Roads in Lassen County, California

A road is a linear way for the conveyance of traffic that mostly has an improved surface for use by vehicles (motorized and non-motorized) and pedestrians. Unlike streets, the main function of roads is transportation.

There are many types of roads, including parkways, avenues, controlled-access highways (freeways, motorways, and expressways), tollways, interstates, highways, thoroughfares, and local roads.

The primary features of roads include lanes, sidewalks (pavement), roadways (carriageways), medians, shoulders, verges, bike paths (cycle paths), and shared-use paths.

Definitions

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

The Organization for Economic Co-operation and Development (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, ITF and UNECE ''Glossary for Transport Statistics Illustrated'' defines a road as a "Line of communication (traveled way) open to public traffic, primarily for the use of road motor vehicles, using a stabilized base other than rails or air strips. ..Included are paved roads and other roads with a stabilized base, e.g. gravel roads. Roads also cover streets, bridges, tunnels, supporting structures, junctions, crossings and interchanges. Toll roads are also included. Excluded are dedicated cycle lanes."

The 1968 Vienna Convention on Road Traffic defines a road as the entire surface of any way or street open to public traffic.

In urban areas roads may diverge through a city or village and be named as streets, serving a dual function as urban space easement and route. Modern roads are normally smoothed, paved, or otherwise prepared to allow easy travel.

Australia

Part 2, Division 1, clauses 11-13 of the National Transport Commission Regulations 2006 defines a road in Australia as 'an area that is open to or used by the public and is developed for, or has as one of its main uses, the driving or riding of motor vehicles.'

Further, it defines a shoulder (typical an area of the road outside the edge line, or the curb) and a road-related area which includes green areas separating roads, areas designated for cyclists and areas generally accessible to the public for driving, riding or parking vehicles.

New Zealand

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

United Kingdom

In the United Kingdom ''The Highway Code'' details rules for "road users", but there is some ambiguity between the terms ''highway'' and ''road''. 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". This includes footpaths, bridleways and cycle tracks, and also road and driveways on private land and many car parks. Vehicle Excise Duty, a road use tax, is payable on some vehicles used on the public road.

The definition of a road depends on the definition of a highway; there is no formal definition for a highway in the relevant Act. A 1984 ruling said "the land over which a public right of way exists is known as a highway; and although most highways have been made up into roads, and most easements of way exist over footpaths, the presence or absence of a made road has nothing to do with the distinction. Another legal view is that while a highway historically included footpaths, bridleways, driftways, etc., it can now be used to mean those ways that allow the movement of motor vehicles, and the term ''rights of way'' can be used to cover the wider usage.

United States

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

History

The assertion that the first pathways were the trails made by animals has not been universally accepted; in many cases animals do not follow constant paths. Some believe that some roads originated from following animal trails. The Icknield Way may exemplify this type of road origination, where human and animal both selected the same natural line. By about 10,000 BC human travelers used rough roads/pathways.
* The world's oldest known paved road was constructed in Egypt some time between 2600 and 2200 BC.
* Stone-paved streets appear in the city of Ur in the Middle East dating back to 4000 BC.
* Corduroy roads (log roads) are found dating to 4000 BC in Glastonbury, England.
* The Sweet Track, a timber track causeway in England, is one of the oldest engineered roads discovered and the oldest timber trackway discovered in Northern Europe. Built in winter 3807 BC or spring 3806 BC, (tree-ring dating – dendrochronology – 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, London.
* Brick-paved streets appeared in India as early as 3000 BC.
* 1995 BC: an early subdividing of roadways evidenced with sidewalks built in Anatolia.
* 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, 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.
* 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 carts and river barges. A hybrid of road transport and ship transport beginning in about 1740 is the horse-drawn boat in which the horse follows a cleared path along the river bank.
* From about 312 BC, the Roman Empire built straight strong stone Roman roads throughout Europe and North Africa, in support of its military campaigns. At its peak the Roman Empire was connected by 29 major roads moving out from Rome and covering 78,000 kilometers or 52,964 Roman miles of paved roads.
* In the 8th century AD, many roads were built throughout the Arab Empire. The most sophisticated roads were those in Baghdad, which were paved with tar. Tar was derived from petroleum, accessed from oil fields in the region, through the chemical process of destructive distillation.
* The Highways Act 1555 in Britain transferred responsibility for maintaining roads from government to local parishes. This resulted in a poor and variable state of roads. To remedy this, the first of the turnpike trusts was established around 1706, to build good roads and collect tolls from passing vehicles. Eventually there were approximately 1,100 trusts in Britain and some 36,800 km (22,870 miles) of engineered roads. The Rebecca Riots in Carmarthenshire and Rhayader from 1839 to 1844 contributed to a Royal Commission that led to the demise of the system in 1844,

which coincided with the development of the UK railway system.
* In the late-19th century roading engineers began to cater for cyclists by building separate lanes alongside roadways.
* From the beginning of the 20th century, roads were increasingly built for tourism and also to create jobs. A typical example of the stimulation of tourism is the Great Dolomite Road, while the creation of the panoramic coastal road Strada Costiera between Duino and Barcola in 1928 was very much focused on creating jobs.

Design

Road design is part of highway engineering. Structural road design is designing a road for the environment in order to extend its longevity and reduce maintenance. The Shell pavement design method is used in many countries for the design of new asphalt roadsides.

Terminology

;Adverse camber: Where a road slopes towards the outside of a bend, increasing the likelihood that vehicles travelling at speed will skid or topple. Usually only a temporary situation during road maintenance.
;Alignment: The route of the road, defined as a series of horizontal tangents and curves.
;All-weather road: Unpaved road that is constructed of a material that does not create mud during rainfall.
;Banked turn
;Belisha Beacon: An orange globe, lit at night, used to highlight a pedestrian crossing
;Bicycle boulevard: A street that allows local vehicle traffic, but is prioritized for bicycles and other non-motorized travel
;
;Bollard: 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: 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 used on roads
;Camber (or crown): The slope of the road surface downwards away from the centre of the road, so that surface water can flow freely to the edge of the carriageway, or on bends angling of the surface to lean traffic 'into the bend' reducing the chance of a skid.
;Cant: Another name for cross slope or camber
;Carriageway: Part of the road intended for the movement of road motor vehicles; the parts of the road which form a shoulder for the lower or upper layers of the road surface are not part of the roadway, nor are those parts of the road intended for the circulation of road vehicles which are not self-propelled or for the parking of vehicles.
; Cat's eye: Reflective raised pavement marker used on roads
;Chicane: Sequence of tight serpentine curves (usually an S-shape curve or a bus stop)
;Chipseal: Road surface composed of a thin layer of crushed stone 'chips' and asphalt emulsion. It seals the surface and protects it from weather, but provides no structural strength. It is cheaper than asphalt concrete or concrete. In the United States, it is usually only used on low volume rural roads
;Corniche: Road on the side of a cliff or mountain, with the ground rising on one side and falling away on the other
;Cross slope: The slope of the pavement, expressed as units of rise per unit of run, or as a percentage
;Curb (kerb): A raised edge at the side of the roadway.
;Curb extension: (also kerb extension, bulb-out, nib, elephant ear, curb bulge and blister) Traffic calming measure, intended to slow the speed of traffic and increase driver awareness, particularly in built-up and residential neighborhoods.
;Cycle lane: Part of a carriageway designated for cycles and distinguished from the rest of the carriageway by longitudinal road markings. Mopeds may also be allowed to use a cycle lane.
;Cycle track: Independent road or part of a road designated for cycles and sign-posted as such. A cycle track is separated from other roads or other parts of the same road by structural means. Mopeds may also be allowed to use the cycle track.
;Cycling infrastructure: Cycling-friendly infrastructure integrated into the roadway or in its own right of way
;Drainage gradient
;Farm-to-market road: A state road or county road that connects rural or agricultural areas to market towns.
;Fork: (literally "fork in the road") Type of intersection where a road splits
;Grade: Longitudinal slope
; Green lane: (UK) Unsurfaced road, may be so infrequently used that vegetation colonises freely, hence 'green'. Many green lanes are ancient routes that have existed for millennia.
;Guide rail: Prevents vehicles from veering off the road into oncoming traffic, crashing against solid objects or falling from a road. Also called a guard rail or traffic barrier.
;Gutter: A drainage channel usually at the edge of the road or along a median.
;Interstate Highway System (United States): System of Interstate and Defense Highways
;Lane: One of the longitudinal strips into which a carriageway is divisible, whether or not defined by longitudinal road markings, which is wide enough for one moving line of motor vehicles other than motorcycles.
;Layby (Pullout, pull-off): A paved area beside a main road where cars can stop temporarily to let another car pass.
;Loose chippings: The hazard of stone chippings that have come loose
;Median: On dual carriageway roads, including controlled-access highways, divided highways and many limited-access roads, the central reservation (British English), median (North American English), median strip (North American English and Australian English), neutral ground ouisiana Englishor central nature strip (Australian English): Area that separates opposing lanes of traffic
;Motorway: (Europe) (Freeways in the US, Special road in the UK) Road, specially designed and built for motor traffic, which does not serve properties bordering on it, with separate carriageways for traffic in two directions, with no crossings at the same level (road, railway, tramway track, or footpath) and sign-posted as a motorway and is reserved for specific categories of road motor vehicles.
;Mountain pass: A relatively low-level route through a range of mountains
;Milestone: One of a series of numbered markers placed along a road, often at regular intervals, showing the distance to destinations.
;National Highway: Road built and maintained by a national authority.
; Pavement: The road regarded as a geoconstruction. In the UK the term is road surface and the pavement is a pedestrian walkway alongside the road.
;Pedestrian crossing: Designated point on a road where road marking or other means helps pedestrians cross safely
;Pelican crossing: (officially ''Pelicon crossing'') (UK) A PEdestrian LIght CONtrolled crossing.
;Private highway: Highway owned and operated for profit by private industry
;Private road: Road owned and maintained by a private individual, organization, or company rather than by a government
;Profile: The vertical alignment of a road, expressed as a series of grades, connected by parabolic curves.
; Protected Intersections for Bicycles
:A much safer design with a corner refuge island, a setback crossing of the pedestrians and cyclists, generally between 1.5–7 metres of setback, a forward stop bar, which allows cyclists to stop for a traffic light well ahead of motor traffic who must stop behind the crosswalk. Separate signal staging or at least an advance green for cyclists and pedestrians is used to give cyclists and pedestrians no conflicts or a head start over traffic. The design makes a right turn on red, and sometimes left on red depending on the geometry of the intersection in question, possible in many cases, often without stopping.
; Protected Bicycle Path: Cyclists ideally have a protected bike lane on separated by a concrete median with splay kerbs if possible, and have a protected bike lane width of at least 2 metres if possible (one way). In the Netherlands, most one-way cycle paths are at least 2.5 metres wide.
;Public space: Place where anyone has a right to come without being excluded because of economic or social conditions
;Ranch road: U.S. road that connects rural and agricultural areas to market towns
; Road number: Often assigned to identify a stretch of public roads – often dependent on the type of road, with numbers differentiating between interstates, motorways, arterial thoroughfares, etc.
;Road-traffic safety: Process to reduce the harm (deaths, injuries, and property damage) that result from vehicle crashes on public roads
;Roadworks: Part or all of the road is occupied for work or maintenance
; Roughness: Deviations from a true planar pavement surface, which affects vehicle suspension deflection, dynamic loading, ride quality, surface drainage and winter operations. Roughness have wavelengths ranging from 500 mm up to some 40 m. The upper limit may be as high as 350 m when considering motion sickness aspects; motion sickness is generated by motion with down to 0.1 Hz frequency; in an ambulance car driving 78 mph (126 km/h), waves with up to 350 m will excite motion sickness.
;Roundabout: A road junction where typically three or more roads are joined by a circular section of road. Traffic 'on the roundabout' has priority over traffic on approach roads, unless indicated otherwise. In countries where traffic drives on the left the roundabout is traveled in a clockwise direction. Also known as an ''island'' in parts of the UK.
; Segregated Bicycle Path: Cyclists ideally have a protected bike lane separated by a concrete median with splay kerbs if possible, and have a protected bike lane width of at least 2 meters if possible (one way). In the Netherlands, most one-way cycle paths are at least 2.5 metres wide.
;Shoulder (also hard shoulder): A clear, level area to the side of the roadway available for stopping if needed.
;State highway: Road numbered by the state, falling below numbered national highways (like U.S. Routes) in the hierarchy ''or'' a road maintained by the state, including nationally numbered highways
;Traffic: Pedestrians, ridden or herded animals, vehicles, bicycles, and other conveyances using any road for purposes of travel.
;Texture (roads): Deviations from a true planar pavement surface, which affects the interaction between road and tire. Microtexture have wavelengths below 0.5 mm, Macrotexture below 50 mm and Megatexture below 500 mm.
;Traffic calming: Set of strategies used by urban planners and traffic engineers to slow down or reduce motor vehicle traffic, thereby improving safety for pedestrians and bicyclists and improving the environment for residents
;Traffic island: (UK) A small raised area used to help define the traffic flow, which may also act as a refuge for pedestrians crossing the carriageway or a location for signs, barriers or lights – a synonym for roundabout in some parts of the UK
;Traffic light: Also known as a traffic signal, stop light, stop-and-go lights – a signaling device at a road intersection, pedestrian crossing, or other location that assigns right of way to different approaches to an intersection
;Zebra crossing (UK): A pedestrian crossing marked by black and white stripes on the carriageway

Construction

In transport engineering, subgrade is the native material underneath a constructed road.

Road construction requires the creation of an engineered continuous right-of-way or roadbed, overcoming geographic obstacles and having grades low enough to permit vehicle or foot travel, and may be required to meet standards set by law or official guidelines. The process is often begun with the removal of earth and rock by digging or blasting, construction of embankments, bridges and tunnels, and removal of vegetation (this may involve deforestation) and followed by the laying of pavement material. A variety of road building equipment is employed in road building.

After design, approval, planning, legal, and environmental considerations have been addressed alignment of the road is set out by a surveyor. The radii and gradient are designed and staked out to best suit the natural ground levels and minimize the amount of cut and fill. Great care is taken to preserve reference Benchmarks

Roads are designed and built for primary use by vehicular and pedestrian traffic. Storm drainage and environmental considerations are a major concern. Erosion and sediment controls are constructed to prevent detrimental effects. Drainage lines are laid with sealed joints in the road easement with runoff coefficients and characteristics adequate for the land zoning and storm water system. Drainage systems must be capable of carrying the ultimate design flow from the upstream catchment with approval for the outfall from the appropriate authority to a watercourse, creek, river or the sea for drainage discharge.

A borrow pit (source for obtaining fill, gravel, and rock) and a water source should be located near or in reasonable distance to the road construction site. Approval from local authorities may be required to draw water or for working (crushing and screening) of materials for construction needs. The topsoil and vegetation is removed from the borrow pit and stockpiled for subsequent rehabilitation 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

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