slab. The grout can fill small voids beneath the slab and/or sub-base. The grout also displaces free water and helps keep water from saturating and weakening support under the joints and slab edge after stabilization is complete. The three steps for this method after finding the voids are locating and drilling holes, grout injection and post-testing the stabilized slabs.

Slab stabilization does not correct depressions, increase the design structural capacity, stop erosion or eliminate faulting. It does, however, restore the slab support, therefore, decreasing deflections under the load. Stabilization should only be performed at joints and cracks where loss of support exists. Visual inspection is the simplest manner to find voids. Signs that repair is needed are transverse joint faulting, corner breaks and shoulder drop off and lines at or near joints and cracks. Deflection testing is another common procedure utilized to locate voids. It is recommended to do this testing at night as during cooler temperatures, joints open, aggregate interlock diminishes and load deflections are at their highest.

Testing

Ground penetrating radar pulses electromagnetic waves into the pavement and measures and graphically displays the reflected signal. This can reveal voids and other defects.

The epoxy/core test, detects voids by visual and mechanical methods. It consists of drilling a 25 to 50 millimeter hole through the pavement into the sub-base with a dry-bit roto-hammer. Next, a two-part epoxy is poured into the hole—dyed for visual clarity. Once the epoxy hardens, technicians drill through the hole. If a void is present, the epoxy will stick to the core and provide physical evidence.

Common stabilization materials include pozzolan-cement grout and polyurethane. The requirements for slab stabilization are strength and the ability to flow into or expand to fill small voids. Colloidal mixing equipment is necessary to use the pozzolan-cement grouts. The contractor must place the grout using a positive-displacement injection pump or a non-pulsing progressive cavity pump. A drill is also necessary but it must produce a clean hole with no surface spalling or breakouts. The injection devices must include a grout packer capable of sealing the hole. The injection device must also have a return hose or a fast-control reverse switch, in case workers detect slab movement on the uplift gauge. The uplift beam helps to monitor the slab deflection and has to have sensitive dial gauges.

Joint Sealing

Also called joint and crack repair, this method’s purpose is to minimize infiltration of surface water and incompressible material into the joint system. Joint sealants are also used to reduce dowel bar corrosion in Concrete Pavement Restoration (CPR)
International Grooving & Grinding Association
The International Grooving & Grinding Association is a non-profit trade association founded in 1972 that represents the industry that performs grooving and grinding of both concrete and asphalt surfaces in addition to Concrete Pavement Restoration and Concrete Pavement Preservation methods...

  techniques. Successful resealing consists of old sealant removal, shaping and cleaning the reservoir, installing the backer rod and installing the sealant. Sawing, manual removal, plowing and cutting are methods used to remove the old sealant. Saws are used to shape the reservoir. When cleaning the reservoir, no dust, dirt
Dirt
Dirt is unclean matter, especially when in contact with a person's clothes, skin or possessions when they are said to become dirty. Common types of dirt include:* dust — a general powder of organic or mineral matter...

 or traces of old sealant should remain. Thus, it is recommended to water wash, sand-blast and then air blow to remove any sand, dirt or dust. The backer rod installation requires a double-wheeled, steel roller to insert the rod to the desired depth. After inserting the backer rod, the sealant is placed into the joint. There are various materials to choose for this method including hot pour bituminous liquid, silicone and preformed compression seals.

Safety considerations


Careful design and construction of roads can increase Road traffic safety and reduce the harm (deaths, injuries, and property damage) on the highway
Highway
A highway is any public road. In American English, the term is common and almost always designates major roads. In British English, the term designates any road open to the public. Any interconnected set of highways can be variously referred to as a "highway system", a "highway network", or a...

 system from traffic collisions.

On neighborhood roads traffic calming
Traffic calming
Traffic calming is intended to slow or reduce motor-vehicle traffic in order to improve the living conditions for residents as well as to improve safety for pedestrians and cyclists. Urban planners and traffic engineers have many strategies for traffic calming...

, safety barriers
Safety barriers
A safety barrier is a component which prevents access to a dangerous area. In an industrial system, it is a guard such as a fence or window, designed to keep the operator away from moving parts or other hazards. It is commonly used to mitigate risk in the Hazard-Barrier-Target model, as studied in...

, pedestrian crossings and cycle lanes can all protect pedestrians and cyclists.

Lane
Lane
A lane is a part of the roadway within a road marked out for use by a single line of vehicles in such a way as to control and guide drivers for the purpose of reducing traffic conflicts. Most public roads have at least two lanes, one for traffic in each direction, separated by Lane markings...

 markers in some countries and states are marked with Cat's eyes
Cat's eye (road)
The cat's eye is a retroreflective safety device used in road marking and was the first of a range of raised pavement markers. It originated in the UK in 1933 and is today used all over the world....

 or Botts dots
Raised pavement marker
A raised pavement marker is a safety device used on roads. These devices are usually made with plastic, ceramic, or occasionally metal, and come in a variety of shapes and colors. Many varieties include a lens or sheeting that enhance their visibility by reflecting automotive headlights...

, bright reflectors that do not fade like paint. Botts dots are not used where it is icy in the winter, because frost and snowplows can break the glue that holds them to the road, although they can be embedded in short, shallow trenches carved in the roadway, as is done in the mountainous regions of California.

For major roads risk can be reduced by providing limited access from properties and local roads, grade separated junctions
Grade separation
Grade separation is the method of aligning a junction of two or more transport axes at different heights so that they will not disrupt the traffic flow on other transit routes when they cross each other. The composition of such transport axes does not have to be uniform; it can consist of a...

 and median dividers
Dual carriageway
A dual carriageway is a class of highway with two carriageways for traffic travelling in opposite directions separated by a central reservation...

 between opposite-direction traffic to reduce likelihood of head-on collisions.

The placement of energy attenuation devices (e.g. guardrails, wide grassy areas, sand barrels) is also common. Some road fixtures such as road signs and fire hydrants are designed to collapse on impact. Light poles are designed to break at the base rather than violently stop a car that hits them. Highway authorities may also remove larger trees from the immediate vicinity of the road.

Environmental performance

Careful design and construction of a road can reduce any negative environmental impacts.

Water management systems can be used to reduce the effect of pollutants from roads. Rainwater and snowmelt
Snowmelt
In hydrology, snowmelt is surface runoff produced from melting snow. It can also be used to describe the period or season during which such runoff is produced. Water produced by snowmelt is an important part of the annual water cycle in many parts of the world, in some cases contributing high...

 running off of roads tends to pick up gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...

, motor oil
Motor oil
Motor oil or engine oil is an oil used for lubrication of various internal combustion engines. The main function is to lubricate moving parts; it also cleans, inhibits corrosion, improves sealing, and cools the engine by carrying heat away from moving parts.Motor oils are derived from...

, heavy metals
Heavy metals
A heavy metal is a member of a loosely-defined subset of elements that exhibit metallic properties. It mainly includes the transition metals, some metalloids, lanthanides, and actinides. Many different definitions have been proposed—some based on density, some on atomic number or atomic weight,...

, trash
Waste
Waste is unwanted or useless materials. In biology, waste is any of the many unwanted substances or toxins that are expelled from living organisms, metabolic waste; such as urea, sweat or feces. Litter is waste which has been disposed of improperly...

 and other pollutants and result in Water pollution
Water pollution
Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....

. Road runoff is a major source of nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

, copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

, cadmium
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...

, lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

 and polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbons , also known as poly-aromatic hydrocarbons or polynuclear aromatic hydrocarbons, are potent atmospheric pollutants that consist of fused aromatic rings and do not contain heteroatoms or carry substituents. Naphthalene is the simplest example of a PAH...

s (PAHs), which are created as combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 byproducts of gasoline and other fossil fuel
Fossil fuel
Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...

s. De-icing chemicals and sand can run off into roadsides, contaminate groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...

 and pollute surface water
Surface water
Surface water is water collecting on the ground or in a stream, river, lake, wetland, or ocean; it is related to water collecting as groundwater or atmospheric water....

s; and road salts can be toxic to sensitive plants and animals. Sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

 applied to icy roads can be ground up by traffic into fine particulates and contribute to air pollution. Sand can alter stream bed
Stream bed
A stream bed is the channel bottom of a stream, river or creek; the physical confine of the normal water flow. The lateral confines or channel margins, during all but flood stage, are known as the stream banks or river banks. In fact, a flood occurs when a stream overflows its banks and flows onto...

 environments, causing stress for the plants and animals that live there.

Roads are a chief source of environmental noise generation. In the early 1970s it was recognized that design of roads can be conducted to influence and minimize noise generation. Noise barrier
Noise barrier
A noise barrier is an exterior structure designed to protect sensitive land uses from noise pollution...

s are used to reduce Noise pollution
Noise pollution
Noise pollution is excessive, displeasing human, animal or machine-created environmental noise that disrupts the activity or balance of human or animal life...

, in particular where roads are located close to built-up areas. Regulations can restrict the use of Engine braking
Engine braking
Engine braking is where the retarding forces within an engine are used to slow a vehicle down, as opposed to using an external braking mechanism, for example friction brakes or magnetic brakes....

.

Motor vehicle emissions
Motor vehicle emissions
Motor vehicle emissions are composed of the by-products that comes out of the exhaust systems or other emissions such as gasoline evaporation...

s contribute air pollution. Concentrations of air pollutants and adverse respiratory health effects are greater near the road than at some distance away from the road. Road dust kicked up by vehicles may trigger allergic reactions.

Terminology

  • Alignment (road) - horizontal and vertical curvature of a road.
  • Adverse camber - where a road slopes towards the outside of a bend, increasing the likelihood that vehicles travelling at speed will skid or topple. Usually only a temporary situation during road maintenance.
  • All-weather road - Unpaved road that is constructed of a material that does not create mud during rainfall.
  • Banked turn
    Banked turn
    A banked turn is a turn or change of direction in which the vehicle banks or inclines, usually towards the inside of the turn. The bank angle is the angle at which the vehicle is inclined about its longitudinal axis with respect to its path....

  • Camber - the curvature of the road surface that encourages surface water to flow freely from the carriageway, or on bends angling of the surface to lean traffic 'into the bend' reducing the chance of a skid.
  • Cant - superelevation
  • Cross slope
    Cross slope
    Cross slope is a geometric feature of pavement surfaces; the transversal slope [%] with respect to the horizon. It is a very important safety factor. One task is to make water run off the surface to a drainage system, as Cross Slope is the main contributor to Pavement Drainage gradient. Very low...

  • Grade - longitudinal slope

  • Belisha Beacon
    Belisha beacon
    A Belisha beacon is an amber-coloured globe lamp atop a tall black and white pole, marking pedestrian crossings of roads in the United Kingdom, Ireland and in other countries historically influenced by Britain...

     - an orange globe, lit at night, used to highlight a pedestrian crossing
    Pedestrian crossing
    A pedestrian crossing or crosswalk is a designated point on a road at which some means are employed to assist pedestrians wishing to cross. They are designed to keep pedestrians together where they can be seen by motorists, and where they can cross most safely across the flow of vehicular traffic...

    .
  • Bollard - Rigid posts that can be arranged in a line to close a road or path to vehicles above a certain width
  • Byway
    Byway (road)
    A byway in the United Kingdom is a minor secondary or tertiary road. In 2000 the legal term 'restricted byway' was introduced to cover roads on which it is possible to travel by any mode but not using 'mechanically propelled vehicles'.-Byway Open to All Traffic :In England & Wales, a Byway Open to...

     - Highway over which the public have a right to travel for vehicular and other kinds of traffic, but is used mainly as a footpath or bridleway
  • Bypass
    Bypass (road)
    A bypass is a road or highway that avoids or "bypasses" a built-up area, town, or village, to let through traffic flow without interference from local traffic, to reduce congestion in the built-up area, and to improve road safety....

     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
    Botts' dots
    Botts' dots are round nonreflective raised pavement markers. In many U.S. states and in several other countries, Botts' dots are used to mark lanes on highways and arterial roads. They provide tactile feedback to drivers when they move across designated travel lanes, and are analogous to rumble...

     - Non-reflective raised pavement marker
    Raised pavement marker
    A raised pavement marker is a safety device used on roads. These devices are usually made with plastic, ceramic, or occasionally metal, and come in a variety of shapes and colors. Many varieties include a lens or sheeting that enhance their visibility by reflecting automotive headlights...

     used on roads
  • Cat's eye
    Cat's eye (road)
    The cat's eye is a retroreflective safety device used in road marking and was the first of a range of raised pavement markers. It originated in the UK in 1933 and is today used all over the world....

     - reflective
    Reflection (physics)
    Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...

     raised pavement marker
    Raised pavement marker
    A raised pavement marker is a safety device used on roads. These devices are usually made with plastic, ceramic, or occasionally metal, and come in a variety of shapes and colors. Many varieties include a lens or sheeting that enhance their visibility by reflecting automotive headlights...

     used on roads
  • Central reservation
    Central reservation
    On divided roads, such as divided highways or freeways/motorways, the central reservation , median, parkway , median strip or central nature strip is the area which separates opposing lanes of traffic...

     - On dual carriageway
    Dual carriageway
    A dual carriageway is a class of highway with two carriageways for traffic travelling in opposite directions separated by a central reservation...

     roads, including controlled-access highway
    Controlled-access highway
    A controlled-access highway is a highway designed exclusively for high-speed vehicular traffic, with all traffic flow and ingress/egress regulated...

    s, divided highway
    Divided Highway
    Divided Highway is a compilation album by American rock band The Doobie Brothers, released in 2003. . All tracks are taken from the albums Cycles and Brotherhood .-Track listing:...

    s and many limited-access highways, the central reservation (British English
    British English
    British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...

    ), median (North American English
    North American English
    North American English is the variety of the English language of North America, including that of the United States and Canada. Because of their shared histories and the similarities between the pronunciation, vocabulary and accent of American English and Canadian English, the two spoken languages...

    ), median strip (North American English and Australian English
    Australian English
    Australian English is the name given to the group of dialects spoken in Australia that form a major variety of the English language....

    ), neutral ground [Louisiana English] or central nature strip (Australian English) - Area that separates opposing lane
    Lane
    A lane is a part of the roadway within a road marked out for use by a single line of vehicles in such a way as to control and guide drivers for the purpose of reducing traffic conflicts. Most public roads have at least two lanes, one for traffic in each direction, separated by Lane markings...

    s of traffic
    Traffic
    Traffic on roads may consist of pedestrians, ridden or herded animals, vehicles, streetcars and other conveyances, either singly or together, while using the public way for purposes of travel...

  • Chicane
    Chicane
    A chicane is an artificial feature creating extra turns in a road, used in motor racing and on city streets to slow cars to lower speeds.- Motor Racing :...

     - Sequence of tight serpentine curves (usually an S-shape curve or a bus stop)
  • Chipseal
    Chipseal
    Chip seal is a pavement surface treatment that combines a layer of asphalt with a layer of fine aggregate. In the United States, chip seals are typically used on rural roads carrying lower traffic volumes, and the process is often referred to as "asphaltic surface treatment"...

     - 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
    Asphalt concrete
    Asphalt concrete is a composite material commonly used in construction projects such as road surfaces, airports and parking lots. It consists of asphalt and mineral aggregate mixed together, then laid down in layers and compacted...

     or a concrete
    Concrete
    Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

    , in the U.S.
    United States
    The United States of America is a federal constitutional republic comprising fifty states and a federal district...

     it is usually only used on low volume rural roads
  • Corniche
    Corniche
    The word corniche typically refers to a road on the side of a cliff or mountain, with the ground rising on one side of the road and falling away on the other...

     - Road on the side of a cliff
    Cliff
    In geography and geology, a cliff is a significant vertical, or near vertical, rock exposure. Cliffs are formed as erosion landforms due to the processes of erosion and weathering that produce them. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually...

     or mountain
    Mountain
    Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...

    , with the ground rising on one side and falling away on the other
  • Curb
    Curb (road)
    A curb, or kerb , is the edge where a raised pavement/sidewalk/footpath, road median, or road shoulder meets an unraised street or other roadway.-Function:...

     (kerb) - A raised edge at the side of the roadway.
  • Curb extension
    Curb extension
    A curb extension is a traffic calming measure, primarily used to extend the sidewalk, reducing the crossing distance and allowing pedestrians about to cross and approaching vehicle drivers to see each other when vehicles...

     - (also kerb extension, bulb-out, nib, elephant ear, curb bulge and blister) Traffic calming
    Traffic calming
    Traffic calming is intended to slow or reduce motor-vehicle traffic in order to improve the living conditions for residents as well as to improve safety for pedestrians and cyclists. Urban planners and traffic engineers have many strategies for traffic calming...

     measure, intended to slow the speed of traffic and increase driver awareness, particularly in built-up and residential neighborhoods.
  • Drainage gradient
    Drainage gradient
    Drainage gradient is a term in road technology, defining the resulting vector of a road surface cross slope and longitudinal gradient .If the DG is too low, rain and melt water drainage will be insufficient...

  • Farm-to-market road - a state road or county road that connects rural or agricultural areas to market towns.
  • Fork - (literally "fork in the road") Type of intersection
    Intersection (road)
    An intersection is a road junction where two or more roads either meet or cross at grade . An intersection may be 3-way - a T junction or fork, 4-way - a crossroads, or 5-way or more...

     where a road splits
  • 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 millennium, similar to a Byway
    Byway (road)
    A byway in the United Kingdom is a minor secondary or tertiary road. In 2000 the legal term 'restricted byway' was introduced to cover roads on which it is possible to travel by any mode but not using 'mechanically propelled vehicles'.-Byway Open to All Traffic :In England & Wales, a Byway Open to...

  • Guard rail
    Guard rail
    Guard rail or guardrail, sometimes referred to as guide rail or railing, is a system designed to keep people or vehicles from straying into dangerous or off-limits areas...

     - Prevents vehicles from veering off the road into oncoming traffic, crashing against solid objects or falling from a road
  • Gutter
    Gutter
    panels of a comic strip or comic book page*Gutter , the space between panes of postage stamps that creates configurations of "gutter pairs" or "gutter blocks"*Gutter, in interface design, the blank spaces that separate rows and columns in screen...

     - UK a drainage channel between the main carriageway and the edge of the road.
  • Interstate Highway System
    Interstate Highway System
    The Dwight D. Eisenhower National System of Interstate and Defense Highways, , is a network of limited-access roads including freeways, highways, and expressways forming part of the National Highway System of the United States of America...

     - United States
    United States
    The United States of America is a federal constitutional republic comprising fifty states and a federal district...

     System of Interstate and Defense Highways
  • Layby (Pullout, pull-off) - A paved area beside a main road where cars can stop temporarily to let another car pass.
  • Loose chippings
    Loose chippings
    Loose chippings are stone fragments which have become detached from a road surface and form a hazard to vehicles using that road.They may be the result of a poorly constructed chip seal, when unbound surplus aggregate is not removed from the surface. Another cause is of a chip seal or asphalt...

     - the hazard of stone chippings that have come loose
  • Median
    Central reservation
    On divided roads, such as divided highways or freeways/motorways, the central reservation , median, parkway , median strip or central nature strip is the area which separates opposing lanes of traffic...

     - On dual carriageway
    Dual carriageway
    A dual carriageway is a class of highway with two carriageways for traffic travelling in opposite directions separated by a central reservation...

     roads, including controlled-access highway
    Controlled-access highway
    A controlled-access highway is a highway designed exclusively for high-speed vehicular traffic, with all traffic flow and ingress/egress regulated...

    s, divided highway
    Divided Highway
    Divided Highway is a compilation album by American rock band The Doobie Brothers, released in 2003. . All tracks are taken from the albums Cycles and Brotherhood .-Track listing:...

    s and many limited-access highways, the central reservation (British English
    British English
    British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...

    ), median (North American English
    North American English
    North American English is the variety of the English language of North America, including that of the United States and Canada. Because of their shared histories and the similarities between the pronunciation, vocabulary and accent of American English and Canadian English, the two spoken languages...

    ), median strip (North American English and Australian English
    Australian English
    Australian English is the name given to the group of dialects spoken in Australia that form a major variety of the English language....

    ), neutral ground [Louisiana English] or central nature strip (Australian English) - Area that separates opposing lane
    Lane
    A lane is a part of the roadway within a road marked out for use by a single line of vehicles in such a way as to control and guide drivers for the purpose of reducing traffic conflicts. Most public roads have at least two lanes, one for traffic in each direction, separated by Lane markings...

    s of traffic
    Traffic
    Traffic on roads may consist of pedestrians, ridden or herded animals, vehicles, streetcars and other conveyances, either singly or together, while using the public way for purposes of travel...

  • Mountain pass
    Mountain pass
    A mountain pass is a route through a mountain range or over a ridge. If following the lowest possible route, a pass is locally the highest point on that route...

     - Lower point that allows easier access through a range of mountains
  • Milestone
    Milestone
    A milestone is one of a series of numbered markers placed along a road or boundary at intervals of one mile or occasionally, parts of a mile. They are typically located at the side of the road or in a median. They are alternatively known as mile markers, mileposts or mile posts...

     - One of a series of numbered markers placed along a road at regular intervals, showing the distance to destinations.
  • National Highway
    National Highway
    The term national highway may refer to:* National Highway * National Highway System * National Trunk Highway System or China National Highways* National Highways of India* National highways of Japan...

     - Road built and maintained by a national authority.
  • Pavement
    Pavement (material)
    Road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past cobblestones and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete. Such...

     - The road regarded as a geoconstruction. In the UK the term is road surface and the pavement is a pedestrian walkway alongside the road.
  • Pedestrian crossing
    Pedestrian crossing
    A pedestrian crossing or crosswalk is a designated point on a road at which some means are employed to assist pedestrians wishing to cross. They are designed to keep pedestrians together where they can be seen by motorists, and where they can cross most safely across the flow of vehicular traffic...

     - Designated point on a road where road marking or other means helps pedestrians cross safely
  • Pelican crossing
    Pelican crossing
    A Pelican crossing is a type of pedestrian crossing featuring a pair of poles each with a standard set of traffic lights facing oncoming traffic, a push button and two illuminated, coloured men facing the pedestrian from across the road - a red, stationary man to indicate that it is not safe to...

     - (officially Pelicon crossing) UK a PEdestrian LIght CONtrolled crossing.
  • Private highway
    Private highway
    A private highway is a highway owned and operated for profit by private industry. Private highways are common in Asia and Europe; in addition, a few have been built in the United States on an experimental basis...

     - Highway owned and operated for profit by private industry
  • Private road
    Private road
    A private road is a road owned and maintained by a private individual, organization, or company rather than by a government.Consequently, unauthorized use of the road may be considered trespassing, and some of the usual rules of the road may not apply...

     - Road owned and maintained by a private individual
    Person
    A person is a human being, or an entity that has certain capacities or attributes strongly associated with being human , for example in a particular moral or legal context...

    , organization
    Organization
    An organization is a social group which distributes tasks for a collective goal. The word itself is derived from the Greek word organon, itself derived from the better-known word ergon - as we know `organ` - and it means a compartment for a particular job.There are a variety of legal types of...

    , or company
    Company
    A company is a form of business organization. It is an association or collection of individual real persons and/or other companies, who each provide some form of capital. This group has a common purpose or focus and an aim of gaining profits. This collection, group or association of persons can be...

     rather than by a government
    Government
    Government refers to the legislators, administrators, and arbitrators in the administrative bureaucracy who control a state at a given time, and to the system of government by which they are organized...

  • Public space
    Public space
    A public space is a social space such as a town square that is open and accessible to all, regardless of gender, race, ethnicity, age or socio-economic level. One of the earliest examples of public spaces are commons. For example, no fees or paid tickets are required for entry, nor are the entrants...

     - Place where anyone has a right to come without being excluded because of economic or social
    Socioeconomics
    Socioeconomics or socio-economics or social economics is an umbrella term with different usages. 'Social economics' may refer broadly to the "use of economics in the study of society." More narrowly, contemporary practice considers behavioral interactions of individuals and groups through social...

     conditions
  • Ranch road - U.S.
    United States
    The United States of America is a federal constitutional republic comprising fifty states and a federal district...

     road that connects rural
    Rural
    Rural areas or the country or countryside are areas that are not urbanized, though when large areas are described, country towns and smaller cities will be included. They have a low population density, and typically much of the land is devoted to agriculture...

     and agricultural areas to market town
    Market town
    Market town or market right is a legal term, originating in the medieval period, for a European settlement that has the right to host markets, distinguishing it from a village and city...

    s
  • Road number
    Road number
    A road number is 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, two-lane roads, and so forth.-United Kingdom:...

     - Often assigned to identify a stretch of public roads—often dependent on the type of road
    Types of road
    Many types of road exist around the world, all of which are thoroughfares which can be used by motorized traffic. Roads are not necessarily available for use by the general public without permission, highways are available for by the public, although a toll may be charged...

    , with numbers differentiating between interstate
    Interstate Highway System
    The Dwight D. Eisenhower National System of Interstate and Defense Highways, , is a network of limited-access roads including freeways, highways, and expressways forming part of the National Highway System of the United States of America...

    s, motorways, arterial thoroughfares
    Arterial road
    An arterial road, or arterial thoroughfare, is a high-capacity urban road. The primary function of an arterial road is to deliver traffic from collector roads to freeways, and between urban centres at the highest level of service possible. As such, many arteries are limited-access roads, or feature...

    , etc.
  • Road-traffic safety
    Road-traffic safety
    The term road traffic safety is about the risk of a person being killed or seriously injured while using the road network as a pedestrian, cyclist, motorist or user of on road public transport...

     - Process to reduce the harm (deaths, injuries, and property damage) that result from vehicle crashes on public roads
  • Roadworks
    Roadworks
    Roadworks occur when part of the road, or in rare cases, the entire road, has to be occupied for work relating to the road, most often in the case of road surface repairs...

     - Part or all of the road is occupied for work or maintenance
  • 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.
  • Roundabout
    Roundabout
    A roundabout is the name for a road junction in which traffic moves in one direction around a central island. The word dates from the early 20th century. Roundabouts are common in many countries around the world...

     UK a road junction where typically three or more roads are joined by a circular section of road. Traffic 'on the roundabout' has priority over traffic on approach roads, unless indicated otherwise. In countrys where traffic drives on the left the roundabout is travelled in a clockwise direction. Also known as an island
    Roundabout
    A roundabout is the name for a road junction in which traffic moves in one direction around a central island. The word dates from the early 20th century. Roundabouts are common in many countries around the world...

     in parts of the UK.
  • Shoulder
    Shoulder (road)
    A hard shoulder, or simply shoulder, is a reserved area by the verge of a road or motorway. Generally it is kept clear of motor vehicle traffic...

     (also hand-shoulder) - A clear, level paved area to the side of the roadway available for stopping if required.
  • State highway
    State highway
    State highway, state road or state route can refer to one of three related concepts, two of them related to a state or provincial government in a country that is divided into states or provinces :#A...

     - Road numbered by the state, falling below numbered national highways (like U.S. Routes
    United States Numbered Highways
    The system of United States Numbered Highways is an integrated system of roads and highways in the United States numbered within a nationwide grid...

    ) in the hierarchy or a road maintained by the state, including nationally-numbered highways
  • Texture (roads)
    Texture (roads)
    Road surface texture are deviations from a planar surface, affecting the vehicle/tyre interaction. Pavement texture is divided into:* Microtexture with wavelengths from 0 mm up to 0.5 mm* Macrotexture with wavelengths from 0.5 mm up to 50 mm...

     - 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
    Traffic calming
    Traffic calming is intended to slow or reduce motor-vehicle traffic in order to improve the living conditions for residents as well as to improve safety for pedestrians and cyclists. Urban planners and traffic engineers have many strategies for traffic calming...

     - Set of strategies used by urban planner
    Urban planner
    An urban planner or city planner is a professional who works in the field of urban planning/land use planning for the purpose of optimizing the effectiveness of a community's land use and infrastructure. They formulate plans for the development and management of urban and suburban areas, typically...

    s and traffic engineers
    Traffic engineering (transportation)
    For the engineering of communications and computer networks, see Teletraffic engineering.Traffic engineering is a branch of civil engineering that uses engineering techniques to achieve the safe and efficient movement of people and goods on roadways...

     to slow down or reduce traffic
    Traffic
    Traffic on roads may consist of pedestrians, ridden or herded animals, vehicles, streetcars and other conveyances, either singly or together, while using the public way for purposes of travel...

    , thereby improving safety for pedestrian
    Pedestrian
    A pedestrian is a person traveling on foot, whether walking or running. In some communities, those traveling using roller skates or skateboards are also considered to be pedestrians. In modern times, the term mostly refers to someone walking on a road or footpath, but this was not the case...

    s and bicyclists
    Bicycle-friendly
    The term bicycle-friendly describes policies and practices which may help some people feel more comfortable about traveling by bicycle with other traffic...

     and improving the environment for residents
  • Traffic island
    Traffic island
    A traffic island is a solid or painted object in a road that channelises traffic. It can also be a narrow strip of island between roads that intersect at an acute angle. If the island uses road markings only, without raised kerbs or other physical obstructions, it is called a painted island...

     - UK a small raised area used to help define the traffic flow, which may also act as a refuge for pedestrians crossing the carriageway or a location for signs, barriers or lights—a synonym for roundabout
    Roundabout
    A roundabout is the name for a road junction in which traffic moves in one direction around a central island. The word dates from the early 20th century. Roundabouts are common in many countries around the world...

     in some parts of the UK
  • Traffic light
    Traffic light
    Traffic lights, which may also be known as stoplights, traffic lamps, traffic signals, signal lights, robots or semaphore, are signalling devices positioned at road intersections, pedestrian crossings and other locations to control competing flows of traffic...

     - Also known as a traffic signal, stop light, stop-and-go lights—a signaling device at a road intersection, pedestrian crossing
    Pedestrian crossing
    A pedestrian crossing or crosswalk is a designated point on a road at which some means are employed to assist pedestrians wishing to cross. They are designed to keep pedestrians together where they can be seen by motorists, and where they can cross most safely across the flow of vehicular traffic...

    , or other location that assigns right of way to different approaches to an intersection
  • Zebra Crossing
    Zebra crossing
    A zebra crossing is a type of pedestrian crossing used in many places around the world. Its distinguishing feature is alternating dark and light stripes on the road surface, from which it derives its name. A zebra crossing typically gives extra rights of way to pedestrians.The use of zebra...

     - UK a pedestrian crossing
    Pedestrian crossing
    A pedestrian crossing or crosswalk is a designated point on a road at which some means are employed to assist pedestrians wishing to cross. They are designed to keep pedestrians together where they can be seen by motorists, and where they can cross most safely across the flow of vehicular traffic...

     marked by black and white stripes on the carriageway

Right- and left-hand traffic

Traffic
Traffic
Traffic on roads may consist of pedestrians, ridden or herded animals, vehicles, streetcars and other conveyances, either singly or together, while using the public way for purposes of travel...

 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 sign
Traffic sign
Traffic signs or road signs are signs erected at the side of roads to provide information to road users. With traffic volumes increasing over the last eight decades, many countries have adopted pictorial signs or otherwise simplified and standardized their signs to facilitate international travel...

s are mostly on the right side of the road, roundabout
Roundabout
A roundabout is the name for a road junction in which traffic moves in one direction around a central island. The word dates from the early 20th century. Roundabouts are common in many countries around the world...

s and traffic circle
Traffic circle
A traffic circle or rotary is a type of circular intersection in which traffic must travel in one direction around a central island. In some countries, traffic entering the circle has the right-of-way and drivers in the circle must yield. In many other countries, traffic entering the circle must...

s go counter-clockwise/anti-clockwise, and pedestrian
Pedestrian
A pedestrian is a person traveling on foot, whether walking or running. In some communities, those traveling using roller skates or skateboards are also considered to be pedestrians. In modern times, the term mostly refers to someone walking on a road or footpath, but this was not the case...

s 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 33% of the world by population
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...

 drive on the left, and 67% keep right. By road distances, about 28% drive on the left, and 72% on the right, even though originally most traffic drove on the left worldwide.

Economics

Transport economics
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...

 is used to understand both the relationship between the transport system and the wider economy and the complex network effect
Network effect
In economics and business, a network effect is the effect that one user of a good or service has on the value of that product to other people. When network effect is present, the value of a product or service is dependent on the number of others using it.The classic example is the telephone...

s when there are multiple paths and competing modes for both personal and freight (road/rail/air/ferry) and where Induced demand
Induced demand
Induced demand, or latent demand, is the phenomenon that after supply increases, more of a good is consumed. This is entirely consistent with the economic theory of supply and demand; however, this idea has become important in the debate over the expansion of transportation systems, and is often...

 can result in increased on decreased transport levels when road provision is increased by building new roads or decreased (for example California State Route 480). Roads are generally built and maintained by the public sector
Public sector
The public sector, sometimes referred to as the state sector, is a part of the state that deals with either the production, delivery and allocation of goods and services by and for the government or its citizens, whether national, regional or local/municipal.Examples of public sector activity range...

 using taxation although implementation may be through private
Private sector
In economics, the private sector is that part of the economy, sometimes referred to as the citizen sector, which is run by private individuals or groups, usually as a means of enterprise for profit, and is not controlled by the state...

 contractors
General contractor
A general contractor is responsible for the day-to-day oversight of a construction site, management of vendors and trades, and communication of information to involved parties throughout the course of a building project.-Description:...

). or occasionally using road tolls
Toll road
A toll road is a privately or publicly built road for which a driver pays a toll for use. Structures for which tolls are charged include toll bridges and toll tunnels. Non-toll roads are financed using other sources of revenue, most typically fuel tax or general tax funds...

.

Economics
Economics
Economics is the social science that analyzes the production, distribution, and consumption of goods and services. The term economics comes from the Ancient Greek from + , hence "rules of the house"...

 and society
Society
A society, or a human society, is a group of people related to each other through persistent relations, or a large social grouping sharing the same geographical or virtual territory, subject to the same political authority and dominant cultural expectations...

 depend heavily on efficient roads. In the European Union (EU)
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

 44% of all goods
Good (economics and accounting)
In economics, a good is something that is intended to satisfy some wants or needs of a consumer and thus has economic utility. It is normally used in the plural form—goods—to denote tangible commodities such as products and materials....

 are moved by truck
Truck
A truck or lorry is a motor vehicle designed to transport cargo. Trucks vary greatly in size, power, and configuration, with the smallest being mechanically similar to an automobile...

s over roads and 85% of all person
Person
A person is a human being, or an entity that has certain capacities or attributes strongly associated with being human , for example in a particular moral or legal context...

s are transported by car
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

s, bus
Bus
A bus is a road vehicle designed to carry passengers. Buses can have a capacity as high as 300 passengers. The most common type of bus is the single-decker bus, with larger loads carried by double-decker buses and articulated buses, and smaller loads carried by midibuses and minibuses; coaches are...

es or coaches on roads. The term was also commonly used to refer to roadstead
Roadstead
A roadstead is a place outside a harbor where a ship can lie at anchor. It is an enclosed area with an opening to the sea, narrower than a bay or gulf. It has a surface that cannot be confused with an estuary. It can be created artificially by jetties or dikes...

s, waterways that lent themselves to use by shipping.

Construction costs

According to the New York State Thruway Authority, some sample per-mile costs to construct multi-lane roads in several US northeastern states were:
  • Connecticut Turnpike — $3,449,000 per mile
  • New Jersey Turnpike — $2,200,000 per mile
  • Pennsylvania Turnpike (Delaware Extension) — $1,970,000 per mile
  • Northern Indiana Toll Road — $1,790,000 per mile
  • Garden State Parkway — $1,720,000 per mile
  • Massachusetts Turnpike — $1,600,000 per mile
  • Thruway, New York to Pennsylvania Line — $1,547,000 per mile
  • Ohio Turnpike — $1,352,000 per mile
  • Pennsylvania Turnpike (early construction) — $736,000 per mile

Statistics

The United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 has the largest network of roads of any country with 6430366 kilometres (3,995,654.1 mi) (2005). The People's Republic of China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...

 is second with 3583715 kilometres (2,226,822.8 mi) of road (2007) See List of countries by road network size. The Republic of India has the third largest road system in the world with 3383344 kilometres (2,102,317.7 mi) (2002). When looking only at expressways the National Trunk Highway System (NTHS) in People's Republic of China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...

has a total length of 45000 kilometres (27,961.8 mi) at the end of 2006, and 60,300 km at the end of 2008, second only to the United States with 90000 kilometres (55,923.5 mi) in 2005.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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