View source for Road

{{Short description|Land route for travel by vehicles}}
{{other uses}}
[[File:Erlangen Bundesautobahn 73 Auffahrt Luftbild-20230422-RM-165734.jpg|thumb|upright=1.5|[[Bundesautobahn 73]] and its [[slip road]] leading to [[Erlangen]]]]
{{Public Infrastructure}}

A '''road''' is a [[thoroughfare]] for the conveyance of [[traffic]] that mostly has an [[road surface|improved surface]] for use by vehicles (motorized and non-motorized) and pedestrians. Unlike [[street]]s, whose primary function is to serve as public spaces, the main function of roads is transportation.

There are [[road hierarchy|many types of roads]], including [[parkway]]s, [[avenue (landscape)|avenue]]s, [[controlled-access highway]]s (freeways, motorways, and expressways), [[tollway]]s, [[interstate]]s, [[highway]]s, [[thoroughfare]]s, and local roads.

The primary features of roads include [[lane]]s, [[sidewalk]]s (pavement), [[roadway]]s (carriageways), [[median strip|medians]], [[shoulder (road)|shoulders]], [[road verge|verges]], [[bike path]]s (cycle paths), and [[shared-use path]]s.

==Definitions==
Historically many roads were simply recognizable routes without any formal construction or some maintenance.<ref name="Ways_of_the_World "/>

The [[Organisation for Economic Co-operation and Development|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".<ref>
{{cite web |url=http://stats.oecd.org/glossary/detail.asp?ID=4005 |publisher= OECD |title= Glossary of Statistical Terms |date= 2004-02-26 |access-date= 2007-07-17}}</ref>

The [[Eurostat]], [[International Transport Forum|ITF]] and [[UNECE]] ''Glossary for Transport Statistics Illustrated'' defines a road as a "Line of communication (traveled way) open to public traffic, primarily for the use of road motor vehicles, using a stabilized base other than rails or air strips. [...] Included are paved roads and other roads with a stabilized base, e.g. gravel roads. Roads also cover streets, bridges, tunnels, supporting structures, junctions, crossings and interchanges. Toll roads are also included. Excluded are dedicated cycle lanes."<ref name="unece.org">{{cite web|url=http://www.unece.org/fileadmin/DAM/trans/main/wp6/pdfdocs/glossen4.pdf|title=Illustrated Glossary for Transport Statistics|publisher=International Transport Forum|access-date=2019-09-27}}</ref>

The 1968 [[Vienna Convention on Road Traffic]] defines a road as the entire surface of any way or street open to public traffic.<ref>{{cite web|url=http://www.unece.org/fileadmin/DAM/trans/conventn/crt1968e.pdf|title=Road Traffic Convention 1968|website=unece.org|access-date=2019-09-27}}</ref>

In urban areas roads may diverge through a city or village and be named as streets, serving a dual function as urban space [[easement]] and route.<ref name="difference_between_road_and_street">{{cite web |title= What is the difference between a road and a street? |work= Word FAQ |publisher= Dictionary.com (Lexico Publishing Group, LLC) |year= 2007 |url=http://dictionary.reference.com/help/faq/language/d01.html |access-date= 2007-03-24 }}</ref> Modern roads are normally smoothed, paved, or otherwise prepared to allow easy [[travel]].<ref name="RoadInfrastructureStrategicFrameworkforSouthAfrica">{{cite web |title=Road Infrastructure Strategic Framework for South Africa; A Discussion Document |publisher=National Department of Transport (South Africa) |url=http://www.transport.gov.za/library/docs/rifsa/infor.html |access-date=2007-03-24 |url-status=dead |archive-url=https://web.archive.org/web/20070927063243/http://www.transport.gov.za/library/docs/rifsa/infor.html |archive-date=2007-09-27 }}</ref>

===Australia===
{{See also|Highways in 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.'<ref>{{Cite web|url=http://www.legislation.gov.au/Details/F2016C00716/Html/Text|title=National Transport Commission (Road Transport Legislation - Australian Road Rules) Regulations 2006|last=Infrastructure|website=legislation.gov.au|language=en|access-date=2019-12-16}}</ref>

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<ref>{{Cite web|url=http://www.legislation.govt.nz/act/public/1998/0110/latest/DLM433613.html|title=Land Transport Act 1998 No 110 (as at 29 October 2019), Public Act Contents – New Zealand Legislation|website=legislation.govt.nz|access-date=2019-12-16}}</ref> where the statutory definition includes areas the public has access to, by right or not.<ref>{{Cite web|url=https://www.nzta.govt.nz/resources/what-is-a-road/what-is-a-road.html|title=What Is a road? {{!}} NZ Transport Agency|website=nzta.govt.nz|access-date=2019-12-16}}</ref> Beaches, publicly accessible car parks and yards (even if privately owned), river beds, road shoulders (verges), wharves and bridges are included.<ref>{{Cite web|url=http://www.drivingtests.co.nz/roadcode-questions/car/core/whats-the-legal-definition-of-a-road/|title=What is the legal definition of a road?|website=drivingtests.co.nz|language=en|access-date=2019-12-16}}</ref> However, the definition of a road for insurance purposes may be restricted to reduce risk.

===United Kingdom===
In the United Kingdom ''[[The Highway Code]]'' details rules for "road users", but there is some ambiguity between the terms ''highway'' and ''road''.<ref>{{Cite web|url=https://www.gov.uk/guidance/the-highway-code/annex-4-the-road-user-and-the-law|title=Annex 4. The road user and the law - The Highway Code - Guidance - GOV.UK|website=www.gov.uk}}</ref> For the purposes of the [[English law]], [[Highways Act 1980]], which covers [[England and Wales]] but not [[Scotland]] or [[Northern Ireland]], road is "any length of highway or of any other road to which the public has access, and includes bridges over which a road passes".<ref>{{cite web|url=http://www.legislation.gov.uk/ukpga/1984/27/section/142|title=Road Traffic Regulation Act 1984 – 142 General interpretation of Act |work=Legislation|quote="road" – (a) in England and Wales, means any length of highway or of any other road to which the public has access, and includes bridges over which a road passes, and (b) in Scotland, has the same meaning as in the Roads (Scotland) Act 1984}}</ref> This includes footpaths, bridleways and cycle tracks, and also road and driveways on private land and many car parks.<ref name=Direct>{{cite web|url=http://www.direct.gov.uk/en/TravelAndTransport/Highwaycode/DG_069869|title=The road user and the law|quote=Most of the provisions apply on all roads throughout Great Britain, although there are some exceptions.}}</ref> [[Vehicle Excise Duty]], a [[Road tax|road use tax]], is payable on some vehicles used on the public road.<ref name=Direct/>

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.<ref>Reference listed says 1984, This description is used in several rules going back to at least 1975, The law of real property; Stevens, 1975; Authors – Robert Megarry, Sir Robert Edgar Megarry, Sir William Wade</ref><ref>{{cite web|url=http://www.hrothgar.co.uk/WebCases/hol/reports/07/44.htm|title=Judgment – Director of Public Prosecutions v. Jones and Another (On Appeal from a Divisional Court of the Queen's Bench Division)|quote=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. There may be a highway over a footpath, while a well made road may be subject only to an easement of way, or may exist only for the landowner's benefit and be subject to no easement at all|url-status=dead|archive-url=https://web.archive.org/web/20100403093123/http://www.hrothgar.co.uk/WebCases/hol/reports/07/44.htm|archive-date=2010-04-03}}</ref> Another legal view is that while a highway historically included [[footpath]]s, [[bridleway]]s, driftways, etc., it can now be used to mean those ways that allow the movement of [[motor vehicles]], and the term ''[[Right-of-way (transportation)|rights of way]]'' can be used to cover the wider usage.<ref>{{cite web|url=http://www.4-5.co.uk/practiceareas/index.cfm?id=486|title=Local government law – Highway law |quote=Historically, a highway comprehended any path in which members of the public had the right to pass and re-pass without let or hindrance. The term embraced footpaths, bridleways, driftways and so forth. The advent of the motor vehicle and its peculiar requirements has seen increasing distinctions between paths over which walkers and riders have a right of way and those ways that are predominantly used by motor vehicles. The former may be usefully termed "rights of way" (and are the subject of a separate entry in this web) and the latter may be termed "highways."}}</ref>

===United States===
In the United States, laws distinguish between ''public roads'', which are open to public use,<ref>{{cite journal |last1=Leonard |first1=M Brent. |title=The Public Nature of Indian Reservation Roads |journal=American Indian Law Journal |date=April 2017 |issue=1 |page=40 |url=https://digitalcommons.law.seattleu.edu/cgi/viewcontent.cgi?article=1002&context=ailj |access-date=8 November 2021}}</ref> and ''private roads'', which are privately controlled.<ref>{{cite book |last1=Levinson |first1=David |title=Street smart : competition, entrepreneurship, and the future of roads |date=2006 |publisher=Transaction Publishers |location=New Brunswick, N.J. |isbn=9781315130330 |page=80}}</ref>

==History==
{{Main|History of road transport}}
{{Further|Gravel road|Trail}}
[[File:Greek street - III century BC - Porta Rosa - Velia - Italy.JPG|thumb| The Porta Rosa, a Greek street dating from the 3rd to 4th century BC in [[Velia]], with a [[road surface|paved]] surface and [[Street gutter|gutters]]]]
[[File:PompeiiStreet.jpg|thumb|upright| A paved Roman road in [[Pompeii]]]]
The assertion that the first pathways were the [[trail]]s made by animals has not been universally accepted; in many cases animals do not follow constant paths.<ref name="Ways_of_the_World">{{cite book | last= Lay | first= Maxwell G | title= Ways of the World: A History of the World's Roads and of the Vehicles that Used Them | publisher= Rutgers University Press | year= 1992 |url=https://archive.org/details/waysofworldhisto00laym | url-access= registration | quote= Ways of the world Rutgers University Press, New Brunswick. | isbn= 978-0-8135-2691-1 }}</ref> Some believe that some roads originated from following animal trails.<ref>{{cite journal |first1= D. |last1= Helbing |first2= P. |last2= Molnär |first3= I.J. | last3= Farkas |first4= K. |last4= Bolay | title= Environment and Planning B: Planning and Design 2001, volume 28 (Self-organizing pedestrian movement) |journal= Environment and Planning B: Planning and Design |volume= 28 |issue= 3 | page= 376 |url=http://pedsim.elte.hu/pdf/envplanb.pdf | doi= 10.1068/b2697 |year= 2001 |s2cid= 16276539 }}</ref><ref name="wheathampstead">{{cite web | title= Marshalls Heath Nature Reserve | work= History | publisher= wheathampstead.net | date= 24 February 2003 |url=http://www.wheathampstead.net/mh/history.htm | access-date= 2007-04-28 }}</ref> The [[Icknield Way]] may exemplify this type of road origination, where human and animal both selected the same natural line.<ref name="Icknield">{{cite web | title= The Icknield Way Path | publisher= Icknield Way Association | year= 2004 |url=http://www.icknieldwaypath.co.uk/ | access-date= 2007-04-29 }}</ref> By about 10,000 BC human travelers used rough roads/pathways.<ref name="Ways_of_the_World"/>
* The world's oldest known paved road was constructed in Egypt some time between 2600 and 2200 BC.<ref>
{{cite news |url=https://www.nytimes.com/1994/05/08/world/world-s-oldest-paved-road-found-in-egypt.html | author= John Noble Wildord | title= World's Oldest Paved Road Found in Egypt |newspaper= [[The New York Times]] | date= 1994-05-08 | access-date= 2012-02-11}}
</ref>
* [[Cobblestone|Stone]]-paved streets appear in the city of [[Ur]] in the Middle East dating back to 4000 BC.<ref name="Ways_of_the_World"/>
* [[Corduroy road]]s (log roads) are found dating to 4000 BC in [[Glastonbury, England|Glastonbury]], England.<ref name="Ways_of_the_World"/>
* The [[Sweet Track]], a [[timber trackway|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]] – enabled very precise dating). It was claimed to be the oldest road in the world<ref name="Current_Archaeology_172">{{cite web | title= The Somerset Levels (the oldest timber trackway discovered in Northern Europe) | work= Current Archaeology 172 | publisher= Current Archaeology |date= February 2001 |url=http://www.archaeology.co.uk/ca/issues/ca172/ca172.htm | access-date= 2007-03-25 | archive-url=https://web.archive.org/web/20070311003620/http://www.archaeology.co.uk/ca/issues/ca172/ca172.htm <!-- Bot retrieved archive --> | archive-date= 2007-03-11}}</ref><ref name="Highways:_The_Location"/> until the 2009 discovery of a 6,000-year-old trackway in [[Plumstead]], London.<ref>{{cite web |url=http://archaeology.about.com/b/2009/08/15/oldest-trackway-found-in-plumstea.htm |title= Oldest Trackway found in Plumstead |publisher= Archaeology.about.com |date= 2009-08-15 |access-date= 2013-08-14 |archive-date= 2013-05-21 |archive-url=https://web.archive.org/web/20130521135844/http://archaeology.about.com/b/2009/08/15/oldest-trackway-found-in-plumstea.htm |url-status= dead }}</ref><ref>{{cite web|url=http://www.eurekalert.org/pub_releases/2009-08/ucl-let081209.php |title= London's earliest timber structure found during Belmarsh prison dig |publisher= Eurekalert.org |date= 2009-08-12 |access-date= 2013-08-14}}</ref>
* Brick-paved streets appeared in India as early as 3000 BC.<ref name="Ways_of_the_World"/>
* {{circa}} 1995 BC: an early subdividing of roadways evidenced with [[sidewalk]]s built in Anatolia.<ref>
{{cite book
 |url=https://books.google.com/books?id=yTqARXDtXrgC
 |title= Sidewalks: Conflict and Negotiation Over Public Space
 |author= Anastasia Loukaitou-Sideris, Renia Ehrenfeucht
 |year= 2009|publisher= MIT Press|page= 15
 | access-date = 18 November 2018
 | quote = The first sidewalks appeared around 2000 to 1990 B.C. [...] in central Anatolia (modern Turkey) [...].
|isbn= 978-0-262-12307-5
 }}
</ref>
* In 500 BC, [[Darius I the Great]] started an extensive road system for the [[Achaemenid Empire]] (Persia), including the [[Royal Road]], which was one of the finest highways of its time,<ref name="RoyalRoad">{{cite web | last= Lendering | first= Jona | title= Royal Road | work= History of Iran | publisher= Iran Chamber of Society |url=http://www.iranchamber.com/history/achaemenids/royal_road.php | access-date= 2007-04-09 }}</ref> connecting [[Sardis]] (the westernmost major city of the empire) to [[Susa]]. The road remained in use after Roman times. These road systems reached as far east as [[Bactria]] and [[India]].<ref>{{cite book | first= John | last= Boederman |title= The Cambridge Ancient History|url=https://books.google.com/books?id=nNDpPqeDjo0C&pg=PA178|year= 1997|publisher= Cambridge University Press|isbn= 978-0-521-22804-6|page= 178}}</ref>
* In ancient times, transport by river was far easier and faster than transport by road,<ref name="Highways:_The_Location"/> especially considering the cost of road construction and the difference in carrying capacity between [[cart]]s and river [[barge]]s. A hybrid of road transport and ship transport beginning in about 1740 is the [[horse-drawn boat]] in which the horse follows a cleared path along the river bank.<ref name="horseboating">{{cite web | title= Horseboating | publisher= The Horseboating Society |url=http://www.horseboating.org.uk/ | access-date= 2007-04-09 | archive-url=https://web.archive.org/web/20180429105356/http://www.horseboating.org.uk/ | archive-date= 2018-04-29 | url-status= dead }}</ref><ref name="HorseDrawnBoats">{{cite web | title= Horses and Canals 1760–1960 The people & the horses | work= Horse Drawn Boats | publisher= Canal Junction Ltd |url=http://www.canaljunction.com/craft/horsedrawn1.htm | access-date= 2007-04-09 }}</ref>
* From about 312 BC, the [[Roman Empire]] built straight<ref name="Discovering_Roman_Technology"/> strong stone [[Roman road]]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 [[Ancient Rome|Rome]] and covering 78,000 kilometers or 52,964 [[Roman mile]]s of paved roads.<ref name="Highways:_The_Location">{{cite book |last= O'Flaherty |first= Coleman A. |title= Highways: The Location, Design, Construction & Maintenance of Road Pavements |publisher= Elsevier |year= 2002 |url=https://books.google.com/books?id=Ren4sWQ3jKkC&q=ancient+Egyptians+stone+paved+road++Great+Pyramid+in+about+3000+BC&pg=PA1 |isbn= 978-0-7506-5090-8 }}</ref>
* In the 8th century AD, many roads were built throughout the [[Caliphate|Arab Empire]]. The most sophisticated roads were those in [[Baghdad]], which were paved with [[tar]]. Tar was derived from petroleum, accessed from [[oil field]]s in the region, through the chemical process of [[destructive distillation]].<ref name=Ajram>{{cite book|author= Kasem Ajram|title=The Miracle of Islam Science|edition=2nd|publisher=Knowledge House Publishers|year=1992|isbn=978-0-911119-43-5}}</ref>
* The [[Highways Act 1555]] in Britain transferred responsibility for maintaining roads from government to local parishes.<ref name="Highways:_The_Location"/> This resulted in a poor and variable state of roads. To remedy this, the first of the [[turnpike trust]]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 {{convert|36,800|km|mi|abbr=on}} of engineered roads.<ref name="Highways:_The_Location"/> The [[Rebecca Riots]] in Carmarthenshire and [[Rhayader]] from 1839 to 1844 contributed to a [[Royal Commission]] that led to the demise of the system in 1844,<ref name="Victorian_Powys">
{{cite web
 |title= The Rebecca Riots
 |work= Rebecca and her daughters come to Rhayader
 |publisher= Victorian Powys for Schools |date= March 2002
 |url=http://history.powys.org.uk/school1/rhayader/rebcmenu.shtml
 |access-date= 2007-04-28
}}
</ref> which coincided with the [[History of rail transport in Great Britain to 1830|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]] and [[Barcola]], [[Italy]], in 1928 was very much focused on creating jobs.<ref>Theodor Christomannos: Die Dolomitenstraße Bozen – Cortina – Toblach. Chiari: Ed. Nordpress 1998, {{ISBN|88-85382-37-1}}</ref><ref>Roberto Covaz e Annalisa Turel, La Costiera triestina - storia e misteri di una strada, Edizioni Mgs Press, Trieste, 2006, {{ISBN|88-89219-23-8}}.</ref>
* The ''Autostrada dei Laghi''  ("Lakes Motorway") in Italy, the first [[controlled-access highway]] built in the world,<ref name=independent>{{Cite news |first=Thea |last=Lenarduzzi |url=http://www.independent.co.uk/travel/europe/the-worlds-first-motorway-piero-puricellis-masterpiece-is-the-focus-of-an-unlikely-pilgrimage-a6840816.html|title=The motorway that built Italy: Piero Puricelli's masterpiece|date=30 January 2016|newspaper=[[The Independent]]|access-date=12 May 2022}}</ref><ref name="motorwebmuseum">{{cite web|url=https://www.motorwebmuseum.it/en/places/varese/the-milano-laghi-by-piero-puricelli-the-first-motorway-in-the-world/|title=The "Milano-Laghi" by Piero Puricelli, the first motorway in the world|access-date=10 May 2022}}</ref> connecting [[Milan]] to [[Lake Como]] and [[Lake Maggiore]], and now parts of the [[Autostrada A8 (Italy)|A8]] and [[Autostrada A9 (Italy)|A9]] motorways, was devised by [[Piero Puricelli]] and was inaugurated in 1924.<ref name="motorwebmuseum"/> This motorway, called ''[[autostrada]]'', contained only one lane in each direction and no interchanges.

==Construction==
{{See also|Roadworks|Macadam|Track bed}}
[[File:MortarlessPavement.jpg|thumb|Layers in the construction of a mortarless pavement: A) [[Subgrade]] B) [[Subbase (pavement)|Subbase]] C) [[Base course]] D) [[Paver base]] E) [[Paver (flooring)|Pavers]] F) Fine-grained [[sand]]]]

In [[transport engineering]], '''subgrade''' is the native material underneath a constructed road.[[File:Motorway construction in Ireland.JPG|thumb|[[Subbase (pavement)|Sub-base layer]] composed of cement-based material being applied during construction of the [[M8 motorway (Ireland)|M8 motorway]] in [[Motorways in the Republic of Ireland|Ireland]]]]
[[File:MyanmarRoadConstruction2.jpg|thumb|Road construction in [[Myanmar]]]]'''Road construction''' requires the creation of an [[civil engineering|engineered]] continuous right-of-way or '''roadbed''', overcoming geographic obstacles and having [[grade (slope)|grades]] low enough to permit vehicle or [[walking|foot travel]],<ref name="Kitsap_County_Road_Standards">{{cite web |title=Kitsap County Road Standards 2006 |publisher=Kitsap County, Washington |year=2006 |url=http://www.kitsapgov.com/PW/pdf/Revised%20Road%20Standards.doc |format=Doc |access-date=2007-04-20 |url-status=dead |archive-url=https://web.archive.org/web/20060709203052/http://www.kitsapgov.com/pw/pdf/Revised%20Road%20Standards.doc |archive-date=July 9, 2006 }}</ref>{{rp|15}} and may be required to meet standards set by law<ref name="MRSC_road_standards">{{cite web |title= Washington State County Road Standards |work= Chapter 35.78 RCW requires cities and counties to adopt uniform definitions and design standards for municipal streets and roads |publisher= Municipal Research & Services Center of Washington |year= 2005 |url=http://www.mrsc.org/subjects/Transpo/stand/CoRdStand.aspx |access-date= 2007-04-20 |url-status=dead |archive-url=https://web.archive.org/web/20070927185007/http://www.mrsc.org/subjects/Transpo/stand/CoRdStand.aspx |archive-date= 2007-09-27 }}</ref> or official guidelines.<ref name="thelastfrontier">{{cite web|last=Shire of Wyndham East Kimberly |title=Guidelines for rural road design and construction technical specifications |publisher=Western Australia (The Last Frontier) |date=October 2006 |url=http://www.thelastfrontier.com.au/Publications/06K027005-061019-Rural%20Road%20Technical%20Specification%20complete%20(3).pdf |access-date=2007-04-24 |archive-url=https://web.archive.org/web/20070710022035/http://www.thelastfrontier.com.au/Publications/06K027005-061019-Rural%20Road%20Technical%20Specification%20complete%20%283%29.pdf |archive-date=2007-07-10 |url-status=dead }}</ref> The process is often begun with the removal of earth and rock by digging or blasting, construction of [[Embankment (transportation)|embankments]], bridges and [[tunnels]], and removal of vegetation (this may involve [[deforestation]]) and followed by the laying of pavement material. A variety of [[heavy equipment|road building equipment]] is employed in road building.<ref name="Caterpillar">{{cite web |title= Road Building Equipment |work= Constructing roads into forestry work areas |publisher= Caterpillar |year= 2007 |url=http://www.cat.com/cda/layout?m=62323&x=7 |access-date= 2007-04-20 }}</ref><ref name="Volvo">{{cite web|title=Volvo Construction Equipment (Europe) |work=Building the cities, towns, streets, highways and bridges in your neighborhood and in communities around the globe |publisher=Volvo |year=2007 |url=http://www.volvo.com/constructionequipment/europe/en-gb/work+solutions/government/introduction.htm |access-date=2007-04-20 |archive-url=https://web.archive.org/web/20061027082405/http://www.volvo.com/constructionequipment/europe/en-gb/work%2Bsolutions/government/introduction.htm |archive-date=2006-10-27 |url-status=dead }}</ref>

After design, [[Approval rating|approval]], [[planning]], legal, and [[Environmental policy|environmental]] considerations have been addressed alignment of the road is set out by a [[Surveying|surveyor]].<ref name="Discovering_Roman_Technology">{{cite web |last= Hart-Davis |first= Adam |title= Roads and surveying |work= Discovering Roman Technology |publisher= BBC.CO.UK |date= 2001-06-01 |url=http://www.bbc.co.uk/history/ancient/romans/tech_02.shtml |access-date= 2007-04-22 }}</ref> The [[Radius of curvature (mathematics)|radii]] and [[Slope|gradient]] are designed and staked out to best suit the natural ground levels and minimize the amount of cut and fill.<ref name="thelastfrontier"/>{{rp|34}} Great care is taken to preserve reference [[Benchmark (surveying)|Benchmarks]]<ref name="thelastfrontier"/>{{rp|59}}

Roads are designed and built for primary use by [[vehicular]] and pedestrian traffic. [[Storm drain]]age and environmental considerations are a major concern. [[Erosion]] and [[sediment]] controls are constructed to prevent detrimental effects. Drainage lines are laid with [[Seal (mechanical)|sealed]] joints in the road easement with runoff [[coefficient]]s and characteristics adequate for the [[Zoning|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]], [[stream|creek]], river or the sea for drainage discharge.<ref name="thelastfrontier"/>{{rp|38–40}}

A [[borrow pit]] (source for obtaining fill, gravel, and rock) and a water source should be located near or in reasonable distance to the road construction site. Approval from [[local authorities]] may be required to [[Water well|draw water]] or for working (crushing and screening) of materials for construction needs. The [[topsoil]] and vegetation is removed from the borrow pit and stockpiled for subsequent [[Land rehabilitation|rehabilitation]] of the extraction area. Side slopes in the excavation area not steeper than one vertical to two horizontal for safety reasons.<ref name="thelastfrontier"/>{{rp|53–56 }}
<!-- Traffic considerations for work on existing roads are discussed beginning on p. 62 of the "thelastfrontier" reference. -->

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.<ref name="thelastfrontier"/>{{rp|66–67 }}

Processes during earthwork include excavation, removal of material to spoil, filling, compacting, construction and trimming. If rock or other unsuitable material is discovered it is removed, moisture content is managed and replaced with standard fill compacted to meet the design requirements (generally 90–95% relative compaction). [[Rock blasting|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.<ref name="thelastfrontier"/>{{rp|68–69}}

General [[Fill dirt|fill material]] should be free of [[organic compound|organics]], meet minimum [[California bearing ratio]] (CBR) results and have a low [[Atterberg limits#Plasticity index|plasticity index]]. The lower fill generally comprises sand or a sand-rich mixture with fine gravel, which acts as an inhibitor to the growth of plants or other vegetable matter. The compacted fill also serves as lower-stratum drainage. Select second fill ([[sieve]]d) should be composed of [[gravel]], decomposed [[Rock (geology)|rock]] or [[crushed rock|broken rock]] below a specified [[particle size]] and be free of large lumps of [[clay]]. [[Loam|Sand clay]] fill may also be used. The roadbed must be "proof rolled" after each layer of fill is compacted. If a [[Road roller|roller]] passes over an area without creating visible deformation or spring the section is deemed to comply.<ref name="thelastfrontier"/>{{rp|70–72}}

[[Geosynthetics]] such as [[geotextiles]], [[geogrids]], and [[Cellular confinement|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.<ref name=Mainland>[https://www.mainlandaggregates.co.uk/gravel-driveway-construction-guide Step by Step Guide: How to Lay a Gravel Driveway | Mainland Ltd] Gravel Driveway Construction''] at www.mainlandaggregates.co.uk. Retrieved 25 Jan 2015</ref> Geosynthetics perform four main functions in roads: separation, reinforcement, filtration, and drainage; which increase the pavement performance, reduce construction costs and decrease maintenance.<ref>Koerner, R.M. (2012) Designing with geosynthetics, 6th Edition, Xlibris Corporation, US{{self-published source|date=December 2017}}</ref>{{Self-published inline|certain=yes|date=December 2017}}

The completed roadway is finished by paving or left with a gravel or other [[Dirt road|natural]] surface. The [[Types of road|type of road]] surface is dependent on economic factors and expected usage. [[Road-traffic safety|Safety]] improvements such as [[traffic sign]]s, [[crash barrier]]s, [[raised pavement marker]]s and other forms of [[road surface marking]] are installed.

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

When a [[single carriageway]] road is converted into dual carriageway by building a second separate carriageway alongside the first, it is usually referred to as ''duplication'',<ref>[http://www.neotrucks.com/pdf/glossary_abb_refer.pdf Glossary: Princes Highway, Traralgon Bypass – Planning Assessment Report] {{webarchive|url=https://www.webcitation.org/6GHx1Vq3c?url=http://www.neotrucks.com/pdf/glossary_abb_refer.pdf |date=2013-05-01 }} at The State of [[Victoria (Australia)|Victoria]]</ref> ''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 (rail)|single track]] to [[double track]], the new carriageway is not always constructed directly alongside the existing carriageway.

==Reallocation==
{{See also|Modal shift|Car-free movement}}
Roads that are intended for use by a particular mode of transport can be reallocated for another mode of transport,<ref>{{Cite web|url=https://www.wiltshire.gov.uk/highways-new-active-travel-schemes|title=New active travel schemes - Wiltshire Council|website=www.wiltshire.gov.uk}}</ref> i.e. by using [[traffic sign]]s. For instance, in the ongoing road space reallocation effort, some roads (particularly in city centers) which are intended for use by [[car]]s are increasingly being repurposed for [[cycling]] and/or [[walking]].<ref>{{cite web|url=https://ec.europa.eu/environment/pubs/pdf/streets_people.pdf| title = Reclaiming city streets for people}}</ref><ref>{{Cite web|url=https://www.irishtimes.com/news/world/europe/milan-to-reallocate-streets-to-pedestrians-and-cyclists-in-bid-to-reduce-air-pollution-1.4234088?mode=amp|title=Milan to reallocate streets to pedestrians and cyclists in bid to reduce air pollution|website=www.irishtimes.com}}</ref><ref>{{Cite web|url=http://www.theguardian.com/world/2020/apr/11/world-cities-turn-their-streets-over-to-walkers-and-cyclists|title=World cities turn their streets over to walkers and cyclists|date=April 11, 2020|website=the Guardian}}</ref>

==Maintenance==
{{See also|Roadworks|Road surface#Surface deterioration}}
[[File:Baustelle.svg|thumb|upright|"Road works ahead" sign, typically used in Europe]]
Like all structures, roads deteriorate over time. Deterioration is primarily due to environmental effects such as [[frost heave]]s, thermal cracking and oxidation often contribute, however accumulated damage from vehicles also contributes.<ref name="frost">{{cite web |author1= S.Kameyama |author2=M. Kato |author3=A. Kawamura |author4=K. Himeno |author5=A. Kasahara |work= ISAP 9th Conference Titles & Abstracts| id=09044 |title= Effects of Frost Heave on the Longitudinal Profile of Asphalt Pavements in Cold Regions |publisher= International Society for Asphalt Pavements |date= August 2002 |url=http://www.asphalt.org/Pubs/9th_conf_abst.html |access-date= 2007-05-13 |url-status=dead |archive-url=https://web.archive.org/web/20070813141736/http://www.asphalt.org/Pubs/9th_conf_abst.html |archive-date= 2007-08-13 }}</ref> According to a series of experiments carried out in the late 1950s, called the [[AASHO Road Test]], it was empirically determined that the effective damage done to the road is roughly proportional to the [[fourth power]] of [[gross axle weight rating|axle weight]].<ref name="Motorway_Achievement_Pg252">{{cite book |author1=Ron Bridle |author2=John Porter |title= The Motorway Achievement: Frontiers of Knowledge and Practice |publisher= Thomas Telford |year= 2002 |page= 252 |url=https://books.google.com/books?id=7Yqxyefv-VAC&q=4th+power+of+axle+weight&pg=PA252 |isbn= 978-0-7277-3197-5 }}</ref> A typical [[semi-trailer truck|tractor-trailer]] weighing 80,000 [[pound (mass)|pounds]] (36.287 [[tonne|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]]s on roads are caused by rain damage and vehicle braking or related construction work.

[[File:Making lines on the road.JPG|thumb|upright|[[Road surface marking|Line marking]] in rural India]]

[[Road surface|Pavements]] are designed for an expected [[service life]] or [[design life]]. In some parts of the United Kingdom the standard design life is 40 years for new [[bitumen]] and concrete pavement. Maintenance is considered in the whole life cost of the road with service at 10, 20 and 30-year milestones.<ref name="Highways_The_Location">{{cite book |last= O'Flaherty |first= Coleman A. |title= Highways: The Location, Design, Construction & Maintenance of Road Pavements |publisher= Elsevier |year= 2002 |page= 252 <!-- different book different fact same page as ref Name="Motorway_Achievement_Pg252" --> |url=https://books.google.com/books?id=Ren4sWQ3jKkC&q=Pavements+are+designed+for+an+expected+service+life&pg=PA252 |isbn= 978-0-7506-5090-8 }}</ref> 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 concrete|asphalt]] pavements are designed as '''perpetual pavements''' with an expected structural life in excess of 50 years.<ref>{{cite book |last1= Newcomb |first1= David E. |last2= Willis |first2= Richard |last3= Timm |first3= David H. |title= Perpetual Asphalt Pavements: A Synthesis |publisher= Asphalt Pavement Alliance |year= 2010 |location= Lanham, Maryland |url=http://asphaltroads.org/images/documents/Perpetual_Pavement_Synthesis.pdf |access-date= 2013-01-22}}</ref>

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.<ref>{{cite web |url=http://asphaltroads.org/perpetual-pavement/award-winners.html |title= Perpetual Pavement Award Winners |access-date= 2013-01-22 |author= Asphalt Pavement Association}}</ref> Many concrete pavements built since the 1950s have significantly outlived their intended design lives.<ref name="Map_Future">{{cite web |author1= Theodore R. Ferragut |author2= Dale Harrington |author3= Marcia Brink |name-list-style= amp |title= Road Map to the Future |publisher= United States Department of Transportation – Federal Highway Administration |date= July–August 2002 |url=http://www.tfhrc.gov/pubrds/02jul/10.htm |access-date= 2007-05-13 |archive-url=https://web.archive.org/web/20070814113422/http://www.tfhrc.gov/pubrds/02jul/10.htm |archive-date= 2007-08-14 |url-status= dead }}</ref> Some roads like [[Chicago]]'s [[Wacker Drive]], a major two-level (and at one point, three-level) roadway in the downtown area, are being rebuilt with a designed service life of 100 years.<ref name="Fly_Ash">{{cite web |last= ISG Resources, Inc |title= Fly Ash Concrete Design for Chicago's 100-Year Road Structure |work= Case Study |publisher= U.S. Environmental Protection Agency |date= December 2003 |url=http://www.epa.gov/epaoswer/osw/conserve/c2p2/cases/wacker-dr.pdf |access-date= 2007-05-13 }}</ref>

Virtually all roads require some form of maintenance before they come to the end of their service life. Pro-active agencies use [[pavement management]] techniques to continually monitor road conditions and schedule [[preventive maintenance]] treatments as needed to prolong the lifespan of their roads. Technically advanced agencies monitor the road network surface condition with sophisticated equipment such as laser/inertial [[profilometer]]s. These measurements include road [[curvature]], [[cross slope]], [[Asperity (material science)|asperity]], [[surface roughness|roughness]], [[rut (roads)|rutting]] and [[texture (roads)|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 sealing, [[pavement milling|micro milling]] or [[diamond grinding of pavement|diamond grinding]] and [[Chipseal|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.<ref name="Thin_Surfacing">{{cite web |first1=Ludomir |last1=Uzarowski |first2=Michael |last2=Maher |first3=Gary |last3=Farrington |author4= Golder Associates Ltd. |title= Thin Surfacing – Effective Way of Improving Road Safety within Scarce Road Maintenance Budget |work= Paper for presentation at the 2005 Annual Conference of the Transportation Association of Canada in Calgary, Alberta |publisher= Transportation Association of Canada |year= 2005 |url=http://www.tac-atc.ca/english/pdf/conf2005/s16/uzarowski2.pdf |access-date= 2007-05-14 |archive-url=https://web.archive.org/web/20080407011631/http://www.tac-atc.ca/english/pdf/conf2005/s16/uzarowski2.pdf <!-- Bot retrieved archive --> |archive-date= 2008-04-07}}</ref>

Older concrete pavements that develop faults can be repaired with a [[dowel bar retrofit]], in which slots are cut in the pavement at each joint, and dowel bars are placed in the slots, which are then filled with concrete patching material. This can extend the life of the concrete pavement for 15 years.<ref>{{cite web|title=Dowel Bars for New and Existing Concrete Pavements|url=http://www.wsdot.wa.gov/NR/rdonlyres/0137787C-4E9A-408C-A9CA-ECC02878D623/0/DowelBarsfolio_March2013.pdf|publisher=Washington State Department of Transportation|access-date=24 March 2014|date=February 2013}}</ref>

Failure to maintain roads properly can create significant costs to society. A 2009 report released by the American Association of State Highway and Transportation Officials estimated that 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 (hydrology)|infiltration]]. The most common causes of voids are pumping, consolidation, subgrade failure and bridge approach failure. Slab stabilization is a non-destructive method of solving this problem and is usually employed with other [[concrete pavement restoration]] 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]] or [[polyurethane]] mixture through holes drilled through the slab. The grout can fill small voids beneath the slab and/or sub-base. The grout also displaces free water and helps keep water from saturating and weakening support under the joints and slab edge after stabilization is complete. The three steps for this method after finding the voids are locating and drilling holes, grout injection and post-testing the stabilized slabs.

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

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

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

Common stabilization materials include [[pozzolan]]-cement grout and polyurethane. The requirements for slab stabilization are strength and the ability to flow into or expand to fill small voids. Colloidal mixing equipment is necessary to use the pozzolan-cement grouts. The contractor must place the grout using a positive-displacement injection pump or a non-pulsing progressive cavity pump. A drill is also necessary but it must produce a clean hole with no surface [[spalling]] or breakouts. The injection devices must include a grout packer capable of sealing the hole. The injection device must also have a return hose or a fast-control reverse switch, in case workers detect slab movement on the uplift gauge. The uplift beam helps to monitor the slab deflection and has to have sensitive dial gauges.<ref name="igga">{{cite web|url=http://www.igga.net/File/Minnesota-State-Aid-Concrete-Pavement-Rehabilitation-CPR-Best-Practices-Manual-_2006.pdf |title=State Aid Concrete Pavement Rehabilitation Best Practices Manual 2006 |access-date=2013-05-13 |url-status=dead |archive-url=https://web.archive.org/web/20130809234355/http://www.igga.net/File/Minnesota-State-Aid-Concrete-Pavement-Rehabilitation-CPR-Best-Practices-Manual-_2006.pdf |archive-date=2013-08-09}} Minnesota DOT</ref><ref>"Practical guidelines for CPR of Urban Roads: A compelling need for preserving city concrete streets led to the development of a methodology for scoping repairs and the undertaking of a comprehensive concrete pavement repair program in Grand Rapids, Michigan". June 2005. ''Better Roads''.</ref>

===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 techniques. Successful resealing consists of old sealant removal, shaping and cleaning the reservoir, installing the backer rod and installing the sealant. Sawing, manual removal, plowing and cutting are methods used to remove the old sealant. Saws are used to shape the reservoir. When cleaning the reservoir, no dust, [[dirt]] or traces of old sealant should remain. Thus, it is recommended to water wash, sand-blast and then air blow to remove any sand, dirt or dust. The backer rod installation requires a double-wheeled, steel roller to insert the rod to the desired depth. After inserting the backer rod, the sealant is placed into the joint. There are various materials to choose for this method including hot pour bituminous liquid, silicone and preformed compression seals.<ref name="igga" /><ref>{{cite web |url=http://www.igga.net/File/Minimize-Wheel-Slap-Keep-Your-Joints-Narrow-_2004.pdf |title=Minimize Wheel-Slap: Keep Your Joints Narrow |access-date=2010-01-06 |url-status=dead |archive-url=https://web.archive.org/web/20110723154515/http://www.igga.net/File/Minimize-Wheel-Slap-Keep-Your-Joints-Narrow-_2004.pdf |archive-date=2011-07-23 }} IGGA</ref><ref>How States Preserve Concrete Pavements: CPR pays off in extra pavement life. Better Roads. August 2005.</ref><ref>CPR brings dying pavement back to life: Georgia continues to be the leader in concrete pavement restoration, but as the word spreads other states are beginning to use this system to restore deteriorating pavements. April 1997, Roads & Bridges Magazine</ref>

==Safety considerations==
{{see also|Road traffic safety}}
[[File:Wavy lines before pedestrian crossing.jpg|thumb|[[Pedestrian crossing]], line markings and [[street furniture]] ]]
Careful design and construction of roads can increase [[road traffic safety]] and reduce the harm (deaths, injuries, and property damage) on the highway system from traffic collisions.

On neighborhood roads [[traffic calming]], [[safety barriers]], pedestrian crossings and cycle lanes can help protect pedestrians, cyclists, and drivers.

Lane markers in some countries and states are marked with [[Cat's eye (road)|Cat's eyes]] or Botts dots. 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 road|limited access]] from properties and local roads, [[Grade separation|grade separated junctions]] and [[Dual carriageway|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]] 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 is not higher than the surrounding landscape, it may result in flooding.<ref>{{cite book|last1=Neteler|first1=Markus|title=Open Source GIS: A GRASS GIS Approach|url=https://archive.org/details/opensourcegisgra00nete_842|url-access=limited|date=2007|page=[https://archive.org/details/opensourcegisgra00nete_842/page/n163 149]}}</ref>

[[Speed limits]] can improve road traffic safety and reduce the number of [[Epidemiology of motor vehicle collisions|road traffic casualties]] from [[traffic collisions]]. In their ''World report on road traffic injury prevention'' report, the [[World Health Organization|World Health Organization (WHO)]] identify speed control as one of various interventions likely to contribute to a reduction in road casualties.

==Road conditions==
[[File:Snowy road in Tieringen, Baden-Württemberg.jpg|thumb|[[Snow]] causing bad 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 [[Road surface|pavement surface]], [[pothole]]s, road markings, and [[weather]]. It has been reported that "[p]roblems of transportation participants and road conditions are the main factors that lead to road traffic accidents".<ref>Yafeng Yin, Jian Lu, Wei Wang, ''Icctp 2011: Towards Sustainable Transportation Systems'' (2011), p. 1807.</ref> It has further been specifically noted that "weather conditions and road conditions are interlinked as weather conditions affect the road conditions".<ref>Radu Popescu-Zeletin, Karl Jonas, Idris A. Rai, ''e-Infrastructure and e-Services for Developing Countries'' (2012), p. 141.</ref> Specific aspects of road conditions can be of particular importance for particular purposes. For example, for [[autonomous vehicles]] such as [[self-driving car]]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".<ref>IEEE ITSS, ''IEEE Intelligent Vehicles Symposium'' (2005), p. 154.</ref>

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.<ref>Fred Bayles, ''Field Guide to Covering Local News'' (2012), p. 1.</ref>

==Environmental performance==
{{Main|Environmental impacts of roads}}
[[File:Aab Pasadena Highway Los Angeles.jpg|thumb|Air pollution along Pasadena Highway in Los Angeles]]
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.<ref>{{Cite book|url=https://books.google.com/books?id=cdc3AQAAMAAJ&q=Drainage+systems+can+be+used+to+reduce+the+effect+of+pollutants+from+roads&pg=PA293|title=Pittsburgh Light Rail Transit Reconstruction: Environmental Impact Statement|date=1979|publisher=The Administration|language=en}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=9o7rq6WnSXEC&q=Drainage+systems+can+be+used+to+reduce+the+effect+of+pollutants+from+roads&pg=PA312|title=The Ecology of Transportation: Managing Mobility for the Environment|last1=Davenport|first1=John|last2=Davenport|first2=Julia L.|year=2006|publisher=Springer Science & Business Media|isbn=978-1-4020-4504-2|language=en}}</ref> [[Rain]]water and [[snowmelt]] running off of roads tends to pick up gasoline, [[motor oil]], [[heavy metals]], [[waste|trash]] and other pollutants and result in [[water pollution]]. Road runoff is a major source of [[nickel]], copper, [[zinc]], [[cadmium]], lead and [[polycyclic aromatic hydrocarbon]]s (PAHs), which are created as [[combustion]] byproducts of gasoline and other [[fossil fuel]]s.<ref>{{cite book |title=Stormwater Effects Handbook: A Toolbox for Watershed Managers, Scientists, and Engineers |publisher=CRC/Lewis Publishers |location=New York |year=2001 |isbn=978-0-87371-924-7 |chapter-url=http://unix.eng.ua.edu/~rpitt/Publications/BooksandReports/Stormwater%20Effects%20Handbook%20by%20%20Burton%20and%20Pitt%20book/MainEDFS_Book.html |first1=G. Allen Jr. |last1=Burton |first2=Robert |last2=Pitt |chapter=2 |access-date=2009-04-30 |archive-date=2009-05-19 |archive-url=https://web.archive.org/web/20090519035716/http://unix.eng.ua.edu/~rpitt/Publications/BooksandReports/Stormwater%20Effects%20Handbook%20by%20%20Burton%20and%20Pitt%20book/MainEDFS_Book.html |url-status=dead }}</ref>

[[De-icing]] chemicals and sand can run off into roadsides, contaminate [[groundwater]] and pollute [[surface water]]s;<ref>Charles Seawell and Newland Agbenowosi (1998). [http://www.cee.vt.edu/ewr/environmental/teach/gwprimer/roadsalt/roadsalt.html "Effects of Road Deicing Salts on Groundwater Systems."] {{webarchive |url=https://web.archive.org/web/20090521095505/http://www.cee.vt.edu/ewr/environmental/teach/gwprimer/roadsalt/roadsalt.html |date=2009-05-21 }} Virginia Polytechnic Institute, Department of Civil Engineering.</ref> and [[road salt]]s can be toxic to sensitive plants and animals.<ref>University of Minnesota (2009). [http://www1.umn.edu/news/news-releases/2009/UR_RELEASE_MIG_5295.html "U of M research finds most road salt is making it into the state's lakes and rivers."] 2009-02-10.</ref> Sand applied to icy roads can be ground up by traffic into fine particulates and contribute to air pollution.

Roads are a chief source of [[noise pollution]]. In the early 1970s, it was recognized{{by whom|date=April 2018}} that design of roads can be conducted to influence and minimize noise generation.<ref>{{cite journal |url=https://doi.org/10.1007%2FBF00159677 | doi=10.1007/BF00159677 | title=Analysis of highway noise | year=1973 | last1=Hogan | first1=C. Michael | journal=Water, Air, and Soil Pollution | volume=2 | issue=3 | pages=387–392 | bibcode=1973WASP....2..387H | s2cid=109914430 }}</ref> [[Noise barrier]]s can reduce noise pollution near built-up areas. Regulations can restrict the use of [[engine braking]].

[[Motor vehicle emissions]] contribute [[air pollutant|air pollution]]. Concentrations of air pollutants and adverse [[respiratory]] health effects are greater near the road than at some distance away from the road.<ref name="carbonblack">{{cite web |title= Traffic-related Air Pollution near Busy Roads |publisher= American Journal of Respiratory and Critical Care Medicine Vol 170. pp. 520–26 |year= 2004 |url=http://ajrccm.atsjournals.org/cgi/content/full/170/5/520 }}</ref> [[Road dust]] kicked up by vehicles may trigger [[allergic]] reactions.<ref>[https://www.sciencedaily.com/releases/1999/11/991130062843.htm "Road Dust – Something To Sneeze About."] ''Science Daily,'' 1999-11-30.</ref> In addition, on-road transportation greenhouse gas emissions are the largest single cause of climate change, scientists say.<ref>{{cite journal|title=Attribution of climate forcing to economic sectors |doi=10.1073/pnas.0906548107 |pmid=20133724 |volume=107 |issue=8 |journal=Proceedings of the National Academy of Sciences |pages=3382–87|year=2010 |last1=Unger |first1=N. |last2=Bond |first2=T.C. |last3=Wang |first3=J.S. |last4=Koch |first4=D.M. |last5=Menon |first5=S. |last6=Shindell |first6=D.T. |last7=Bauer |first7=S. |pmc=2816198 |bibcode=2010PNAS..107.3382U |doi-access=free }}</ref>

==Regulation==
===Right- and left-hand traffic===
{{Main|Right- and left-hand traffic}}
[[File:Roadmumbaiindia.jpg|thumb|upright|A city street in [[Mumbai, India]] with left-hand traffic]]
Traffic flows on the right or on the left side of the road depending on the country.<ref name="Why_In_Britain">{{cite web |author= Ray |title= Why In Britain Do We Drive On The Left? |publisher= 2Pass.co.uk |date= 2007 |url=http://www.2pass.co.uk/goodluck.htm |access-date= 2007-03-24 }}</ref> In countries where traffic flows on the right, traffic signs are mostly on the right side of the road, [[roundabout]]s and [[traffic circle]]s go counter-clockwise/anti-clockwise, and pedestrians crossing a two-way road should watch out for traffic from the left first.<ref name="Rule_of_the_Road">{{cite book |last= Kincaid |first= Peter |title= The Rule of the Road: An International Guide to History and Practice |publisher= Greenwood Press |year= 1986 |isbn= 978-0-313-25249-5 }}</ref> 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,<ref name="brianlucas">{{cite web |last=Lucas |first=Brian |year=2005 |url=http://www.brianlucas.ca/roadside/ |title= Which side of the road do they drive on?
|access-date=2006-08-03}}</ref> even though originally most traffic drove on the left worldwide.<ref>{{Cite web|url=http://users.pandora.be/worldstandards/driving%20on%20the%20left.htm|title=Why do some countries drive on the right and others on the left ?}}</ref>

==Economics==
{{Main|Transport economics}}

[[Transport economics]] is used to understand both the relationship between the transport system and the wider economy and the complex effects of the road network structure when there are multiple paths and competing modes for both personal and freight (road/rail/air/ferry) and where [[induced demand]] can result in increased on decreased transport levels when road provision is increased by building new roads or decreased (for example California State Route 480). Roads are generally built and maintained by the [[public sector]] using taxation although implementation may be through [[private sector|private]] [[General contractor|contractors]]).<ref name="Australia_CCG_2004">{{cite web |author= www.stat-usa.gov/ |title= International Market Research Reports |work= Australia CCG 2004 Update: Economic Trends and Outlook (E. Infrastructure ) |publisher= Industry Canada |date= 2006-02-28 |url=http://strategis.ic.gc.ca/epic/site/imr-ri.nsf/en/gr126748e.html |access-date= 2007-04-17 |archive-url=https://web.archive.org/web/20071114181049/http://strategis.ic.gc.ca/epic/site/imr-ri.nsf/en/gr126748e.html <!-- Bot retrieved archive --> |archive-date= 2007-11-14}}</ref><ref name="ARTBA">{{cite web |title= State and Federal Gasoline Taxes |work= Maps, Reports and history of gas tax in the United States |publisher= American Road & Transportation Builders Association ("ARTBA") |url=http://www.artba.org/economics_research/current_issues/state_fed_gas_taxes.htm |access-date= 2007-05-02 |archive-url=https://web.archive.org/web/20070408082904/http://www.artba.org/economics_research/current_issues/state_fed_gas_taxes.htm <!-- Bot retrieved archive --> |archive-date= 2007-04-08}}</ref> or occasionally using [[toll road|road tolls]].<ref name="IBTTA">{{cite web |title= International Bridge, Tunnel and Turnpike Association |date=April 16, 2007 |url=http://ibtta.org/ |access-date= 2007-04-17 }}</ref>

[[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:<ref>{{cite journal|last=Cardno|first=Catherine|title=Infrastructure: New Report Examines the Potential of Public-Private Partnerships for Transportation Infrastructure|journal=Civil Engineering|year=2008|volume=78|issue=11|issn=0885-7024}}</ref>
* design/build
* design/build/operate/maintain
* design/build/finance/operate
* build/own/operate

Society depends heavily on efficient roads. In the [[European Union|European Union (EU)]] 44% of all [[Good (economics)|goods]] are moved by trucks over roads and 85% of all people are transported by cars, buses or coaches on roads.<ref name="Road_Transport_(Europe)">{{cite web |title= Road Transport (Europe) |work= Overview |publisher= European Communities, Transportation |date= 2007-02-15 |url=http://ec.europa.eu/transport/road/index_en.htm |access-date= 2007-03-24 |url-status=dead |archive-url=https://web.archive.org/web/20070315230823/http://ec.europa.eu/transport/road/index_en.htm |archive-date= 2007-03-15 }}</ref> The term was also commonly used to refer to [[roadstead]]s, waterways that lent themselves to use by shipping.

===Construction costs===
According to the New York State Thruway Authority,<ref>
{{cite web |title= Thruway Fact Book |publisher= New York State Thruway Authority |url=http://www.thruway.ny.gov/about/factbook/ |access-date= 2011-05-05 |url-status=dead |archive-url=https://web.archive.org/web/20110502030241/http://www.thruway.ny.gov/about/factbook/ |archive-date= 2011-05-02 }}
</ref> some sample per-mile costs to construct multi-lane roads in several US northeastern states were:
* [[Connecticut Turnpike]] – $3,449,000 per mile
* [[New Jersey Turnpike]] – $2,200,000 per mile
* [[Pennsylvania Turnpike]] (Delaware Extension) – $1,970,000 per mile
* [[Indiana Toll Road|Northern Indiana Toll Road]] – $1,790,000 per mile
* [[Garden State Parkway]] – $1,720,000 per mile
* [[Massachusetts Turnpike]] – $1,600,000 per mile
* Thruway, New York to Pennsylvania Line – $1,547,000 per mile
* [[Ohio Turnpike]] – $1,352,000 per mile
* [[Pennsylvania Turnpike]] (early construction) – $736,000 per mile

==Statistics==
The United States has the largest network of roads of any country with {{convert|4050717|mi}} as of 2009.<ref>{{Cite web|url=http://www.bts.gov/publications/national_transportation_statistics/html/table_01_01.html|title=Research and Innovative Technology Administration Bureau of Transportation Statistics U.S. mileage table|access-date=2012-01-09|archive-url=https://web.archive.org/web/20080418081336/http://www.bts.gov/publications/national_transportation_statistics/html/table_01_01.html|archive-date=2008-04-18|url-status=dead}}</ref> The Republic of India has the second-largest road system globally with {{convert|4689842|km|mi|abbr=off}} of road (2013).<ref>{{cite web |url=http://164.100.47.134/intranet/NHDP.pdf |title=National Highways Development Project: An Overview |access-date=2014-06-07 |url-status=dead |archive-url=https://web.archive.org/web/20140714152629/http://164.100.47.134/intranet/NHDP.pdf |archive-date=2014-07-14 }}</ref> The People's Republic of China is third with {{convert|3583715|km}} of road (2007). The Federative Republic of Brazil has the fourth-largest road system in the world with {{convert|1751868|km}} (2002). See [[List of countries by road network size]]. When looking only at [[Controlled-access highway|expressways]], the [[National Trunk Highway System]] (NTHS) in China has a total length of {{convert|45000|km}} at the end of 2006, and 60,300&nbsp;km at the end of 2008, second only to the United States with {{convert|90000|km}} in 2005. However, as of 2017, China has 130,000&nbsp;km of Expressways.<ref>{{Cite web|url=http://en.people.cn/200612/30/eng20061230_337130.html|title=People's Daily Online &ndash; China to build more highways in 2007|website=en.people.cn}}</ref><ref>{{cite web|url=http://www.chinagate.com.cn/english/45626.htm|title=Expressways Being Built at Frenetic Pace|access-date=10 January 2017|url-status=dead|archive-url=https://web.archive.org/web/20070701114053/http://www.chinagate.com.cn/english/45626.htm|archive-date=1 July 2007}}</ref>

==Global connectivity==
[[File:Hailuoto Ice Road 20130113 05.JPG|thumb|[[Ice road]] between [[Oulunsalo]] and [[Hailuoto]] in [[North Ostrobothnia]], Finland]]
Eurasia, Africa, North America, South America, and Australia each have an extensive road network that connects most cities.
The North and South American road networks are separated by the [[Darién Gap]], the only interruption in the [[Pan-American Highway]]. Eurasia and Africa are connected by roads on the [[Sinai Peninsula]]. The [[European Peninsula]] is connected to the [[Scandinavian Peninsula]] by the [[Øresund Bridge]], and both have many connections to the mainland of Eurasia, including the bridges over the [[Bosphorus]]. [[Antarctica]] has very few roads and no continent-bridging network, though there are a few [[ice road]]s between bases, such as the [[South Pole Traverse]]. [[Bahrain]] is the only [[island country]] to be connected to a continental network by road (the [[King Fahd Causeway]] to Saudi Arabia).

Even well-connected road networks are controlled by many different legal jurisdictions, and laws such as [[Right- and left-hand traffic|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 {{cvt|113|mi|adj=on}} [[Overseas Highway]] connecting many of the [[Florida Keys]] with the continental United States.

Even on mainlands, some [[List of cities that are inaccessible by road|settlements have no roads]] connecting with the primary continental network, due to natural obstacles like mountains or wetlands, or high cost compared to the population served. Unpaved roads or lack of roads are more common in [[developing countries]], and these can become impassible in wet conditions. As of 2014, only 43% of rural Africans have access to an all-season road.<ref>{{cite book |url=https://www.afdb.org/fileadmin/uploads/afdb/Documents/Publications/Tracking_Africa’s_Progress_in_Figures.pdf |title=Tracking Agrica's Progress in Figures |year=2014 |publisher=[[African Development Bank]] |pages=71 }}</ref> Due to steepness, mud, snow, or fords, roads can sometimes be passable only to [[four-wheel drive]] vehicles, those with [[snow chain]]s or [[snow tire]]s, or those capable of [[deep wading]] or [[Amphibious vehicle|amphibious operation]].

Most disconnected settlements have local road networks connecting ports, buildings, and other points of interest.

Where demand for travel by road vehicle to a disconnected island or mainland settlement is high, [[roll-on/roll-off]] ferries are commonly available if the journey is relatively short. For long-distance trips, passengers usually travel by air and [[car rental|rent a car]] upon arrival. If facilities are available, vehicles and cargo can also be shipped to many disconnected settlements by boat, or air transport at much greater expense. The island of [[Great Britain]] is connected to the European road network by [[Eurotunnel Shuttle]] – an example of a [[car shuttle train]] which is a service used in other parts of Europe to travel under mountains and over wetlands.

In polar areas, disconnected settlements are often more easily reached by [[snowmobile]] or [[dogsled]] in cold weather, which can produce [[sea ice]] that blocks ports, and bad weather that prevents flying. For example, resupply aircraft are only flown to [[Amundsen–Scott South Pole Station]] October to February, and many residents of coastal Alaska have bulk cargo shipped in only during the warmer months. Permanent darkness during the winter can also make long-distance travel more dangerous in polar areas. Continental road networks do reach into these areas, such as the [[Dalton Highway]] to the North Slope of Alaska, the [[R21 highway (Russia)|R21 highway]] to [[Murmansk]] in Russia, and many roads in Scandinavia (though due to [[fjord]]s water transport is sometimes faster). Large areas of Alaska, Canada, Greenland, and [[Siberia]] are sparsely connected. For example, all 25 communities of [[Nunavut]] are disconnected from each other and the main North American road network.<ref>{{cite web |url=http://nunavuttourism.com/planning-your-trip/how-to-get-here |work=Nunavut Tourism |title=How to Get Here |access-date=10 January 2017 |publisher=[[Canadian Northern Economic Development Agency]]}}</ref>

Road transport of people and cargo by may also be obstructed by [[border control]]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 [[list of car-free places|car-free]], and roads (if present) might be used by bicycles or pedestrians.

Roads are under construction to many remote places, such as the villages of the [[Annapurna Circuit]], and a road was completed in 2013 to [[Mêdog County]]. Additional [[intercontinental and transoceanic fixed links]] have been proposed, including a [[Bering Strait crossing]] that would connect Eurasia-Africa and North America, a [[Malacca Strait Bridge]] to the largest island of [[Indonesia]] from Asia, and a [[Strait of Gibraltar crossing]] to connect Europe and Africa directly.

==See also==
{{Portal|Roads}}
* [[Glossary of road transport terms]]
* [[Highway engineering]]
* [[Issue tracking system#Government|Issue tracking systems for reporting road defects]]
* [[List of countries by road network size]]
* [[List of roads and highways]]
* [[Road transport]]
* [[Trade route]]

==References==
{{Reflist}}

{{Infrastructure}}
{{Road}}
{{Geotechnical engineering}}

{{Authority control}}

[[Category:Roads| ]]
[[Category:Infrastructure]]
[[Category:Types of roads]]