Roads From Henfield And From Poyning's Common (Sussex) Act 1798
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A road is a linear way for the conveyance of traffic that mostly has an improved surface for use by vehicles (motorized and non-motorized) and pedestrians. Unlike
street A street is a 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, ...
s, the main function of roads is transportation. There are many types of roads, including
parkway A parkway is a landscaped thoroughfare.''"parkway."''Webster's Third New International Dictionary, Unabridged. Merriam-Webster, 2002. http://unabridged.merriam-webster.com (14 Apr. 2007). The term is particularly used for a roadway in a park or ...
s, avenues,
controlled-access highway A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway and expressway. Other similar terms i ...
s (freeways, motorways, and expressways), tollways, interstates, highways, thoroughfares, and local roads. The primary features of roads include lanes,
sidewalk A sidewalk (North American English), pavement (British English), footpath in Australia, India, New Zealand and Ireland, or footway, is a path along the side of a street, street, highway, terminals. Usually constructed of concrete, pavers, brick ...
s (pavement), roadways (carriageways),
medians The Medes ( Old Persian: ; Akkadian: , ; Ancient Greek: ; Latin: ) were an ancient Iranian people who spoke the Median language and who inhabited an area known as Media between western and northern Iran. Around the 11th century BC, th ...
, shoulders, verges, bike paths (cycle paths), and shared-use paths.


Definitions

Historically many roads were simply recognizable routes without any formal construction or some maintenance. The
Organization for Economic Co-operation and Development The Organisation for Economic Co-operation and Development (OECD; french: Organisation de coopération et de développement économiques, ''OCDE'') is an intergovernmental organisation with 38 member countries, founded in 1961 to stimulate e ...
(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". The
Eurostat Eurostat ('European Statistical Office'; DG ESTAT) is a Directorate-General of the European Commission located in the Kirchberg, Luxembourg, Kirchberg quarter of Luxembourg City, Luxembourg. Eurostat's main responsibilities are to provide statis ...
, ITF and UNECE ''Glossary for Transport Statistics Illustrated'' defines a road as a "Line of communication (traveled way) open to public traffic, primarily for the use of road motor vehicles, using a stabilized base other than rails or air strips. ..Included are paved roads and other roads with a stabilized base, e.g. gravel roads. Roads also cover streets, bridges, tunnels, supporting structures, junctions, crossings and interchanges. Toll roads are also included. Excluded are dedicated cycle lanes." The 1968 Vienna Convention on Road Traffic defines a road as the entire surface of any way or street open to public traffic. In urban areas roads may diverge through a city or village and be named as streets, serving a dual function as urban space easement and route. Modern roads are normally smoothed, paved, or otherwise prepared to allow easy travel.


Australia

Part 2, Division 1, clauses 11-13 of the National Transport Commission Regulations 2006 defines a road in Australia as 'an area that is open to or used by the public and is developed for, or has as one of its main uses, the driving or riding of motor vehicles.' Further, it defines a shoulder (typical an area of the road outside the edge line, or the curb) and a road-related area which includes green areas separating roads, areas designated for cyclists and areas generally accessible to the public for driving, riding or parking vehicles.


New Zealand

In New Zealand, the definition of a road is broad in common law where the statutory definition includes areas the public has access to, by right or not. Beaches, publicly accessible car parks and yards (even if privately owned), river beds, road shoulders (verges), wharves and bridges are included. However, the definition of a road for insurance purposes may be restricted to reduce risk.


United Kingdom

In the United Kingdom ''
The Highway Code ''The Highway Code'' is a set of information, advice, guides and mandatory rules for road users in the United Kingdom. Its objective is to promote road safety. The ''Highway Code'' applies to all road users including pedestrians, horse riders ...
'' details rules for "road users", but there is some ambiguity between the terms ''highway'' and ''road''. For the purposes of the
English law English law is the common law legal system of England and Wales, comprising mainly criminal law and civil law, each branch having its own courts and procedures. Principal elements of English law Although the common law has, historically, be ...
, Highways Act 1980, which covers England and Wales but not Scotland or Northern Ireland, road is "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 footpaths, bridleways and cycle tracks, and also road and driveways on private land and many car parks. Vehicle Excise Duty, a road use tax, is payable on some vehicles used on the public road. The definition of a road depends on the definition of a highway; 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 A footpath (also pedestrian way, walking trail, nature trail) is a type of thoroughfare that is intended for use only by pedestrians and not other forms of traffic such as motorized vehicles, bicycles and horses. They can be found in a wide ...
s,
bridleway A bridle path, also bridleway, equestrian trail, horse riding path, ride, bridle road, or horse trail, is a trail or a thoroughfare that is used by people riding horses, riding on horses. Trails originally created for use by horses often now s ...
s, driftways, etc., it can now be used to mean those ways that allow the movement of motor vehicles, and the term ''
rights of way Right of way is the legal right, established by grant from a landowner or long usage (i.e. by Easement#Easement by prescription, prescription), to pass along a specific route through property belonging to another. A similar ''right of access'' ...
'' can be used to cover the wider usage.


United States

In the United States, laws distinguish between ''public roads'', which are open to public use, and ''private roads'', which are privately controlled.


History

The assertion that the first pathways were the trails made by animals has not been universally accepted; in many cases animals do not follow constant paths. Some believe that some roads originated from following animal trails. The Icknield Way may exemplify this type of road origination, where human and animal both selected the same natural line. By about 10,000 BC human travelers used rough roads/pathways. * The world's oldest known paved road was constructed in Egypt some time between 2600 and 2200 BC. * Stone-paved streets appear in the city of Ur in the Middle East dating back to 4000 BC. *
Corduroy road A corduroy road or log road is a type of road or timber trackway made by placing logs, perpendicular to the direction of the road over a low or swampy area. The result is an improvement over impassable mud or dirt roads, yet rough in the bes ...
s (log roads) are found dating to 4000 BC in Glastonbury, England. * The Sweet Track, a timber track causeway in England, is one of the oldest engineered roads discovered and the oldest timber trackway discovered in Northern Europe. Built in winter 3807 BC or spring 3806 BC, (tree-ring dating –
dendrochronology Dendrochronology (or tree-ring dating) is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed. As well as dating them, this can give data for dendroclimatology, the study of climate and atmos ...
– enabled very precise dating). It was claimed to be the oldest road in the world until the 2009 discovery of a 6,000-year-old trackway in
Plumstead Plumstead is an area in southeast London, within the Royal Borough of Greenwich, England. It is located east of Woolwich. History Until 1965, Plumstead was in the historic counties of England, historic county of Kent and the detail of mu ...
, London. * Brick-paved streets appeared in India as early as 3000 BC. * 1995 BC: an early subdividing of roadways evidenced with
sidewalk A sidewalk (North American English), pavement (British English), footpath in Australia, India, New Zealand and Ireland, or footway, is a path along the side of a street, street, highway, terminals. Usually constructed of concrete, pavers, brick ...
s built in Anatolia. * In 500 BC, Darius I the Great started an extensive road system for the
Achaemenid Empire The Achaemenid Empire or Achaemenian Empire (; peo, 𐎧𐏁𐏂, , ), also called the First Persian Empire, was an ancient Iranian empire founded by Cyrus the Great in 550 BC. Based in Western Asia, it was contemporarily the largest em ...
(Persia), including the Royal Road, which was one of the finest highways of its time, connecting Sardis (the westernmost major city of the empire) to
Susa Susa ( ; Middle elx, 𒀸𒋗𒊺𒂗, translit=Šušen; Middle and Neo- elx, 𒋢𒋢𒌦, translit=Šušun; Neo-Elamite and Achaemenid elx, 𒀸𒋗𒐼𒀭, translit=Šušán; Achaemenid elx, 𒀸𒋗𒐼, translit=Šušá; fa, شوش ...
. The road remained in use after Roman times. These road systems reached as far east as
Bactria Bactria (; Bactrian: , ), or Bactriana, was an ancient region in Central Asia in Amu Darya's middle stream, stretching north of the Hindu Kush, west of the Pamirs and south of the Gissar range, covering the northern part of Afghanistan, southwe ...
and India. * In ancient times, transport by river was far easier and faster than transport by road, especially considering the cost of road construction and the difference in carrying capacity between
cart A cart or dray (Australia and New Zealand) 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. It is different from the flatbed tr ...
s and river barges. A hybrid of road transport and ship transport beginning in about 1740 is the horse-drawn boat in which the horse follows a cleared path along the river bank. * From about 312 BC, the Roman Empire built straight strong stone
Roman road Roman roads ( la, viae Romanae ; singular: ; meaning "Roman way") were physical infrastructure vital to the maintenance and development of the Roman state, and were built from about 300 BC through the expansion and consolidation of the Roman Re ...
s throughout Europe and North Africa, in support of its military campaigns. At its peak the Roman Empire was connected by 29 major roads moving out from Rome and covering 78,000 kilometers or 52,964 Roman miles of paved roads. * In the 8th century AD, many roads were built throughout the
Arab Empire A caliphate or khilāfah ( ar, خِلَافَة, ) is an institution or public office under the leadership of an Islamic steward with the title of caliph (; ar, خَلِيفَة , ), a person considered a political-religious successor to th ...
. The most sophisticated roads were those in Baghdad, which were paved with tar. Tar was derived from petroleum, accessed from
oil field A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations. Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presence ...
s in the region, through the chemical process of destructive distillation. * The Highways Act 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) of engineered roads. The Rebecca Riots in Carmarthenshire and Rhayader from 1839 to 1844 contributed to a Royal Commission that led to the demise of the system in 1844, which coincided with the development of the UK railway system. * In the late-19th century roading engineers began to cater for cyclists by building separate lanes alongside roadways. * From the beginning of the 20th century, roads were increasingly built for tourism and also to create jobs. A typical example of the stimulation of tourism is the Great Dolomite Road, while the creation of the panoramic coastal road
Strada Costiera Strada is a chain based in the United Kingdom of branded restaurants specialising in Italian cuisine with two Strada sites and six Coppa Clubs, all in Southern England. History The concept was spawned by Luke Johnson in 2000 and, over five ...
between Duino and Barcola in 1928 was very much focused on creating jobs.


Design

Road design is part of highway engineering. Structural road design is designing a road for the 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 roadsides.


Terminology

; 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. ;
Alignment Alignment may refer to: Archaeology * Alignment (archaeology), a co-linear arrangement of features or structures with external landmarks * Stone alignment, a linear arrangement of upright, parallel megalithic standing stones Biology * Structu ...
: The route of the road, defined as a series of horizontal tangents and curves. ;All-weather road: Unpaved road that is constructed of a material that does not create mud during rainfall. ; Banked turn ; Belisha Beacon: An orange globe, lit at night, used to highlight a pedestrian crossing ; Bicycle boulevard: A street that allows local vehicle traffic, but is prioritized for bicycles and other non-motorized travel ; ;
Bollard A bollard is a sturdy, short, vertical post. The term originally referred to a post on a ship or quay used principally for mooring boats. It now also refers to posts installed to control road traffic and posts designed to prevent automotive v ...
: Rigid posts that can be arranged in a line to close a road or path to vehicles above a certain width ; Byway: Highway over which the public have a right to travel for vehicular and other kinds of traffic, but is used mainly as a footpath or bridleway ;
Bypass Bypass may refer to: * Bypass (road), a road that avoids a built-up area (not to be confused with passing lane) * Flood bypass of a river Science and technology Medicine * Bypass surgery, a class of surgeries including for example: ** Heart bypas ...
: 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 (turtles in Washington and Oregon or buttons in Texas and other southern states) are round non-reflective raised pavement markers. In many parts of the US, Botts' dots are used, along with reflective raised pavement markers, to ma ...
: Non-reflective raised pavement marker used on roads ; Camber (or crown): The slope of the
road surface A road surface (British English), or pavement (American English), 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, gravel road surfaces, hoggin, cobbles ...
downwards away from the centre of the road, so that surface water can flow freely to the edge of the carriageway, or on bends angling of the surface to lean traffic 'into the bend' reducing the chance of a skid. ; Cant: Another name for cross slope or camber ; Carriageway: Part of the road intended for the movement of road motor vehicles; the parts of the road which form a shoulder for the lower or upper layers of the road surface are not part of the roadway, nor are those parts of the road intended for the circulation of road vehicles which are not self-propelled or for the parking of vehicles. ; Cat's eye: Reflective raised pavement marker used on roads ; Chicane: Sequence of tight serpentine curves (usually an S-shape curve or a bus stop) ; Chipseal: Road surface composed of a thin layer of crushed stone 'chips' and asphalt emulsion. It seals the surface and protects it from weather, but provides no structural strength. It is cheaper than
asphalt concrete Asphalt concrete (commonly called asphalt, blacktop, or pavement in North America, and tarmac, bitumen macadam, or rolled asphalt in the United Kingdom and the Republic of Ireland) is a composite material commonly used to surface roads, parkin ...
or concrete. In the United States, it is usually only used on low volume rural roads ; Corniche: Road on the side of a cliff or mountain, with the ground rising on one side and falling away on the other ; Cross slope: The slope of the pavement, expressed as units of rise per unit of run, or as a percentage ; Curb (kerb): A raised edge at the side of the roadway. ;
Curb extension A curb extension (or also neckdown, kerb extension, bulb-out, bump-out, kerb build-out, nib, elephant ear, curb bulge, curb bulb, or blister) is a traffic calming measure which widens the sidewalk for a short distance. This reduces the crossing ...
: (also kerb extension, bulb-out, nib, elephant ear, curb bulge and blister) Traffic calming measure, intended to slow the speed of traffic and increase driver awareness, particularly in built-up and residential neighborhoods. ; Cycle lane: Part of a carriageway designated for cycles and distinguished from the rest of the carriageway by longitudinal road markings. Mopeds may also be allowed to use a cycle lane. ; Cycle track: Independent road or part of a road designated for cycles and sign-posted as such. A cycle track is separated from other roads or other parts of the same road by structural means. Mopeds may also be allowed to use the cycle track. ;
Cycling infrastructure Cycling infrastructure is all infrastructure cyclists are allowed to use. Bikeways include bike paths, bike lanes, cycle tracks, rail trails and, where permitted, sidewalks. Roads used by motorists are also cycling infrastructure, except whe ...
: Cycling-friendly infrastructure integrated into the roadway or in its own right of way ; Drainage gradient ; 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 In mathematics, the intersection of two or more objects is another object consisting of everything that is contained in all of the objects simultaneously. For example, in Euclidean geometry, when two lines in a plane are not parallel, their i ...
where a road splits ; Grade: Longitudinal slope ; Green lane: (UK) Unsurfaced road, may be so infrequently used that vegetation colonises freely, hence 'green'. Many green lanes are ancient routes that have existed for millennia. ; Guide rail: Prevents vehicles from veering off the road into oncoming traffic, crashing against solid objects or falling from a road. Also called a
guard rail Guard rail, guardrails, or protective guarding, in general, are a boundary feature and may be a means to prevent or deter access to dangerous or off-limits areas while allowing light and visibility in a greater way than a fence. Common shapes ...
or traffic barrier. ; Gutter: A drainage channel usually at the edge of the road or along a median. ; Interstate Highway System (United States): System of Interstate and Defense Highways ; Lane: One of the longitudinal strips into which a carriageway is divisible, whether or not defined by longitudinal road markings, which is wide enough for one moving line of motor vehicles other than motorcycles. ;
Layby A rest area is a public facility located next to a large thoroughfare such as a motorway, expressway, or highway, at which drivers and passengers can rest, eat, or refuel without exiting onto secondary roads. Other names include motorway serv ...
(Pullout, pull-off): A paved area beside a
main road A "main road" may refer to: * A major road in a town or village, or in a country area. * A highway * A trunk road, especially in British English Main Road may refer to: * Main Road, Hobart, Australia * Main Road, Cox's Bazar, Bangladesh * Main R ...
where
car A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarded as ...
s can stop temporarily to let another car pass. ; Loose chippings: The hazard of stone chippings that have come loose ;
Median In statistics and probability theory, the median is the value separating the higher half from the lower half of a data sample, a population, or a probability distribution. For a data set, it may be thought of as "the middle" value. The basic fe ...
: On
dual carriageway A dual carriageway ( BE) or divided highway ( AE) is a class of highway with carriageways for traffic travelling in opposite directions separated by a central reservation (BrE) or median (AmE). Roads with two or more carriageways which are ...
roads, including
controlled-access highway A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway and expressway. Other similar terms i ...
s, divided highways and many
limited-access road A limited-access road, known by various terms worldwide, including limited-access highway, dual-carriageway, expressway, limited access freeway, and partial controlled access highway, is a highway or arterial road for high-speed traffic which ...
s, the central reservation ( British English), median ( North American English), median strip (North American English and
Australian English Australian English (AusE, AusEng, AuE, AuEng, en-AU) is the set of varieties of the English language native to Australia. It is the country's common language and ''de facto'' national language; while Australia has no official language, Engli ...
), neutral ground ouisiana Englishor central nature strip (Australian English): Area that separates opposing lanes of traffic ; Motorway: (Europe) (Freeways in the US, Special road in the UK) Road, specially designed and built for motor traffic, which does not serve properties bordering on it, with separate carriageways for traffic in two directions, with no crossings at the same level (road, railway, tramway track, or footpath) and sign-posted as a motorway and is reserved for specific categories of road motor vehicles. ;
Mountain pass A mountain pass is a navigable route through a mountain range or over a ridge. Since many of the world's mountain ranges have presented formidable barriers to travel, passes have played a key role in trade, war, and both Human migration, human a ...
: A relatively low-level route through a range of mountains ; Milestone: One of a series of numbered markers placed along a road, often at regular intervals, showing the distance to destinations. ;National Highway: Road built and maintained by a national authority. ; Pavement: The road regarded as a geoconstruction. In the UK the term is
road surface A road surface (British English), or pavement (American English), 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, gravel road surfaces, hoggin, cobbles ...
and the pavement is a pedestrian walkway alongside the road. ;
Pedestrian crossing A pedestrian crossing (or crosswalk in American English) is a place designated for pedestrians to cross a road, street or avenue. The term "pedestrian crossing" is also used in the Vienna and Geneva Conventions, both of which pertain to road sig ...
: Designated point on a road where road marking or other means helps pedestrians cross safely ; Pelican crossing: (officially ''Pelicon crossing'') (UK) A PEdestrian LIght CONtrolled crossing. ; Private highway: Highway owned and operated for profit by
private industry The private sector is the part of the economy, sometimes referred to as the citizen sector, which is owned by private groups, usually as a means of establishment for profit or non profit, rather than being owned by the government. Employment The ...
; Private road: Road owned and maintained by a private individual, organization, or company rather than by a government ; Profile: The vertical alignment of a road, expressed as a series of grades, connected by parabolic curves. ; Protected Intersections for Bicycles :A much safer design with a corner refuge island, a setback crossing of the pedestrians and cyclists, generally between 1.5–7 metres of setback, a forward stop bar, which allows cyclists to stop for a traffic light well ahead of motor traffic who must stop behind the crosswalk. Separate signal staging or at least an advance green for cyclists and pedestrians is used to give cyclists and pedestrians no conflicts or a head start over traffic. The design makes a right turn on red, and sometimes left on red depending on the geometry of the intersection in question, possible in many cases, often without stopping. ; Protected Bicycle Path: Cyclists ideally have a protected bike lane on separated by a concrete median with splay kerbs if possible, and have a protected bike lane width of at least 2 metres if possible (one way). In the Netherlands, most one-way cycle paths are at least 2.5 metres wide. ; Public space: Place where anyone has a right to come without being excluded because of economic or social conditions ; Ranch road: U.S. road that connects rural and agricultural areas to market towns ; Road number: Often assigned to identify a stretch of public roads – often dependent on the
type of road A road is a thoroughfare, route, or way on land between two places that has been surfaced or otherwise improved to allow travel by foot or some form of conveyance, including a motor vehicle, cart, bicycle, or horse. Roads have been adapted to a ...
, with numbers differentiating between interstates, motorways,
arterial thoroughfares An arterial road or arterial thoroughfare is a high-capacity urban road that sits below freeways/motorways on the road hierarchy in terms of traffic flow and speed. The primary function of an arterial road is to deliver traffic from collector roa ...
, etc. ; Road-traffic safety: Process to reduce the harm (deaths, injuries, and property damage) that result from vehicle crashes on public roads ; Roadworks: 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 78 mph (126 km/h), waves with up to 350 m will excite motion sickness. ;
Roundabout A roundabout is a type of circular intersection or junction in which road traffic is permitted to flow in one direction around a central island, and priority is typically given to traffic already in the junction.''The New Shorter Oxford En ...
: 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 countries where traffic drives on the left the roundabout is traveled in a clockwise direction. Also known as an ''island'' in parts of the UK. ; Segregated Bicycle Path: Cyclists ideally have a protected bike lane separated by a concrete median with splay kerbs if possible, and have a protected bike lane width of at least 2 meters if possible (one way). In the Netherlands, most one-way cycle paths are at least 2.5 metres wide. ; Shoulder (also hard shoulder): A clear, level area to the side of the roadway available for stopping if needed. ;
State highway A state highway, state road, or state route (and the equivalent provincial highway, provincial road, or provincial route) is usually a road that is either ''numbered'' or ''maintained'' by a sub-national state or province. A road numbered by a ...
: Road numbered by the state, falling below numbered national highways (like
U.S. Routes The United States Numbered Highway System (often called U.S. Routes or U.S. Highways) is an integrated network of roads and highways numbered within a nationwide grid in the contiguous United States. As the designation and numbering of these hi ...
) in the hierarchy ''or'' a road maintained by the state, including nationally numbered highways ; Traffic: Pedestrians, ridden or herded animals, vehicles, bicycles, and other conveyances using any road for purposes of travel. ; Texture (roads): Deviations from a true planar pavement surface, which affects the interaction between road and tire. Microtexture have wavelengths below 0.5 mm, Macrotexture below 50 mm and Megatexture below 500 mm. ; Traffic calming: Set of strategies used by urban planners and traffic engineers to slow down or reduce motor vehicle traffic, thereby improving safety for pedestrians and bicyclists and improving the environment for residents ; Traffic 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 A roundabout is a type of circular intersection or junction in which road traffic is permitted to flow in one direction around a central island, and priority is typically given to traffic already in the junction.''The New Shorter Oxford En ...
in some parts of the UK ; Traffic light: Also known as a traffic signal, stop light, stop-and-go lights – a signaling device at a road intersection, pedestrian crossing, or other location that assigns right of way to different approaches to an intersection ; Zebra crossing (UK): A pedestrian crossing marked by black and white stripes on the carriageway


Construction

In transport engineering, subgrade is the native material underneath a constructed road. Road construction requires the creation of an
engineered Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad range of more specializ ...
continuous right-of-way or roadbed, overcoming geographic obstacles and having
grades Grade most commonly refers to: * Grade (education), a measurement of a student's performance * Grade, the number of the year a student has reached in a given educational stage * Grade (slope), the steepness of a slope Grade or grading may also r ...
low enough to permit vehicle or foot travel, and may be required to meet standards set by law or official guidelines. The process is often begun with the removal of earth and rock by digging or blasting, construction of embankments, bridges and tunnels, and removal of vegetation (this may involve deforestation) and followed by the laying of pavement material. A variety of road building equipment is employed in road building. After design, approval,
planning Planning is the process of thinking regarding the activities required to achieve a desired goal. Planning is based on foresight, the fundamental capacity for mental time travel. The evolution of forethought, the capacity to think ahead, is consi ...
, legal, and environmental considerations have been addressed alignment of the road is set out by a
surveyor Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is ca ...
. The radii and gradient are designed and staked out to best suit the natural ground levels and minimize the amount of cut and fill. Great care is taken to preserve reference Benchmarks Roads are designed and built for primary use by vehicular and pedestrian traffic.
Storm drain A storm drain, storm sewer (United Kingdom, United States, U.S. and Canada), surface water drain/sewer (United Kingdom), or stormwater drain (Australia and New Zealand) is infrastructure designed to Drainage, drain excess rain and ground water ...
age and environmental considerations are a major concern. Erosion and sediment controls are constructed to prevent detrimental effects. Drainage lines are laid with
sealed Seal may refer to any of the following: Common uses * Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly: ** Earless seal, or "true seal" ** Fur seal * Seal (emblem), a device to impr ...
joints in the road easement with runoff
coefficient In mathematics, a coefficient is a multiplicative factor in some term of a polynomial, a series, or an expression; it is usually a number, but may be any expression (including variables such as , and ). When the coefficients are themselves var ...
s and characteristics adequate for the land zoning and storm water system. Drainage systems must be capable of carrying the ultimate design flow from the upstream catchment with approval for the outfall from the appropriate authority to a watercourse,
creek A creek in North America and elsewhere, such as Australia, is a stream that is usually smaller than a river. In the British Isles it is a small tidal inlet. Creek may also refer to: People * Creek people, also known as Muscogee, Native Americans ...
, river or the sea for drainage discharge. A borrow pit (source for obtaining fill, gravel, and rock) and a water source should be located near or in reasonable distance to the road construction site. Approval from local authorities may be required to draw water or for working (crushing and screening) of materials for construction needs. The topsoil and vegetation is removed from the borrow pit and stockpiled for subsequent
rehabilitation Rehabilitation or Rehab may refer to: Health * Rehabilitation (neuropsychology), therapy to regain or improve neurocognitive function that has been lost or diminished * Rehabilitation (wildlife), treatment of injured wildlife so they can be retur ...
of the extraction area. Side slopes in the excavation area not steeper than one vertical to two horizontal for safety reasons. Old road surfaces, fences, and buildings may need to be removed before construction can begin. Trees in the road construction area may be marked for retention. These protected trees should not have the topsoil within the area of the tree's drip line removed and the area should be kept clear of construction material and equipment. Compensation or replacement may be required if a protected tree is damaged. Much of the vegetation may be
mulched A mulch is a layer of material applied to the surface of soil. Reasons for applying mulch include conservation of soil moisture, improving fertility and health of the soil, reducing weed growth and enhancing the visual appeal of the area. A mu ...
and put aside for use during reinstatement. The topsoil is usually stripped and stockpiled nearby for rehabilitation of newly constructed embankments along the road. Stumps and roots are removed and holes filled as required before the earthwork begins. Final rehabilitation after road construction is completed will include seeding, planting, watering and other activities to reinstate the area to be consistent with the untouched surrounding areas. 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 meet the design requirements (generally 90–95% relative compaction). Blasting is not frequently used to excavate the roadbed as the intact rock structure forms an ideal road base. 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, under saturated conditions. The process is repeated until the desired grade is reached. General
fill material Fill dirt (also called cleanfill, or just fill) 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.organics, meet minimum California bearing ratio (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 ( sieved) should be composed of
gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifi ...
, decomposed rock or broken rock below a specified particle size and be free of large lumps of clay. Sand clay fill may also be used. The roadbed must be "proof rolled" after each layer of fill is compacted. If a
roller Roller may refer to: Birds *Roller, a bird of the family Coraciidae * Roller (pigeon), a domesticated breed or variety of pigeon Devices * Roller (agricultural tool), a non-powered tool for flattening ground * Road roller, a vehicle for compa ...
passes over an area without creating visible deformation or spring the section is deemed to comply. Geosynthetics such as geotextiles, geogrids, and
geocells Cellular confinement systems (CCS)—also known as geocells—are widely used in construction for erosion control, soil stabilization on flat ground and steep slopes, channel protection, and structural reinforcement for load support and earth r ...
are frequently used in the various pavement layers to improve road quality. These materials and methods are used in low-traffic private roadways as well as public roads and highways.Step by Step Guide: How to Lay a Gravel Driveway , Mainland Ltd
Gravel Driveway Construction''] at www.mainlandaggregates.co.uk. Retrieved 25 Jan 2015
Geosynthetics perform four main functions in roads: separation, reinforcement, filtration, and drainage; which increase the pavement performance, reduce construction costs and decrease maintenance. The completed roadway is finished by paving or left with a gravel or other Dirt road, natural surface. The
type of road A road is a thoroughfare, route, or way on land between two places that has been surfaced or otherwise improved to allow travel by foot or some form of conveyance, including a motor vehicle, cart, bicycle, or horse. Roads have been adapted to a ...
surface is dependent on economic factors and expected usage. Safety improvements such as traffic signs, crash barriers, raised pavement markers and other forms of road surface marking 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 road is converted into dual carriageway 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 to
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 In the earliest days of railways in the United Kingdom, most lin ...
, the new carriageway is not always constructed directly alongside the existing carriageway.


Reallocation

Roads that are intended for use by a particular mode of transport can be reallocated for another mode of transport, i.e. by using traffic signs. For instance, in the ongoing road space reallocation effort, some roads (particularly in city centers) which are intended for use by
car A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarded as ...
s are increasingly being repurposed for cycling and/or walking.


Maintenance

Like all structures, roads deteriorate over time. Deterioration is primarily due to environmental effects such as frost heaves, thermal cracking and oxidation often contribute, however accumulated damage from vehicles also contributes. According to a series of experiments carried out in the late 1950s, called the AASHO Road Test, it was empirically determined that the effective damage done to the road is roughly proportional to the fourth power of axle weight. A typical tractor-trailer weighing 80,000 pounds (36.287 t) 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 with 2,000 pounds (0.907 t) on each axle.
Pothole A pothole is a depression in a road surface, usually asphalt pavement, where traffic has removed broken pieces of the pavement. It is usually the result of water in the underlying soil structure and traffic passing over the affected area. Water ...
s on roads are caused by rain damage and vehicle braking or related construction works. Pavements are designed for an expected service life or design life. In some parts of the United Kingdom the standard design life is 40 years for new
bitumen Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term a ...
and concrete pavement. Maintenance is considered in the whole life cost of the road with service at 10, 20 and 30 year milestones. Roads can be and are designed for a variety of lives (8-, 15-, 30-, and 60-year designs). When pavement lasts longer 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. Some asphalt pavements are designed as ''perpetual pavements'' with an expected structural life in excess of 50 years. Many asphalt pavements built over 35 years ago, despite not being specifically designed as a perpetual pavement, have remained in good condition long past their design life. Many concrete pavements built since the 1950s have significantly outlived their intended design lives. Some roads like Chicago, Illinois's Wacker Drive, a major two-level (and at one point, three-level) roadway in the 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 is the process of planning the maintenance and repair of a network of roadways or other paved facilities in order to optimize pavement conditions over the entire network. It is also applied to airport runways and ocean freight ...
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 A profilometer is a measuring instrument used to measure a surface's profile, in order to quantify its roughness. Critical dimensions as step, curvature, flatness are computed from the surface topography. While the historical notion of a pro ...
s. These measurements include road
curvature In mathematics, curvature is any of several strongly related concepts in geometry. Intuitively, the curvature is the amount by which a curve deviates from being a straight line, or a surface deviates from being a plane. For curves, the canonic ...
, cross slope, asperity, roughness, rutting and texture. Software algorithms use this data to recommend maintenance or new construction. Maintenance treatments for asphalt concrete generally include thin asphalt overlays, crack sealing, surface rejuvenating, fog sealingfo, micro milling or diamond grinding and surface treatments. Thin surfacing preserves, protects and improves the functional condition of the road while reducing the need for routing maintenance, leading to extended service life without increasing structural capacity. Older concrete pavements that develop faults can be repaired with a dowel bar retrofit, in which slots are cut in the pavement at each joint, and dowel bars are placed in the slots, which are then filled with concrete patching material. This can extend the life of the concrete pavement for 15 years. 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 (US) about 50% of the roads in the US 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 Infiltration may refer to: Science, medicine, and engineering *Infiltration (hydrology), downward movement of water into soil *Infiltration (HVAC), a heating, ventilation, and air conditioning term for air leakage into buildings *Infiltration (me ...
. 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) 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 cementitious
grout Grout is a dense fluid which hardens to fill gaps or used as reinforcement in existing structures. Grout is generally a mixture of water, cement and sand, and is employed in pressure grouting, embedding rebar in masonry walls, connecting secti ...
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 the 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 used 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 A rotary hammer, also called rotary hammer drill is a power tool that can perform heavy-duty tasks such as drilling and chiseling hard materials. It is similar to a hammer drill in that it also pounds the drill bit in and out while it is spinni ...
. Next, a two-part
epoxy Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also coll ...
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 Spall are fragments of a material that are broken off a larger solid body. It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ball ...
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. Minnesota DOT


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) 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 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 system from traffic collisions. On neighborhood roads traffic calming, safety barriers, pedestrian crossings and cycle lanes can help protect pedestrians, cyclists, and drivers. Lane markers in some countries and states are marked with
Cat's eyes Cat's Eyes are an alternative pop duo formed in early 2011 by vocalist Faris Badwan (known for his work with English indie rock band the Horrors) and Italian-Canadian soprano, composer and multi-instrumentalist Rachel Zeffira. History The band ...
or Botts dots, (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 A limited-access road, known by various terms worldwide, including limited-access highway, dual-carriageway, expressway, limited access freeway, and partial controlled access highway, is a highway or arterial road for high-speed traffic which ...
from properties and local roads, grade separated junctions and median dividers between opposite-direction traffic to reduce the 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 Street furniture is a collective term for objects and pieces of equipment installed along streets and roads for various purposes. It includes benches, traffic barriers, bollards, post boxes, phone boxes, streetlamps, traffic lights, traff ...
such as road signs and
fire hydrants A fire hydrant, waterplug, or firecock (archaic) is a connection point by which firefighters can tap into a water supply. It is a component of active fire protection. Underground fire hydrants have been used in Europe and Asia since at least ...
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. During heavy rains, if the elevation of the road surface isn't higher than the surrounding landscape, it may result in flooding. Speed limits can improve road traffic safety and reduce the number of road traffic casualties from traffic collisions. In their ''World report on road traffic injury prevention'' report, the World Health Organization (WHO) identify speed control as one of various interventions likely to contribute to a reduction in road casualties.


Road conditions

Road conditions are the collection of factors describing the ease of driving on a particular stretch of road, or on the roads of a particular locality, including the quality of the pavement surface,
pothole A pothole is a depression in a road surface, usually asphalt pavement, where traffic has removed broken pieces of the pavement. It is usually the result of water in the underlying soil structure and traffic passing over the affected area. Water ...
s, road markings, and weather. It has been reported that " oblems of transportation participants and road conditions are the main factors that lead to road traffic accidents". It has further been specifically noted that "weather conditions and road conditions are interlinked as weather conditions affect the road conditions". Specific aspects of road conditions can be of particular importance for particular purposes. For example, for autonomous vehicles such as self-driving cars, significant road conditions can include "shadowing and lighting changes, road surface texture changes, and road markings consisting of circular reflectors, dashed lines, and solid lines". Various government agencies and private entities, including local news services, track and report on road conditions to the public so that drivers going through a particular area can be aware of hazards that may exist in that area. News agencies, in turn, rely on tips from area residents with respect to certain aspects of road conditions in their coverage area.


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 running off of roads tends to pick up gasoline,
motor oil Motor oil, engine oil, or engine lubricant is any one of various substances used for the lubrication of internal combustion engines. They typically consist of base oils enhanced with various additives, particularly antiwear additives, deterg ...
,
heavy metals upright=1.2, Crystals of osmium, a heavy metal nearly twice as dense as lead">lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead Heavy metals are generally defined as ...
, trash and other pollutants and result in water pollution. Road runoff is a major source of nickel, copper, zinc, cadmium, lead and polycyclic aromatic hydrocarbons (PAHs), which are created as combustion byproducts of gasoline and other
fossil fuel A fossil fuel is a hydrocarbon-containing material formed naturally in the Earth's crust from the remains of dead plants and animals that is extracted and burned as a fuel. The main fossil fuels are coal, oil, and natural gas. Fossil fuels m ...
s. De-icing chemicals and sand can run off into roadsides, contaminate groundwater and pollute
surface water Surface water is water located on top of land forming terrestrial (inland) waterbodies, and may also be referred to as ''blue water'', opposed to the seawater and waterbodies like the ocean. The vast majority of surface water is produced by prec ...
s; and road salts can be toxic to sensitive plants and animals. Sand applied to icy roads can be ground up by traffic into fine particulates and contribute to air pollution. Roads are a chief source of noise pollution. In the early 1970s, it was recognized that design of roads can be conducted to influence and minimize noise generation.
Noise barrier A noise barrier (also called a soundwall, noise wall, sound berm, sound barrier, or acoustical barrier) is an exterior structure designed to protect inhabitants of sensitive land use areas from noise pollution. Noise barriers are the most effecti ...
s can reduce noise pollution near built-up areas. Regulations can restrict the use of engine braking. Motor vehicle emissions 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. In addition, on-road transportation greenhouse gas emissions are the largest single cause of climate change, scientists say.


Regulation


Right- and left-hand traffic

Traffic flows on the right or on the left side of the road depending on the country. In countries where traffic flows on the right, traffic signs are mostly on the right side of the road,
roundabout A roundabout is a type of circular intersection or junction in which road traffic is permitted to flow in one direction around a central island, and priority is typically given to traffic already in the junction.''The New Shorter Oxford En ...
s and traffic circles go counter-clockwise/anti-clockwise, and pedestrians crossing a two-way road should watch out for traffic from the left first. In countries where traffic flows on the left, the reverse is true. About 33% of the world by population 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 is used to understand both the relationship between the transport system and the wider economy and the complex network effects when there are multiple paths and competing modes for both personal and freight (road/rail/air/ferry) and where induced demand 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 using taxation although implementation may be through
private Private or privates may refer to: Music * " In Private", by Dusty Springfield from the 1990 album ''Reputation'' * Private (band), a Denmark-based band * "Private" (Ryōko Hirosue song), from the 1999 album ''Private'', written and also recorde ...
contractors). or occasionally using
road tolls A toll is a fee charged for the use of a road or waterway. History Tolls usually had to be paid at strategic locations such as bridges (sometimes called a bridge toll) or gates. In Europe, the road toll goes back to the practice of the Germ ...
. Public-private partnerships are a way for communities to address the rising cost by injecting private funds into the infrastructure. There are four main ones: * design/build * design/build/operate/maintain * design/build/finance/operate * build/own/operate Society depends heavily on efficient roads. In the European Union (EU) 44% of all goods are moved by trucks over roads and 85% of all people are transported by cars, buses or coaches on roads. The term was also commonly used to refer to
roadstead A roadstead (or ''roads'' – the earlier form) is a body of water sheltered from rip currents, spring tides, or ocean swell where ships can lie reasonably safely at anchor without dragging or snatching.United States Army technical manual, TM 5- ...
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 The New Jersey Turnpike (NJTP) is a system of controlled-access highways in the U.S. state of New Jersey. The turnpike is maintained by the New Jersey Turnpike Authority (NJTA).The Garden State Parkway, although maintained by NJTA, is not consi ...
– $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 has the largest network of roads of any country with as of 2009. The Republic of India has the second-largest road system globally with 4,689,842 kilometres (2,914,133 mi) of road (2013). The People's Republic of China is third with of road (2007). The Federative Republic of Brazil has the fourth-largest road system in the world with (2002). See List of countries by road network size. When looking only at
expressways Expressway may refer to: *Controlled-access highway, the highest-grade type of highway with access ramps, lane markings, etc., for high-speed traffic. *Limited-access road, a lower grade of highway or arterial road. *Expressway, the fictional slide ...
, the National Trunk Highway System (NTHS) in China has a total length of at the end of 2006, and 60,300 km at the end of 2008, second only to the United States with in 2005. However, as of 2017, China has 130,000 km of Expressways.


Global connectivity

Eurasia, Africa, North America, South America, and Australia each have an extensive road network that connects most cities. The North and South American road networks are separated by the Darién Gap, the only interruption in the Pan-American Highway. Eurasia and Africa are connected by roads on the Sinai Peninsula. The
European Peninsula Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...
is connected to the
Scandinavian Peninsula The Scandinavian Peninsula ( sv, Skandinaviska halvön; no, Den skandinaviske halvøy (Bokmål) or nn, Den skandinaviske halvøya; fi, Skandinavian niemimaa) is a peninsula located in Northern Europe, which roughly comprises the mainlands ...
by the Øresund Bridge, and both have many connections to the mainland of Eurasia, including the bridges over the
Bosphorus The Bosporus Strait (; grc, Βόσπορος ; tr, İstanbul Boğazı 'Istanbul strait', colloquially ''Boğaz'') or Bosphorus Strait is a natural strait and an internationally significant waterway located in Istanbul in northwestern Tu ...
. Antarctica has very few roads and no continent-bridging network, though there are a few ice roads between bases, such as the
South Pole Traverse The South Pole Traverse, also called the South Pole Overland Traverse, is an approximately flagged route over compacted snow and ice in Antarctica that links McMurdo Station on the coast to the Amundsen–Scott South Pole Station, both operated ...
. Bahrain is the only island country to be connected to a continental network by road (the King Fahd Causeway to Saudi Arabia). Even well-connected road networks are controlled by many different legal jurisdictions, and laws such as which side of the road to drive on vary accordingly. Many populated domestic islands are connected to the mainland by bridges. A very long example is the Overseas Highway connecting many of the
Florida Keys The Florida Keys are a coral cay archipelago located off the southern coast of Florida, forming the southernmost part of the continental United States. They begin at the southeastern coast of the Florida peninsula, about south of Miami, and e ...
with the continental United States. Even on mainlands, some settlements have no roads connecting with the primary continental network, due to natural obstacles like mountains or wetlands, or high cost compared to the population served. Unpaved roads or lack of roads are more common in developing countries, and these can become impassible in wet conditions. As of 2014, only 43% of rural Africans have access to an all-season road. Due to steepness, mud, snow, or fords, roads can sometimes be passable only to four-wheel drive vehicles, those with
snow chain Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout ...
s or snow tires, or those capable of
deep wading Deep wading or deep fording is a technique used by some heavy semi-amphibious vehicles to traverse water that is several metres deep - the vehicle drives on the riverbed/lakebed/seabed and uses screens or a pipe (a snorkel) that reaches above the ...
or amphibious operation. Most disconnected settlements have local road networks connecting ports, buildings, and other points of interest. Where demand for travel by road vehicle to a disconnected island or mainland settlement is high, roll-on/roll-off ferries are commonly available if the journey is relatively short. For long-distance trips, passengers usually travel by air and rent a car upon arrival. If facilities are available, vehicles and cargo can also be shipped to many disconnected settlements by boat, or air transport at much greater expense. The island of Great Britain is connected to the European road network by Eurotunnel Shuttle – an example of a car shuttle train which is a service used in other parts of Europe to travel under mountains and over wetlands. In polar areas, disconnected settlements are often more easily reached by snowmobile or dogsled in cold weather, which can produce
sea ice Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oce ...
that blocks ports, and bad weather that prevents flying. For example, resupply aircraft are only flown to
Amundsen–Scott South Pole Station The Amundsen–Scott South Pole Station is the United States scientific research station at the South Pole of the Earth. It is the southernmost point under the jurisdiction (not sovereignty) of the United States. The station is located on the ...
October to February, and many residents of coastal Alaska have bulk cargo shipped in only during the warmer months. Permanent darkness during the winter can also make long-distance travel more dangerous in polar areas. Continental road networks do reach into these areas, such as the Dalton Highway to the North Slope of Alaska, the R21 highway to Murmansk in Russia, and many roads in Scandinavia (though due to fjords water transport is sometimes faster). Large areas of Alaska, Canada, Greenland, and Siberia are sparsely connected. For example, all 25 communities of
Nunavut Nunavut ( , ; iu, ᓄᓇᕗᑦ , ; ) is the largest and northernmost Provinces and territories of Canada#Territories, territory of Canada. It was separated officially from the Northwest Territories on April 1, 1999, via the ''Nunavut Act'' ...
are disconnected from each other and the main North American road network. Road transport of people and cargo by may also be obstructed by
border control Border control refers to measures taken by governments to monitor and regulate the movement of people, animals, and goods across land, air, and maritime borders. While border control is typically associated with international borders, it a ...
s and travel restrictions. For example, travel from other parts of Asia to South Korea would require passage through the hostile country of North Korea. Moving between most countries in Africa and Eurasia would require passing through Egypt and Israel, which is a politically sensitive area. Some places are intentionally car-free, and roads (if present) might be used by bicycles or pedestrians. Roads are under construction to many remote places, such as the villages of the Annapurna Circuit, and a road was completed in 2013 to Mêdog County. Additional intercontinental and transoceanic fixed links have been proposed, including a Bering Strait crossing that would connect Eurasia-Africa and North America, a Malacca Strait Bridge to the largest island of Indonesia from Asia, and a
Strait of Gibraltar crossing The Strait of Gibraltar crossing is a hypothetical bridge or tunnel spanning the Strait of Gibraltar (about 14 km or 9 miles at its narrowest point) that would connect Europe and Africa. The governments of Spain and Morocco appointed a joi ...
to connect Europe and Africa directly.


See also


References

{{Authority control Infrastructure Types of roads