Editing Road (section)

==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 "Gravel Driveway Construction: Step by Step Guide: How to Lay a Gravel Driveway"] 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.