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A road is a linear way for the conveyance of
traffic Traffic comprises pedestrians, vehicles, ridden or herded animals, trains, and other conveyances that use public ways (roads) for travel and transportation. Traffic laws govern and regulate traffic, while rules of the road include 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,
avenue Avenue or Avenues may refer to: Roads * Avenue (landscape), traditionally a straight path or road with a line of trees, in the shifted sense a tree line itself, or some of boulevards (also without trees) * Avenue Road, Bangalore * Avenue Road, ...
s,
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),
tollway A toll road, also known as a turnpike or tollway, is a public or private road (almost always a controlled-access highway in the present day) for which a fee (or ''toll'') is assessed for passage. It is a form of road pricing typically implemented ...
s,
interstate The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate Highway System, is a network of controlled-access highways that forms part of the National Highway System in the United States. Th ...
s,
highway A highway is any public or private road or other public way on land. It is used for major roads, but also includes other public roads and public tracks. In some areas of the United States, it is used as an equivalent term to controlled-access ...
s,
thoroughfare A thoroughfare is a primary passage or way as a transit route through regularly trafficked areas, whether by road on dry land or, by extension, via watercraft or aircraft. On land, a thoroughfare may refer to anything from a multi-lane highway ...
s, and local roads. The primary features of roads include
lane In road transport, a lane is part of a roadway that is designated to be used by a single line of vehicles to control and guide drivers and reduce traffic conflicts. Most public roads (highways) have at least two lanes, one for traffic in each ...
s,
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),
roadway A carriageway (British English) or roadway (North American English) consists of a width of road on which a vehicle is not restricted by any physical barriers or separation to move laterally. A carriageway generally consists of a number of tra ...
s (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 The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder mak ...
, verges,
bike path A bike path is a bikeway separated from motorized traffic and dedicated to cycling or shared with pedestrians or other non-motorized users. In the US a bike path sometimes encompasses ''shared use paths'', "multi-use path", or "Class III bikewa ...
s (cycle paths), and
shared-use path A shared-use path, mixed-use path or multi-use pathway is a path which is 'designed to accommodate the movement of pedestrians and cyclists'. Examples of shared-use paths include sidewalks designated as shared-use, bridleways and rail trails. A ...
s.


Definitions

Historically many roads were simply recognizable routes without any formal construction or some maintenance. The Organization for Economic Co-operation and Development (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 The United Nations Economic Commission for Europe (ECE or UNECE) is one of the five regional commissions under the jurisdiction of the United Nations Economic and Social Council. It was established in order to promote economic cooperation and i ...
''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 The Convention on Road Traffic, commonly known as the Vienna Convention on Road Traffic, is an international treaty designed to facilitate international road traffic and to increase road safety by establishing standard traffic rules among the co ...
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 An easement is a nonpossessory right to use and/or enter onto the real property of another without possessing it. It is "best typified in the right of way which one landowner, A, may enjoy over the land of another, B". An easement is a propert ...
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 The Highways Act 1980 (1980 c.66) 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. Man ...
, which covers
England and Wales England and Wales () is one of the three legal jurisdictions of the United Kingdom. It covers the constituent countries England and Wales and was formed by the Laws in Wales Acts 1535 and 1542. The substantive law of the jurisdiction is Eng ...
but not
Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...
or
Northern Ireland Northern Ireland ( ga, Tuaisceart Éireann ; sco, label= Ulster-Scots, Norlin Airlann) is a part of the United Kingdom, situated in the north-east of the island of Ireland, that is variously described as a country, province or region. Nort ...
, 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 Vehicle Excise Duty (VED; also known as "vehicle tax", "car tax", and more controversially as "road tax", and formerly as a "tax disc") is an annual tax that is levied as an excise duty and which must be paid for most types of powered vehicles which ...
, 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 A motor vehicle, also known as motorized vehicle or automotive vehicle, is a self-propelled land vehicle, commonly wheeled, that does not operate on Track (rail transport), rails (such as trains or trams) and is used for the transportation of pe ...
, 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
trail A trail, also known as a path or track, is an unpaved lane or small road usually passing through a natural area. In the United Kingdom and the Republic of Ireland, a path or footpath is the preferred term for a pedestrian or hiking trail. Th ...
s 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 The Icknield Way is an ancient trackway in southern and eastern England that runs from Norfolk to Wiltshire. It follows the chalk escarpment that includes the Berkshire Downs and Chiltern Hills. Background It is generally said to be, within ...
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 In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, chemical composition, and the way in which it is formed. Rocks ...
-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 Glastonbury (, ) is a town and civil parish in Somerset, England, situated at a dry point on the low-lying Somerset Levels, south of Bristol. The town, which is in the Mendip district, had a population of 8,932 in the 2011 census. Glastonbury ...
, England. * The
Sweet Track The Sweet Track is an ancient trackway, or causeway, in the Somerset Levels, England, named after its finder, Ray Sweet. It was built in 3807 BC (determined using dendrochronology) and is the second-oldest timber trackway discovered in ...
, 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 Darius I ( peo, 𐎭𐎠𐎼𐎹𐎺𐎢𐏁 ; grc-gre, Δαρεῖος ; – 486 BCE), commonly known as Darius the Great, was a Persian ruler who served as the third King of Kings of the Achaemenid Empire, reigning from 522 BCE until his d ...
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 The Royal Road was an ancient highway reorganized and rebuilt by the Persian king Darius the Great (Darius I) of the first (Achaemenid) Persian Empire in the 5th century BC. Darius built the road to facilitate rapid communication on the western ...
, which was one of the finest highways of its time, connecting
Sardis Sardis () or Sardes (; Lydian: 𐤳𐤱𐤠𐤭𐤣 ''Sfard''; el, Σάρδεις ''Sardeis''; peo, Sparda; hbo, ספרד ''Sfarad'') was an ancient city at the location of modern ''Sart'' (Sartmahmut before 19 October 2005), near Salihli, ...
(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 India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
. * 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
barge Barge nowadays generally refers to a flat-bottomed inland waterway vessel which does not have its own means of mechanical propulsion. The first modern barges were pulled by tugs, but nowadays most are pushed by pusher boats, or other vessels ...
s. A hybrid of road transport and ship transport beginning in about 1740 is the
horse-drawn boat A horse-drawn boat or tow-boat is a historic boat operating on a canal, pulled by a horse walking beside the canal on a towpath. United Kingdom The Romans are known to have used mules to haul boats on their waterways in the UK. Boat horses were t ...
in which the horse follows a cleared path along the river bank. * From about 312 BC, the
Roman Empire The Roman Empire ( la, Imperium Romanum ; grc-gre, Βασιλεία τῶν Ῥωμαίων, Basileía tôn Rhōmaíōn) was the post-Republican period of ancient Rome. As a polity, it included large territorial holdings around the Mediterr ...
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 , established_title = Founded , established_date = 753 BC , founder = King Romulus (legendary) , image_map = Map of comune of Rome (metropolitan city of Capital Rome, region Lazio, Italy).svg , map_caption ...
and covering 78,000 kilometers or 52,964
Roman mile The mile, sometimes the international mile or statute mile to distinguish it from other miles, is a British imperial unit and United States customary unit of distance; both are based on the older English unit of length equal to 5,280 Engli ...
s of paved roads. * In the 8th century AD, many roads were built throughout the Arab Empire. The most sophisticated roads were those in
Baghdad Baghdad (; ar, بَغْدَاد , ) is the capital of Iraq and the second-largest city in the Arab world after Cairo. It is located on the Tigris near the ruins of the ancient city of Babylon and the Sassanid Persian capital of Ctesiphon ...
, which were paved with
tar Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat. "a dark brown or black bit ...
. 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 Destruction may refer to: Concepts * Destruktion, a term from the philosophy of Martin Heidegger * Destructive narcissism, a pathological form of narcissism * Self-destructive behaviour, a widely used phrase that ''conceptualises'' certain kind ...
. * The
Highways Act 1555 The Highways Act 1555 (2 & 3 Ph. & Mary, c. 8), sometimes the First Statute of Highways, was an Act of the Parliament of England, which placed the burden of upkeep of the highways on individual parishes and that was passed in 1555. The Act wa ...
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 trust Turnpike trusts were bodies set up by individual Acts of Parliament in the United Kingdom, acts of Parliament, with powers to collect road toll road, tolls for maintaining the principal roads in Kingdom of Great Britain, Britain from the 17th b ...
s 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 The Rebecca Riots (Welsh: ''Terfysgoedd Beca'') took place between 1839 and 1843 in West and Mid Wales. They were a series of protests undertaken by local farmers and agricultural workers in response to levels of taxation. The rioters, often me ...
in Carmarthenshire and
Rhayader Rhayader (; cy, Rhaeadr Gwy; ) is a market town and community in Powys, Wales, within the historic county of Radnorshire. The town is from the source of the River Wye on Plynlimon, the highest point of the Cambrian Mountains, and is locate ...
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 between
Duino Duino ( sl, Devin, german: Tybein) is today a seaside resort on the northern Adriatic coast. It is a ''hamlet'' of Duino-Aurisina, a municipality (''comune'') of the Friuli–Venezia Giulia region of northeastern Italy. The settlement, picturesque ...
and
Barcola Barcola is a maritime neighbourhood of Trieste, Italy. It is a popular tourist place with beaches and long promenades, near the Habsburg-established Miramare Castle. Barcola is highly valued for the high quality of life and the free access to the ...
in 1928 was very much focused on creating jobs.


Design

Road design is part of
highway engineering Highway engineering is an engineering discipline branching from civil engineering that involves the planning, design, construction, operation, and maintenance of roads, bridges, and tunnels to ensure safe and effective transportation of people and ...
.
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 (e.g. 10,000,000) divided in groups (e.g. trucks, vans, ...
is designing a road for the environment in order to extend its longevity and reduce maintenance. The
Shell pavement design method The Shell pavement design method was used in many countries for the design of new pavements made of asphalt. First published in 1963, it was the first mechanistic design method, providing a procedure that was no longer based on codification of histo ...
is used in many countries for the design of new asphalt roadsides.


Terminology

;
Adverse camber The cant of a railway track or camber of a road (also referred to as superelevation, cross slope or cross fall) is the rate of change in elevation (height) between the two rails or edges. This is normally greater where the railway or road is curv ...
: 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 A banked turn (or banking turn) is a turn or change of direction in which the vehicle banks or inclines, usually towards the inside of the turn. For a road or railroad this is usually due to the roadbed having a transverse down-slope towards the ...
;
Belisha Beacon A Belisha beacon is an amber-coloured globe lamp atop a tall black and white striped pole, marking pedestrian crossings of roads in the United Kingdom, Ireland, and in other countries historically influenced by Britain such as Hong Kong, Malta ...
: An orange globe, lit at night, used to highlight a pedestrian crossing ;
Bicycle boulevard A bicycle boulevard, sometimes referred to as a neighborhood greenway, neighborway, neighborhood bikeway or neighborhood byway is a type of bikeway composed of a low-speed street which has been "optimized" for bicycle traffic. Bicycle boulevar ...
: 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: Road that avoids or "bypasses" a built-up area, town, or village ;
Bottleneck Bottleneck literally refers to the narrowed portion (neck) of a bottle near its opening, which limit the rate of outflow, and may describe any object of a similar shape. The literal neck of a bottle was originally used to play what is now known as ...
: Section of a road with a carrying capacity substantially below that of other sections of the same road ; Botts' dots: Non-reflective
raised pavement marker A raised pavement marker is a safety device used on roads. These devices are usually made with plastic, ceramic, thermoplastic paint, glass or occasionally metal, and come in a variety of shapes and colors. Raised reflective markers, such as ...
used on roads ;
Camber Camber may refer to a variety of curvatures and angles: * Camber angle, the angle made by the wheels of a vehicle * Camber beam, an upward curvature of a joist to compensate for load deflection due in buildings * Camber thrust in bike technology * ...
(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 Cant, CANT, canting, or canted may refer to: Language * Cant (language), a secret language * Beurla Reagaird, a language of the Scottish Highland Travellers * Scottish Cant, a language of the Scottish Lowland Travellers * Shelta or the Cant, a la ...
: Another name for cross slope or camber ;
Carriageway A carriageway (British English) or roadway (North American English) consists of a width of road on which a vehicle is not restricted by any physical barriers or separation to move laterally. A carriageway generally consists of a number of tra ...
: 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 Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves. The ' ...
raised pavement marker A raised pavement marker is a safety device used on roads. These devices are usually made with plastic, ceramic, thermoplastic paint, glass or occasionally metal, and come in a variety of shapes and colors. Raised reflective markers, such as ...
used on roads ;
Chicane A chicane () is a serpentine curve in a road, added by design rather than dictated by geography. Chicanes add extra turns and are used both in motor racing and on roads and streets to slow traffic for safety. For example, one form of chicane is ...
: Sequence of tight serpentine curves (usually an S-shape curve or a bus stop) ;
Chipseal Chipseal (also chip seal or chip and seal) is a pavement surface treatment that combines one or more layer(s) of asphalt with one or more layer(s) of fine aggregate. In the United States, chipseals are typically used on rural roads carrying low ...
: 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 A corniche is a road on the side of a cliff or mountain, with the ground rising on one side and falling away on the other. The word has been absorbed into English from the French term ' or "road on a ledge", originally derived from the Itali ...
: Road on the side of a cliff or mountain, with the ground rising on one side and falling away on the other ;
Cross slope Cross slope, cross fall or camber is a geometric feature of pavement surfaces: the transverse slope with respect to the horizon. It is a very important safety factor. Cross slope is provided to provide a drainage gradient so that water will run o ...
: The
slope In mathematics, the slope or gradient of a line is a number that describes both the ''direction'' and the ''steepness'' of the line. Slope is often denoted by the letter ''m''; there is no clear answer to the question why the letter ''m'' is use ...
of the pavement, expressed as units of rise per unit of run, or as a percentage ;
Curb A curb (North American English), or kerb (Commonwealth English except Canada; see spelling differences), is the edge where a raised sidewalk or road median/central reservation meets a street or other roadway. History Although curbs have ...
(kerb): A raised edge at the side of the
roadway A carriageway (British English) or roadway (North American English) consists of a width of road on which a vehicle is not restricted by any physical barriers or separation to move laterally. A carriageway generally consists of a number of tra ...
. ;
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 Traffic calming uses physical design and other measures to improve safety for motorists, pedestrians and bicycle-friendly, cyclists. It has become a tool to combat speeding and other unsafe behaviours of drivers in the neighbourhoods. It aims ...
measure, intended to slow the speed of traffic and increase driver awareness, particularly in built-up and residential
neighborhoods A neighbourhood (British English, Irish English, Australian English and Canadian English) or neighborhood (American English; American and British English spelling differences, see spelling differences) is a geographically localised community ...
. ;
Cycle lane Cycle, cycles, or cyclic may refer to: Anthropology and social sciences * Cyclic history, a theory of history * Cyclical theory, a theory of American political history associated with Arthur Schlesinger, Sr. * Social cycle, various cycles in so ...
: 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 A cycle track, separated bike lane or protected bike lane (sometimes historically referred to as a sidepath) is an exclusive bikeway that has elements of a separated path and on-road bike lane. A cycle track is located within or next to the ro ...
: 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 Drainage gradient (DG) is a term in road design, defined as the combined slope due to road surface cross slope (CS) and longitudinal slope (hilliness). Although the term may not be used, the concept is also used in roof design and landscape arc ...
;
Farm-to-market road In the United States, a farm-to-market road or ranch-to-market road (sometimes farm road or ranch road for short) is a state highway or county road that connects rural or agricultural areas to market towns. These are better quality roads, usually ...
: A state road or county road that connects rural or agricultural areas to market towns. ;
Fork In cutlery or kitchenware, a fork (from la, furca 'pitchfork') is a utensil, now usually made of metal, whose long handle terminates in a head that branches into several narrow and often slightly curved tines with which one can spear foods ei ...
: (literally "fork in the road") Type of intersection where a road splits ;
Grade 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 ref ...
: 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 A guide rail is a device or mechanism to direct products, vehicles or other objects through a channel, conveyor, roadway or rail system. Several types of guide rails exist and may be associated with: * Factory or production line conveyors * Pow ...
: 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 Traffic barriers (sometimes called Armco barriers,AK Steel (formerly Armco) genericized trademark also known in North America as guardrails or guard rails and in Britain as crash barriers) keep vehicles within their roadway and prevent them from ...
. ;
Gutter Gutter may refer to: Water discharge structures * Rain gutter, used on roofs and in buildings * Street gutter, for drainage of streets Design and printing * Gutter, in typography, the space between columns of printed text * Gutter, in bookbi ...
: A drainage channel usually at the edge of the road or along a median. ;
Interstate Highway System The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate Highway System, is a network of controlled-access highways that forms part of the National Highway System in the United States. Th ...
(United States): System of Interstate and Defense Highways ;
Lane In road transport, a lane is part of a roadway that is designated to be used by a single line of vehicles to control and guide drivers and reduce traffic conflicts. Most public roads (highways) have at least two lanes, one for traffic in each ...
: 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 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 Loose chippings are loose gravel or stone fragments on a road surface and form a hazard to vehicles using that road. It may come from the road's chip seal. Causes include: * Unbound surplus aggregate not removed from the surface when the road is r ...
: 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 highway 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 ...
s 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 British English (BrE, en-GB, or BE) is, according to Lexico, Oxford Dictionaries, "English language, English as used in Great Britain, as distinct from that used elsewhere". More narrowly, it can refer specifically to the English language in ...
), median (
North American English North American English (NAmE, NAE) is the most generalized variety of the English language as spoken in the United States and Canada. Because of their related histories and cultures, plus the similarities between the pronunciations (accents), v ...
), 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
lane In road transport, a lane is part of a roadway that is designated to be used by a single line of vehicles to control and guide drivers and reduce traffic conflicts. Most public roads (highways) have at least two lanes, one for traffic in each ...
s of traffic ;
Motorway 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 ...
: (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 A milestone is a numbered marker placed on a route such as a road, railway line, canal or boundary. They can indicate the distance to towns, cities, and other places or landmarks; or they can give their position on the route relative to so ...
: 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 A pelican crossing, or archaically pelicon crossing (PEdestrian LIght CONtrolled), is a type of pedestrian crossing with traffic signals for both pedestrians and vehicular traffic, activated by call buttons for pedestrians, with the walk signal ...
: (officially ''Pelicon crossing'') (UK) A PEdestrian LIght CONtrolled crossing. ;
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. Typically, private highways are bu ...
: Highway owned and operated for profit by private industry ;
Private road A private road is a road owned or controlled by a private person, persons or corporation rather than a road open to the public and owned by a government. Private roads can be on private land or can be constructed on government land for use by go ...
: Road owned and maintained by a private individual, organization, or company rather than by a government ;
Profile Profile or profiles may refer to: Art, entertainment and media Music * ''Profile'' (Jan Akkerman album), 1973 * ''Profile'' (Githead album), 2005 * ''Profile'' (Pat Donohue album), 2005 * ''Profile'' (Duke Pearson album), 1959 * '' ''Profi ...
: 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 Cycling, also, when on a two-wheeled bicycle, called bicycling or biking, is the use of Bicycle, cycles for transport, recreation, Physical exercise, exercise or sport. People engaged in cycling are referred to as "cyclists", "bicyclists", ...
, generally between 1.5–7 metres of setback, a forward stop bar, which allows cyclists to stop for a
traffic light Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at intersection (road), road intersections, pedestrian crossings, and other locations in order to control flows of traf ...
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
kerb A curb (North American English), or kerb (Commonwealth English except Canada; see spelling differences), is the edge where a raised sidewalk or road median/central reservation meets a street or other roadway. History Although curbs have ...
s 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 A public space is a place that is open and accessible to the general public. Roads (including the pavement), public squares, parks, and beaches are typically considered public space. To a limited extent, government buildings which are open to ...
: Place where anyone has a right to come without being excluded because of economic or social conditions ;
Ranch road In the United States, a farm-to-market road or ranch-to-market road (sometimes farm road or ranch road for short) is a state highway or county road that connects rural or agricultural areas to market towns. These are better quality roads, usually ...
: U.S. road that connects rural and agricultural areas to
market town A market town is a settlement most common in Europe that obtained by custom or royal charter, in the Middle Ages, a market right, which allowed it to host a regular market; this distinguished it from a village or city. In Britain, small rural ...
s ; Road number: Often assigned to identify a stretch of public roads – often dependent on the type of road, with numbers differentiating between
interstates The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate Highway System, is a network of controlled-access highways that forms part of the National Highway System in the United States. T ...
, motorways, arterial thoroughfares, etc. ;
Road-traffic safety Road traffic safety refers to the methods and measures used to prevent road users from being killed or seriously injured. Typical road users include pedestrians, cyclists, Driving, motorists, vehicle passengers, horse riders, and passengers o ...
: Process to reduce the harm (deaths, injuries, and property damage) that result from vehicle crashes on public roads ;
Roadworks Roadworks (called road work or road construction in the United States) 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. In the ...
: 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 Ride quality refers to a vehicle's effectiveness in insulating the occupants from undulations in the road surface (e.g., bumps or corrugations). A vehicle with good ride quality provides a comfort for the driver and passengers. Importance Good r ...
, 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
kerb A curb (North American English), or kerb (Commonwealth English except Canada; see spelling differences), is the edge where a raised sidewalk or road median/central reservation meets a street or other roadway. History Although curbs have ...
s 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 The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder mak ...
(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 h ...
) in the hierarchy ''or'' a road maintained by the state, including nationally numbered highways ;
Traffic Traffic comprises pedestrians, vehicles, ridden or herded animals, trains, and other conveyances that use public ways (roads) for travel and transportation. Traffic laws govern and regulate traffic, while rules of the road include traffic ...
: Pedestrians, ridden or herded animals, vehicles, bicycles, and other conveyances using any road for purposes of travel. ;
Texture (roads) Road surface textures are deviations from a planar and smooth surface, affecting the vehicle/tyre interaction. Pavement texture is divided into: microtexture with wavelengths from 0 mm to , macrotexture with wavelengths from to and megatex ...
: 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 uses physical design and other measures to improve safety for motorists, pedestrians and bicycle-friendly, cyclists. It has become a tool to combat speeding and other unsafe behaviours of drivers in the neighbourhoods. It aims ...
: Set of strategies used by
urban planner An urban planner (also known as town planner) is a professional who practices in the field of town planning, urban planning or city planning. An urban planner may focus on a specific area of practice and have a title such as city planner, town ...
s and
traffic engineers 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. It focuses mainly on research for safe and efficient traffic flow, such as road geo ...
to slow down or reduce motor vehicle traffic, thereby improving safety for pedestrians and
bicyclists Cycling, also, when on a two-wheeled bicycle, called bicycling or biking, is the use of cycles for transport, recreation, exercise or sport. People engaged in cycling are referred to as "cyclists", "bicyclists", or "bikers". Apart from two ...
and improving the environment for residents ;
Traffic island A traffic island is a solid or painted object in a road that channels 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 curbs or other physica ...
: (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 Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at intersection (road), road intersections, pedestrian crossings, and other locations in order to control flows of traf ...
: 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 A zebra crossing (British English) or a marked crosswalk (American English) is a pedestrian crossing marked with white stripes (zebra markings). Normally, pedestrians are afforded precedence over vehicular traffic, although the significance of ...
(UK): A pedestrian crossing marked by black and white stripes on the carriageway


Construction

In
transport engineering Transportation engineering or transport engineering is the application of technology and scientific principles to the planning, functional design, operation and management of facilities for any mode of transportation in order to provide for th ...
, subgrade is the native material underneath a constructed road. Road construction requires the creation of an engineered 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 A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A Pipeline transport, pipeline is not a tunnel, though some recent tunnels have used ...
, and removal of vegetation (this may involve
deforestation Deforestation or forest clearance is the removal of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. The most concentrated d ...
) 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 A biophysical environment is a biotic and abiotic surrounding of an organism or population, and consequently includes the factors that have an influence in their survival, development, and evolution. A biophysical environment can vary in scale f ...
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 In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
and
gradient In vector calculus, the gradient of a scalar-valued differentiable function of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p is the "direction and rate of fastest increase". If the gradi ...
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 A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses, mobility scooters for disabled people), railed vehicles (trains, trams), wa ...
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 Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
and
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
controls are constructed to prevent detrimental effects. Drainage lines are laid with sealed 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 A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams are ...
, creek, river or the sea for drainage discharge. A
borrow pit Digging, also referred to as excavation, is the process of using some implement such as claws, hands, manual tools or heavy equipment, to remove material from a solid surface, usually soil, sand or rock on the surface of Earth. Digging is actu ...
(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 Local government is a generic term for the lowest tiers of public administration within a particular sovereign state. This particular usage of the word government refers specifically to a level of administration that is both geographically-loca ...
may be required to draw water or for working (crushing and screening) of materials for construction needs. The
topsoil Topsoil is the upper layer of soil. It has the highest concentration of organic matter and microorganisms and is where most of the Earth's biological soil activity occurs. Description Topsoil is composed of mineral particles and organic matt ...
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 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 should be free of organics, meet minimum California bearing ratio (CBR) results and have a low
plasticity index The Atterberg limits are a basic measure of the critical water contents of a fine-grained soil: its shrinkage limit, plastic limit, and liquid limit. Depending on its water content, soil may appear in one of four states: solid, semi-solid, plastic ...
. 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 A sieve, fine mesh strainer, or sift, is a device for separating wanted elements from unwanted material or for controlling the particle size distribution of a sample, using a screen such as a woven mesh or net or perforated sheet material. T ...
d) 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 Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wales ...
or broken rock below a specified
particle size Particle size is a notion introduced for comparing dimensions of solid particles ('' flecks''), liquid particles ('' droplets''), or gaseous particles ('' bubbles''). The notion of particle size applies to particles in colloids, in ecology, in ...
and be free of large lumps of
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
. Sand clay fill may also be used. The roadbed must be "proof rolled" after each layer of fill is compacted. If a roller passes over an area without creating visible deformation or spring the section is deemed to comply.
Geosynthetics Geosynthetics are synthetic products used to stabilize terrain. They are generally polymeric products used to solve civil engineering problems. This includes eight main product categories: geotextiles, geogrids, geonets, geomembranes, geosyntheti ...
such as
geotextiles Geotextiles are permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain. Typically made from polypropylene or polyester, geotextile fabrics come in two basic forms: woven (re ...
,
geogrids A geogrid is geosynthetic material used to reinforce soils and similar materials. Soils pull apart under tension. Compared to soil, geogrids are strong in tension. This fact allows them to transfer forces to a larger area of soil than would otherw ...
, and geocells 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 surface is dependent on economic factors and expected usage.
Safety Safety is the state of being "safe", the condition of being protected from harm or other danger. Safety can also refer to risk management, the control of recognized hazards in order to achieve an acceptable level of risk. Meanings There are ...
improvements such as
traffic sign Traffic signs or road signs are signs erected at the side of or above roads to give instructions or provide information to road users. The earliest signs were simple wooden or stone milestones. Later, signs with directional arms were introduce ...
s,
crash barrier Traffic barriers (sometimes called Armco barriers,AK Steel (formerly Armco) genericized trademark also known in North America as guardrails or guard rails and in Britain as crash barriers) keep vehicles within their roadway and prevent them fro ...
s,
raised pavement marker A raised pavement marker is a safety device used on roads. These devices are usually made with plastic, ceramic, thermoplastic paint, glass or occasionally metal, and come in a variety of shapes and colors. Raised reflective markers, such as ...
s and other forms of
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 are commonly placed with road marking machines (also referred to as road marking equipment or pavement marking eq ...
are installed. According to a May 2009 report by the
American Association of State Highway and Transportation Officials The American Association of State Highway and Transportation Officials (AASHTO) is a standards setting body which publishes specifications, test quality control, protocols, and guidelines that are used in highway design and construction through ...
(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 A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but ...
, and
tire wear A tire (American English) or tyre (British English) is a ring-shaped component that surrounds a wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide traction on the surface over which t ...
caused by poor road conditions. When a
single carriageway A single carriageway (British English) or Undivided highway (American English) is a road with one, two or more lanes arranged within a one carriageway with no central reservation to separate opposing flows of traffic. A single-track road has a s ...
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 Single may refer to: Arts, entertainment, and media * Single (music), a song release Songs * "Single" (Natasha Bedingfield song), 2004 * "Single" (New Kids on the Block and Ne-Yo song), 2008 * "Single" (William Wei song), 2016 * "Single", by ...
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 sign Traffic signs or road signs are signs erected at the side of or above roads to give instructions or provide information to road users. The earliest signs were simple wooden or stone milestones. Later, signs with directional arms were introduce ...
s. 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 Cycling, also, when on a two-wheeled bicycle, called bicycling or biking, is the use of cycles for transport, recreation, exercise or sport. People engaged in cycling are referred to as "cyclists", "bicyclists", or "bikers". Apart from two ...
and/or
walking Walking (also known as ambulation) is one of the main gaits of terrestrial locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined by an 'inverted pendulum' gait in which the body vaults o ...
.


Maintenance

Like all structures, roads deteriorate over time. Deterioration is primarily due to environmental effects such as
frost heave Frost heaving (or a frost heave) is an upwards swelling of soil during freezing conditions caused by an increasing presence of ice as it grows towards the surface, upwards from the depth in the soil where freezing temperatures have penetrated in ...
s, 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 The AASHO Road Test was a series of experiments carried out by the American Association of State Highway and Transportation Officials (AASHTO), to determine how traffic contributed to the deterioration of highway pavements. Methodology Of ...
, it was empirically determined that the effective damage done to the road is roughly proportional to the
fourth power In arithmetic and algebra, the fourth power of a number ''n'' is the result of multiplying four instances of ''n'' together. So: :''n''4 = ''n'' × ''n'' × ''n'' × ''n'' Fourth powers are also formed by multiplying a number by its cube. Further ...
of axle weight. A typical
tractor-trailer A semi-trailer truck, also known as a semitruck, (or semi, eighteen-wheeler, big rig, tractor-trailer or, by synecdoche, a semitrailer) is the combination of a tractor unit and one or more semi-trailers to carry freight. A semi-trailer a ...
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 Pavement may refer to: * Pavement (architecture), an outdoor floor or superficial surface covering * Road surface, the durable surfacing of roads and walkways ** Asphalt concrete, a common form of road surface * Sidewalk or pavement, a walkway al ...
are designed for an expected
service life A product's service life is its period of use in service. Several related terms describe more precisely a product's life, from the point of manufacture, storage, and distribution, and eventual use. Service life has been defined as "a product's ...
or
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. It is not always the actual length of tim ...
. 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 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 ...
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 (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...
's
Wacker Drive Wacker Drive is a major multilevel street in Chicago, Illinois, running along the south side of the main branch and the east side of the south branch of the Chicago River in the Loop.Hayner, Don and Tom McNamee, ''Streetwise Chicago'', "Wacker D ...
, 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 The technical meaning of maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure, and supporting utilities in industrial, business, and residential installa ...
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 Profilometers. 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 Cross slope, cross fall or camber is a geometric feature of pavement surfaces: the transverse slope with respect to the horizon. It is a very important safety factor. Cross slope is provided to provide a drainage gradient so that water will run o ...
, asperity, roughness, rutting and
texture Texture may refer to: Science and technology * Surface texture, the texture means smoothness, roughness, or bumpiness of the surface of an object * Texture (roads), road surface characteristics with waves shorter than road roughness * 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 Diamond grinding is a grinding process that can be applied to a variety of surfaces including floors, stones, and engineering ceramics. It takes advantage of the fact that diamond has the highest hardness of any bulk material. See also * Diamond ...
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 A dowel bar retrofit (DBR) is a method of reinforcing cracks in highway pavement by inserting steel dowel bars in slots cut across the cracks. It is a technique which several U.S. states' departments of transportation have successfully used in re ...
, 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 Cardiopulmonary resuscitation (CPR) is an emergency procedure consisting of chest compressions often combined with artificial ventilation in an effort to manually preserve intact brain function until further measures are taken to restore sponta ...
) 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 Polyurethane (; often abbreviated PUR and PU) refers to a class of polymers composed of organic chemistry, organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethan ...
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 Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
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 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 Pozzolans are a broad class of Silicon_dioxide, siliceous and aluminium oxide, aluminous materials which, in themselves, possess little or no cementitious value but which will, in finely divided form and in the presence of water, react chemically ...
-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 Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debris: scattered pieces of waste or remains * Dust: a genera ...
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 Road traffic safety refers to the methods and measures used to prevent road users from being killed or seriously injured. Typical road users include pedestrians, cyclists, motorists, vehicle passengers, horse riders, and passengers of on-ro ...
and reduce the harm (deaths, injuries, and property damage) on the highway system from traffic collisions. On neighborhood roads
traffic calming Traffic calming uses physical design and other measures to improve safety for motorists, pedestrians and bicycle-friendly, cyclists. It has become a tool to combat speeding and other unsafe behaviours of drivers in the neighbourhoods. It aims ...
,
safety barriers A safety barrier is a component which prevents passage into a dangerous area, commonly used to mitigate risk. Safety barriers may be hard barriers physically restricting passage or soft barriers that control circuits based on the presence of forei ...
, 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 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 Speed limits on road traffic, as used in most countries, set the legal maximum speed at which vehicles may travel on a given stretch of road. Speed limits are generally indicated on a traffic sign reflecting the maximum permitted speed - expres ...
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) The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
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 Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere, the ...
. 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 Vehicular automation involves the use of mechatronics, artificial intelligence, and multi-agent systems to assist the operator of a vehicle (car, aircraft, watercraft, or otherwise).Hu, J.; Bhowmick, P.; Lanzon, A.,Group Coordinated Control o ...
such as
self-driving car A self-driving car, also known as an autonomous car, driver-less car, or robotic car (robo-car), is a car that is capable of traveling without human input.Xie, S.; Hu, J.; Bhowmick, P.; Ding, Z.; Arvin, F.,Distributed Motion Planning for S ...
s, 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.
Rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...
water and
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 part ...
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 Trash may refer to: Garbage * Garbage, unwanted or undesired waste material ** Litter, material discarded in inappropriate places ** Municipal solid waste, unwanted or undesired waste material generated in a municipal environment Arts, enter ...
and other pollutants and result in
water pollution Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water ...
. Road runoff is a major source of
nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...
, copper,
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
,
cadmium Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of ...
, lead and
polycyclic aromatic hydrocarbon A polycyclic aromatic hydrocarbon (PAH) is a class of organic compounds that is composed of multiple aromatic rings. The simplest representative is naphthalene, having two aromatic rings and the three-ring compounds anthracene and phenanthrene. ...
s (PAHs), which are created as
combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...
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 Deicing is the process of removing snow, ice or frost from a surface. Anti-icing is the application of chemicals that not only deice but also remain on a surface and continue to delay the reformation of ice for a certain period of time, or prev ...
chemicals and sand can run off into roadsides, contaminate
groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...
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 salt Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g/ ...
s 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 Noise pollution, also known as environmental noise or sound pollution, is the propagation of noise with ranging impacts on the activity of human or animal life, most of them are harmful to a degree. The source of outdoor noise worldwide is main ...
. 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 Engine braking occurs when the retarding forces within an engine are used to slow down a motor vehicle, as opposed to using additional external braking mechanisms such as friction brakes or magnetic brakes. The term is often confused with sever ...
.
Motor vehicle emissions Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline (petrol), diesel fuel, fuel oil, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through an ...
contribute
air pollution Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different types ...
. Concentrations of air pollutants and adverse
respiratory The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...
health effects are greater near the road than at some distance away from the road.
Road dust Dust is made of fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian process), volcanic eruptions, and pollution. Dust in hom ...
kicked up by vehicles may trigger
allergic Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic der ...
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 circle A roundabout is a type of circular intersection (road), 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 N ...
s 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 Transport economics is a branch of economics founded in 1959 by American economist John R. Meyer that deals with the allocation of resources within the transport sector. It has strong links to civil engineering. Transport economics differs from ...
is used to understand both the relationship between the transport system and the wider economy and the complex
network effect In economics, a network effect (also called network externality or demand-side economies of scale) is the phenomenon by which the value or utility a user derives from a good or service depends on the number of users of compatible products. Net ...
s when there are multiple paths and competing modes for both personal and freight (road/rail/air/ferry) and where
induced demand In economics, induced demand – related to latent demand and generated demandSchneider, Benjamin (September 6, 2018"CityLab University: Induced Demand"''CityLab'' – is the phenomenon whereby an increase in supply results in a decline ...
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 The public sector, also called the state sector, is the part of the economy composed of both public services and public enterprises. Public sectors include the public goods and governmental services such as the military, law enforcement, infra ...
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 A general contractor, main contractor or prime contractor is responsible for the day-to-day oversight of a construction site, management of vendors and trades, and the communication of information to all involved parties throughout the course of ...
). or occasionally using road tolls. 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 In economics, goods are items that satisfy human wants and provide utility, for example, to a consumer making a purchase of a satisfying product. A common distinction is made between goods which are transferable, and services, which are not tran ...
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 The Connecticut Turnpike (officially the Governor John Davis Lodge Turnpike) is a controlled-access highway and former toll road in the U.S. state of Connecticut; it is maintained by the Connecticut Department of Transportation (ConnDOT). Span ...
– $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 The Pennsylvania Turnpike (Penna Turnpike or PA Turnpike) is a toll highway operated by the Pennsylvania Turnpike Commission (PTC) in the U.S. state of Pennsylvania. A controlled-access highway, it runs for across the state. The turnpike's we ...
(Delaware Extension) – $1,970,000 per mile * Northern Indiana Toll Road – $1,790,000 per mile *
Garden State Parkway The Garden State Parkway (GSP) is a controlled-access toll road that stretches the north–south length of eastern New Jersey from the state's southernmost tip near Cape May to the New York state line at Montvale. Its name refers to New Jersey ...
– $1,720,000 per mile *
Massachusetts Turnpike The Massachusetts Turnpike (colloquially "Mass Pike" or "the Pike") is a toll highway in the US state of Massachusetts that is maintained by the Massachusetts Department of Transportation (MassDOT). The turnpike begins at the New York state li ...
– $1,600,000 per mile * Thruway, New York to Pennsylvania Line – $1,547,000 per mile *
Ohio Turnpike The Ohio Turnpike, officially the James W. Shocknessy Ohio Turnpike, is a limited-access toll highway in the U.S. state of Ohio, serving as a primary corridor between Chicago and Pittsburgh. The road runs east–west in the northern section of ...
– $1,352,000 per mile *
Pennsylvania Turnpike The Pennsylvania Turnpike (Penna Turnpike or PA Turnpike) is a toll highway operated by the Pennsylvania Turnpike Commission (PTC) in the U.S. state of Pennsylvania. A controlled-access highway, it runs for across the state. The turnpike's we ...
(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 This is a list of countries (or regions) by total road network size, both paved and unpaved. Also included is additional data on the length of each country's or region's controlled-access highway network, also known as motorway, expressway, freewa ...
. 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 The expressway network of China, with the national-level expressway system officially known as the National Trunk Highway System (; abbreviated as NTHS), is an integrated system of national and provincial-level expressways in China.Li, Si-min ...
(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 Darién Gap (, , es, Tapón del Darién , ) is a geographic region between the North and South American continents within Central America, consisting of a large watershed, forest, and mountains in Panama's Darién Province and the norther ...
, the only interruption in the
Pan-American Highway The Pan-American Highway (french: (Auto)route panaméricaine/transaméricaine; pt, Rodovia/Auto-estrada Pan-americana; es, Autopista/Carretera/Ruta Panamericana) is a network of roads stretching across the Americas and measuring about in to ...
. Eurasia and Africa are connected by roads on the
Sinai Peninsula The Sinai Peninsula, or simply Sinai (now usually ) (, , cop, Ⲥⲓⲛⲁ), is a peninsula in Egypt, and the only part of the country located in Asia. It is between the Mediterranean Sea to the north and the Red Sea to the south, and is a l ...
. 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 The Öresund or Øresund Bridge ( da, Øresundsbroen ; sv, Öresundsbron ; hybrid name: ) is a combined railway and motorway bridge across the Øresund strait between Denmark and Sweden. It is the longest in Europe with both roadway and rai ...
, 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 Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
has very few roads and no continent-bridging network, though there are a few
ice road An ice road or ice bridge is a human-made structure that runs on a frozen water surface (a river, a lake or a sea water expanse).Masterson, D. and Løset, S., 2011, ISO 19906: Bearing capacity of ice and ice roads, Proceedings of the 21st Inte ...
s 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 Bahrain ( ; ; ar, البحرين, al-Bahrayn, locally ), officially the Kingdom of Bahrain, ' is an island country in Western Asia. It is situated on the Persian Gulf, and comprises a small archipelago made up of 50 natural islands and an ...
is the only
island country An island country, island state or an island nation is a country whose primary territory consists of one or more islands or parts of islands. Approximately 25% of all independent countries are island countries. Island countries are historically ...
to be connected to a continental network by road (the
King Fahd Causeway The King Fahd Causeway ( ar, جسر الملك فهد, Jisr al-Malik Fahd) is a 25 km (15.5 mi) long series of bridges and causeways connecting Khobar, Saudi Arabia and Al Jasra, Bahrain. Its five bridges rest on 536 concrete pylons, with ...
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 The Overseas Highway is a highway carrying U.S. Route 1 (US 1) through the Florida Keys to Key West. Large parts of it were built on the former right-of-way of the Overseas Railroad, the Key West Extension of the Florida East Coast Rail ...
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 A developing country is a sovereign state with a lesser developed industrial base and a lower Human Development Index (HDI) relative to other countries. However, this definition is not universally agreed upon. There is also no clear agreem ...
, 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 Four-wheel drive, also called 4×4 ("four by four") or 4WD, refers to a two-axled vehicle drivetrain capable of providing torque to all of its wheels simultaneously. It may be full-time or on-demand, and is typically linked via a transfer case ...
vehicles, those with snow chains or
snow tire Snow tires, also known as winter tires, are tires designed for use on snow and ice. Snow tires have a tread design with larger gaps than those on conventional tires, increasing traction on snow and ice. Such tires that have passed a specific wi ...
s, 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 Amphibious warfare is a type of Offensive (military), offensive military operation that today uses naval ships to project ground and air power onto a hostile or potentially hostile shore at a designated landing beach. Through history the opera ...
. 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 Roll-on/roll-off (RORO or ro-ro) ships are cargo ships designed to carry wheeled cargo, such as cars, motorcycles, trucks, semi-trailer trucks, buses, trailers, and railroad cars, that are driven on and off the ship on their own wheels or using ...
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 Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It is ...
is connected to the European road network by
Eurotunnel Shuttle Eurotunnel Le Shuttle (sometimes shortened to Le Shuttle or The Shuttle) is a railway shuttle service between Coquelles (near Calais) in Pas-de-Calais, France and Cheriton, Kent, Cheriton (near Folkestone) in Kent, United Kingdom. It conveys ro ...
– an example of a
car shuttle train A car shuttle train, or (sometimes) car-carrying train, is a shuttle train used to transport accompanied cars ( automobiles), and usually also other types of road vehicles, for a relatively short distance. Car shuttle trains usually operate on ...
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 A snowmobile, also known as a Ski-Doo, snowmachine, sled, motor sled, motor sledge, skimobile, or snow scooter, is a motorized vehicle designed for winter travel and recreation on snow. It is designed to be operated on snow and ice and does not ...
or
dogsled A dog sled or dog sleigh is a sled pulled by one or more sled dogs used to travel over ice and through snow. Numerous types of sleds are used, depending on their function. They can be used for dog sled racing. Traditionally in Greenland and the ...
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 The James W. Dalton Highway, usually referred to as the Dalton Highway (and signed as Alaska Route 11), is a road in Alaska. It begins at the Elliott Highway, north of Fairbanks, and ends at Deadhorse (an unincorporated community within the ...
to the North Slope of Alaska, the R21 highway to
Murmansk Murmansk (Russian: ''Мурманск'' lit. "Norwegian coast"; Finnish: ''Murmansk'', sometimes ''Muurmanski'', previously ''Muurmanni''; Norwegian: ''Norskekysten;'' Northern Sámi: ''Murmánska;'' Kildin Sámi: ''Мурман ланнҍ'') i ...
in Russia, and many roads in Scandinavia (though due to
fjord In physical geography, a fjord or fiord () is a long, narrow inlet with steep sides or cliffs, created by a glacier. Fjords exist on the coasts of Alaska, Antarctica, British Columbia, Chile, Denmark, Germany, Greenland, the Faroe Islands, Ice ...
s water transport is sometimes faster). Large areas of Alaska, Canada, Greenland, and
Siberia Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of ...
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 The Annapurna Circuit is a trek within the mountain ranges of central Nepal. The total length of the route varies between 160–230 km (100-145 mi), depending on where motor transportation is used and where the trek is ended. This trek c ...
, and a road was completed in 2013 to
Mêdog County Mêdog, or Metok, or Motuo County (; ), also known as Pemako ( meaning "Lotus Array", ), is a county as well as a traditional region of the prefecture-level city of Nyingchi in the Tibet Autonomous Region of the China, People's Republic of Chin ...
. Additional
intercontinental and transoceanic fixed links A fixed link or fixed crossing is a persistent, unbroken road or rail connection across water that uses some combination of bridges, tunnels, and causeways and does not involve intermittent connections such as drawbridges or ferries. A bridge–tu ...
have been proposed, including a
Bering Strait crossing A Bering Strait crossing is a hypothetical bridge or tunnel that would span the relatively narrow and shallow Bering Strait between the Chukotka Peninsula in Russia and the Seward Peninsula in the U.S. state of Alaska. The crossing would prov ...
that would connect Eurasia-Africa and North America, a
Malacca Strait Bridge The Central Spine Road 2 or Malacca Strait Bridge (Indonesian: ''Jembatan Selat Malaka'', Malaysian: ''Jambatan Selat Melaka'' or ''JSM'' and ''Jembatan Selmal'') is a proposed bridge that would connect Teluk Gong, near Masjid Tanah, Malacca ...
to the largest island of
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
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