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A road is a thoroughfare, route, or way on land between two places that has been paved or otherwise improved to allow travel by foot or some form of conveyance, including a motor vehicle, cart, bicycle, or horse.


Roads consist of one or two roadways (British English: carriageways), each with one or more lanes and any associated sidewalks (British English: pavement) and road verges. There is sometimes a bike path. Other names for roads include parkways, avenues, freeways, tollways, interstates, highways, or primary, secondary, and tertiary local roads.


A bricked road in Bangladesh Road side view at chalna, Khulna - 33.jpg
A bricked road in Bangladesh
A gravel road in Namibia Gravel road, Namibia.jpg
A gravel road in Namibia

Historically many roads were simply recognizable routes without any formal construction or maintenance. [1]

The Organisation 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". [2]

The Eurostat, ITF and UNECE Glossary for Transport Statistics Illustrated defines a road as a "Line of communication (travelled 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." [3]

The 1968 Vienna Convention on Road Traffic defines a road as the entire surface of any way or street open to public traffic. [4]

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. [5] Modern roads are normally smoothed, paved, or otherwise prepared to allow easy travel. [6]


Part 2, Division 1, clauses 11-13 of the National Transport Commission Road Transport Legislation 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.' [7]

Further, it defines a shoulder (typical an area of the road outside the edge line, or the kerb) 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 [8] where the statutory definition includes areas the public has access to, by right or not. [9] Beaches, publicly accessible car parks and yards (even if privately owned), river beds, road shoulders (verges), wharves and bridges are included. [10] 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. [11] 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". [12] This includes footpaths, bridleways and cycle tracks, and also road and driveways on private land and many car parks. [13] Vehicle Excise Duty, a road use tax, is payable on some vehicles used on the public road. [13]

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. [14] [15] 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. [16]

United States

In the United States, laws distinguish between public roads, which are open to public use, and private roads, which are privately controlled. [17]

Maintenance is becoming an increasing problem in the United States. Between 1997 and 2018, the percentage of existing roads that are too bumpy to drive on compared to roads with decent surfaces increased from 10 to 21 percent. [18]


Transfagarasan called "the best road in the world" by Top Gear Transfagarasan.jpg
Transfăgărășan called "the best road in the world" by Top Gear
The Porta Rosa, a Greek street dating from the 3rd to 4th century BC in Velia, with a paved surface and gutters Greek street - III century BC - Porta Rosa - Velia - Italy.JPG
The Porta Rosa, a Greek street dating from the 3rd to 4th century BC in Velia, with a paved surface and gutters
A paved Roman road in Pompeii PompeiiStreet.jpg
A paved Roman road in Pompeii
Old tractor road over farmland, Ystad, Sweden Stora tvarvagen - Ystad 11sep2013.jpg
Old tractor road over farmland, Ystad, Sweden

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. [1] Some believe that some roads originated from following animal trails. [20] [21] The Icknield Way may examplify this type of road origination, where human and animal both selected the same natural line. [22] By about 10,000 BC human travelers used rough roads/pathways. [1]


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


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.
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
A beach road (Newcastle, NSW, Australia) Roads to Beaches of Newcastle, NSW in Australia.JPG
A beach road (Newcastle, NSW, Australia)
Rigid posts that can be arranged in a line to close a road or path to vehicles above a certain width
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
Road that avoids or "bypasses" a built-up area, town, or village
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.
Another name for cross slope or camber
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. [3]
Cat's eye
Reflective raised pavement marker used on roads
Sequence of tight serpentine curves (usually an S-shape curve or a bus stop)
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
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. [3]
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. [3]
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.
(literally "fork in the road") Type of intersection where a road splits
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.
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
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. [3]
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
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 [Louisiana English] or central nature strip (Australian English): Area that separates opposing lanes of traffic
(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. [3]
Mountain pass
A relatively low-level route through a range of mountains
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.
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
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. [36]
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. [37]
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
Part or all of the road is occupied for work or maintenance
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 35 m/s (126 km/h), waves with up to 350 m will excite motion sickness.
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 travelled in a clockwise direction. Also known as an island in parts of the UK.
Segregated 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. [37]
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
Pedestrians, ridden or herded animals, vehicles, bicycles, and other conveyances using any road for purposes of travel. [38]
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


Layers in the construction of a mortarless pavement: A.) Subgrade B.) Subbase C.) Base course D.) Paver base E.) Pavers F.) Fine-grained sand MortarlessPavement.jpg
Layers in the construction of a mortarless pavement: A.) Subgrade B.) Subbase C.) Base course D.) Paver base E.) Pavers F.) Fine-grained sand

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

Surveyor at work with a leveling instrument Us land survey officer.jpg
Surveyor at work with a leveling instrument
Asphalt layer and Hamm road roller Road building-Hungary-1.jpg
Asphalt layer and Hamm road roller
Sub-base layer composed of cement-based material being applied during construction of the M8 motorway in Ireland Motorway construction in Ireland.JPG
Sub-base layer composed of cement-based material being applied during construction of the M8 motorway in Ireland
Road construction in Myanmar. MyanmarRoadConstruction2.jpg
Road construction in Myanmar.
"Roadbed" (from the 'related terms' Bed (geology) & streambed), as well as the term "Road building" redirects here.

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, [39] :15 and may be required to meet standards set by law [40] or official guidelines. [41] 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. [42] [43]

After design, approval, planning, legal and environmental considerations have been addressed alignment of the road is set out by a surveyor. [33] The radii and gradient are designed and staked out to best suit the natural ground levels and minimize the amount of cut and fill. [41] :34 Great care is taken to preserve reference Benchmarks [41] :59

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. [41] :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 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. [41] :53–56

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. [41] :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). 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. [41] :68–69

Typical pavement strata for a heavily traveled road PavementStratum.JPG
Typical pavement strata for a heavily traveled road

General fill material should be free of organics, meet minimum California bearing ratio (CBR) results and have a low plasticity index. The lower fill generally comprises sand or a sand-rich mixture with fine gravel, which acts as an inhibitor to the growth of plants or other vegetable matter. The compacted fill also serves as lower-stratum drainage. Select second fill (sieved) should be composed of gravel, decomposed rock or broken rock below a specified particle size and be free of large lumps of clay. Sand clay fill may also be used. The roadbed must be "proof rolled" after each layer of fill is compacted. If a roller passes over an area without creating visible deformation or spring the section is deemed to comply. [41] :70–72

Geosynthetics such as geotextiles, geogrids and geocells are frequently used in the various pavement layers to improve road quality. These materials and methods are used in low-traffic private roadways as well as public roads and highways. [44] Geosynthetics perform four main functions in roads: separation, reinforcement, filtration and drainage; which increase the pavement performance, reduce construction costs and decrease maintenance. [45] [ self-published source ]

The completed roadway is finished by paving or left with a gravel or other natural surface. The type of road surface is dependent on economic factors and expected usage. Safety improvements such as traffic signs, crash barriers, raised pavement markers and other forms of road surface marking are installed.

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

When a single carriageway road is converted into dual carriageway by building a second separate carriageway alongside the first, it is usually referred to as duplication, [46] twinning or doubling. The original carriageway is changed from two-way to become one-way, while the new carriageway is one-way in the opposite direction. In the same way as converting railway lines from single track to double track, the new carriageway is not always constructed directly alongside the existing carriageway.


"Road works ahead" sign, typically used in Europe Baustelle.svg
"Road works ahead" sign, typically used in Europe

Like all structures, roads deteriorate over time. Deterioration is primarily due to accumulated damage from vehicles, however environmental effects such as frost heaves, thermal cracking and oxidation often contribute. [47] According to a series of experiments carried out in the late 1950s, called the AASHO Road Test, it was empirically determined that the effective damage done to the road is roughly proportional to the Fourth power of axle weight. [48] A typical tractor-trailer weighing 80,000 pounds (36.287 t) with 8,000 pounds (3.629 t) on the steer axle and 36,000 pounds (16.329 t) on both of the tandem axle groups is expected to do 7,800 times more damage than a passenger vehicle with 2,000 pounds (0.907 t) on each axle. Potholes on roads are caused by rain damage and vehicle braking or related construction works.

Line marking in rural India Making lines on the road.JPG
Line marking in rural India

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. [49] Roads can be and are designed for a variety of lives (8-, 15-, 30-, and 60-year designs). When pavement lasts longer than its intended life, it may have been overbuilt, and the original costs may have been too high. When a pavement fails before its intended design life, the owner may have excessive repair and rehabilitation costs. Some asphalt pavements are designed as perpetual pavements with an expected structural life in excess of 50 years. [50]

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. [51] Many concrete pavements built since the 1950s have significantly outlived their intended design lives. [52] Some roads like Chicago, Illinois's "Wacker Drive", a major two-level viaduct in the downtown area, are being rebuilt with a designed service life of 100 years. [53]

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 Profilometers. These measurements include road curvature, cross slope, asperity, roughness, rutting and texture. Software algorithms use this data to recommend maintenance or new construction.

Maintenance treatments for asphalt concrete generally include thin asphalt overlays, crack sealing, surface rejuvenating, fog sealingfo, micro milling or diamond grinding and surface treatments. Thin surfacing preserves, protects and improves the functional condition of the road while reducing the need for routing maintenance, leading to extended service life without increasing structural capacity. [54]

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. [55]

Failure to maintain roads properly can create significant costs to society, in a 2009 report released by the American Association of State Highway and Transportation Officials (US) about 50% of the roads in the US are in bad condition with urban areas worse. The report estimates that urban drivers pay an average of $746/year on vehicle repairs while the average US motorist pays about $335/year. In contrast, the average motorist pays about $171/year in road maintenance taxes (based on 600 gallons/year and $0.285/gallon tax).

Slab stabilization

Distress and serviceability loss on concrete roads can be caused by loss of support due to voids beneath the concrete pavement slabs. The voids usually occur near cracks or joints due to surface water infiltration. The most common causes of voids are pumping, consolidation, subgrade failure and bridge approach failure. Slab stabilization is a non-destructive method of solving this problem and is usually employed with other Concrete Pavement Restoration (CPR) methods including patching and diamond grinding. The technique restores support to concrete slabs by filing small voids that develop underneath the concrete slab at joints, cracks or the pavement edge.

The process consists of pumping a cementitious grout 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 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 utilized 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.


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. [56] [57]

Joint sealing

Also called joint and crack repair, this method's purpose is to minimize infiltration of surface water and incompressible material into the joint system. Joint sealants are also used to reduce dowel bar corrosion in Concrete Pavement Restoration (CPR) techniques. Successful resealing consists of old sealant removal, shaping and cleaning the reservoir, installing the backer rod and installing the sealant. Sawing, manual removal, plowing and cutting are methods used to remove the old sealant. Saws are used to shape the reservoir. When cleaning the reservoir, no dust, dirt or traces of old sealant should remain. Thus, it is recommended to water wash, sand-blast and then air blow to remove any sand, dirt or dust. The backer rod installation requires a double-wheeled, steel roller to insert the rod to the desired depth. After inserting the backer rod, the sealant is placed into the joint. There are various materials to choose for this method including hot pour bituminous liquid, silicone and preformed compression seals. [56] [58] [59] [60]

Safety considerations

Pedestrian crossing, line markings and street furniture. Wavy lines before pedestrian crossing.jpg
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 eyes or Botts dots, (bright reflectors that do not fade like paint). Botts dots are not used where it is icy in the winter, because frost and snowplows can break the glue that holds them to the road, although they can be embedded in short, shallow trenches carved in the roadway, as is done in the mountainous regions of California.

For major roads risk can be reduced by providing limited access from properties and local roads, grade separated junctions and median dividers between opposite-direction traffic to reduce the likelihood of head-on collisions.

The placement of energy attenuation devices (e.g. guardrails, wide grassy areas, sand barrels) is also common. Some road fixtures such as road signs and fire hydrants are designed to collapse on impact. Light poles are designed to break at the base rather than violently stop a car that hits them. Highway authorities may also remove larger trees from the immediate vicinity of the road. During heavy rains, if the elevation of the road surface isn't higher than the surrounding landscape, it may result in flooding. [61]

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

Road conditions

Snow causing bad road conditions Snowy road in Tieringen, Baden-Wurttemberg.jpg
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 pavement surface, potholes, 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". [62] It has further been specifically noted that "weather conditions and road conditions are interlinked as weather conditions affect the road conditions". [63] Specific aspects of road conditions can be of particular importance for particular purposes. For example, for autonomous vehicles such as self-driving cars, significant road conditions can include "shadowing and lighting changes, road surface texture changes, and road markings consisting of circular reflectors, dashed lines, and solid lines". [64]

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. [65]

Environmental performance

Air pollution along Pasadena Highway in Los Angeles Aab Pasadena Highway Los Angeles.jpg
Air pollution along Pasadena Highway in Los Angeles
A dual carriageway section of National Highway 8 connecting Delhi to Gurgaon DelhiFlyover EDITED.jpg
A dual carriageway section of National Highway 8 connecting Delhi to Gurgaon

Careful design and construction of a road can reduce any negative environmental impacts.

Road after rain Road in Rain.JPG
Road after rain

Water management systems can be used to reduce the effect of pollutants from roads. [66] [67] Rainwater and snowmelt running off of roads tends to pick up gasoline, motor oil, heavy metals, trash and other pollutants and result in water pollution. Road runoff is a major source of nickel, copper, zinc, cadmium, lead and polycyclic aromatic hydrocarbons (PAHs), which are created as combustion byproducts of gasoline and other fossil fuels. [68]

De-icing chemicals and sand can run off into roadsides, contaminate groundwater and pollute surface waters; [69] and road salts can be toxic to sensitive plants and animals. [70] 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? ] that design of roads can be conducted to influence and minimize noise generation. [71] Noise barriers can reduce noise pollution near built-up areas. Regulations can restrict the use of engine braking.

Motor vehicle emissions contribute air pollution. Concentrations of air pollutants and adverse respiratory health effects are greater near the road than at some distance away from the road. [72] Road dust kicked up by vehicles may trigger allergic reactions. [73] In addition, on-road transportation greenhouse gas emissions are the largest single cause of climate change, scientists say. [74]

The A22(T) with line markings near Summer Hill, East Sussex, England A22 northbound towards East Grinstead - - 68150.jpg
The A22(T) with line markings near Summer Hill, East Sussex, England
Road with guard rails in Kaluga Oblast, Russia Kaluga Region Trassa.jpg
Road with guard rails in Kaluga Oblast, Russia
Road with traffic signs in the outskirts of Bern, Switzerland Lutzelfluh-Goldbach3.jpg
Road with traffic signs in the outskirts of Bern, Switzerland
NH 73 going to Bangalore NH 73 from Bangalore.JPG
NH 73 going to Bangalore
Ontario Highway 401, a route with a collector / express setup 401 3x3x3x3.jpg
Ontario Highway 401, a route with a collector / express setup
The wide Coastal Road in the Philippines now called the Manila-Cavite Expressway Manila Cavite Expwy Tollgate.jpg
The wide Coastal Road in the Philippines now called the Manila-Cavite Expressway
Road in Jujuy Province, Argentina Ruta Nacional 9 en la Quebrada de Humahuaca, Jujuy (1).jpg
Road in Jujuy Province, Argentina


Australian drive on left sign Drive on left in australia.jpg
Australian drive on left sign

Right- and left-hand traffic

Traffic flows on the right or on the left side of the road depending on the country. [75] In countries where traffic flows on the right, traffic signs are mostly on the right side of the road, roundabouts and traffic circles go counter-clockwise/anti-clockwise, and pedestrians crossing a two-way road should watch out for traffic from the left first. [76] 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, [77] even though originally most traffic drove on the left worldwide. [78]


A city street in Mumbai, India with left-hand traffic Roadmumbaiindia.jpg
A city street in Mumbai, India with left-hand traffic

Transport economics is used to understand both the relationship between the transport system and the wider economy and the complex network effects when there are multiple paths and competing modes for both personal and freight (road/rail/air/ferry) and where Induced demand can result in increased on decreased transport levels when road provision is increased by building new roads or decreased (for example California State Route 480). Roads are generally built and maintained by the public sector using taxation although implementation may be through private contractors). [79] [80] or occasionally using road tolls. [81]

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: [82]

Society depends heavily on efficient roads. In the European Union (EU) 44% of all goods are moved by trucks over roads and 85% of all people are transported by cars, buses or coaches on roads. [83] The term was also commonly used to refer to roadsteads, waterways that lent themselves to use by shipping.

Construction costs

According to the New York State Thruway Authority, [84] some sample per-mile costs to construct multi-lane roads in several US northeastern states were:


The United States has the largest network of roads of any country with 4,050,717 miles (6,518,997 km) as of 2009. [85] The Republic of India has the second largest road system in the world with 4,689,842 kilometres (2,914,133 mi) of road (2013). [86] The People's Republic of China is third with 3,583,715 kilometres (2,226,817 mi) of road (2007). The Federative Republic of Brazil has the fourth largest road system in the world with 1,751,868 kilometres (1,088,560 mi) (2002). See List of countries by road network size. When looking only at expressways the National Trunk Highway System (NTHS) in China has a total length of 45,000 kilometres (28,000 mi) at the end of 2006, and 60,300 km at the end of 2008, second only to the United States with 90,000 kilometres (56,000 mi) in 2005. However, as of 2017 China has 130,000 km of Expressways. [87] [88]

Global connectivity

Eurasia, Africa, North America, South America, and Australia each have an extensive road network that connects most cities. The North and South American road networks are separated by the Darién Gap, the only interruption in the Pan-American Highway. Eurasia and Africa are connected by roads on the Sinai Peninsula. The European Peninsula 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 roads 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 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 113 mi (182 km) Overseas Highway connecting many of the Florida Keys with the continental United States.

Even on mainlands, some settlements have no roads connecting with the primary continental network, due to natural obstacles like mountains or wetlands, remoteness, or general expense. 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. [89] Due to steepness, mud, snow, or fords, roads can sometimes be passable only to four-wheel drive vehicles, those with snow chains or snow tires, or those capable of deep wading or amphibious operation.

Cities on the mainland of continents which do not have road access include:

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

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

In polar areas, disconnected settlements are often more easily reached by snowmobile or dogsled in cold weather, which can produce sea ice 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 to Murmansk in Russia, and many roads in Scandinavia (though due to fjords water transport is sometimes faster). Large areas of Alaska, Canada, Greenland, and Siberia are sparsely connected. For example, all 25 communities of Nunavut are disconnected from each other and the main North American road network. [90]

Road transport of people and cargo by may also be obstructed by border controls and travel restrictions. For example, travel from other parts of Asia to South Korea would require passage through the hostile country of North Korea. Moving between most countries in Africa and Eurasia would require passing through Egypt and Israel, which is a politically sensitive area.

Some places are intentionally car-free, and roads (if present) might be used by bicycles or pedestrians.

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

See also

Related Research Articles

Traffic Road users travelling by foot or vehicle

Traffic on roads consists of road users including pedestrians, ridden or herded animals, vehicles, streetcars, buses and other conveyances, either singly or together, while using the public way for purposes of travel. Traffic laws are the laws which govern traffic and regulate vehicles, while rules of the road are both the laws and the informal rules that may have developed over time to facilitate the orderly and timely flow of traffic.

Road transport collective term for all forms of transport which takes place on roads, or (ground) surface, exept railroads

Road transport or road transportation is a type of transport by using roads. Transport on roads can be roughly grouped into the transportation of goods and transportation of people. In many countries licensing requirements and safety regulations ensure a separation of the two industries. Movement along roads may be by bike or automobile, truck, or by animal such as horse or oxen. Standard networks of roads were adopted by Romans, Persians, Aztec, and other early empires, and may be regarded as a feature of empires. Cargo may be transported by trucking companies, while passengers may be transported via mass transit. Commonly defined features of modern roads include defined lanes and signage. Various classes of road exist, from two-lane local roads with at-grade intersections to controlled-access highways with all cross traffic grade-separated.

Sidewalk pedestrian path along the side of a road

A sidewalk or pavement, also known as a footpath or footway, is a path along the side of a road. It is often constructed of concrete or cement, though occasionally asphalt, and is designed for pedestrians. A sidewalk may accommodate moderate changes in grade (height) and is normally separated from the vehicular section by a curb. There may also be a median strip or road verge either between the sidewalk and the roadway or between the sidewalk and the boundary.

Roundabout Traffic intersection

A roundabout is a type of circular intersection or junction in which road traffic is permitted to flow in one direction around a central island, and priority is typically given to traffic already in the junction.

Pedestrian crossing Point on a road at which some means are employed to assist pedestrians wishing to cross

A pedestrian crossing or crosswalk is a place designated for pedestrians to cross a road, street or avenue. Pelican crosswalks are designed to keep pedestrians together where they can be seen by motorists, and where they can cross most safely across the flow of vehicular traffic.

Street A public thoroughfare in a built environment

A street is a public thoroughfare in a built environment. It is a public parcel of land adjoining buildings in an urban context, on which people may freely assemble, interact, and move about. A street can be as simple as a level patch of dirt, but is more often paved with a hard, durable surface such as tarmac, concrete, cobblestone or brick. Portions may also be smoothed with asphalt, embedded with rails, or otherwise prepared to accommodate non-pedestrian traffic.

Highway engineering branch of civil engineering focused on roads, bridges, and tunnels

Highway engineering is an engineering discipline branching from civil engineering that involves the planning, design, construction, operation, and maintenance of roads, bridges, and tunnels to ensure safe and effective transportation of people and goods. Highway engineering became prominent towards the latter half of the 20th Century after World War II. Standards of highway engineering are continuously being improved. Highway engineers must take into account future traffic flows, design of highway intersections/interchanges, geometric alignment and design, highway pavement materials and design, structural design of pavement thickness, and pavement maintenance.

Road surface road covered with durable surface material

A road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past, gravel road surfaces, cobblestone and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete laid on a compacted base course. Asphalt mixtures have been used in pavement construction since the beginning of the twentieth century. These roads are of two types metalled roads and unmetalled roads. The metalled roadways are made to sustain vehicular load, so these type of roads are usually made in the places where a lot of vehicles cross daily. Unmetalled roads are the roads which are rough and are also known as gravel roads. These roads are not metalled and so they can't sustain a lot of weight. So that is the reason that these roads usually have bumps. Road surfaces are frequently marked to guide traffic. Today, permeable paving methods are beginning to be used for low-impact roadways and walkways. Pavements are crucial to countries such as US and Canada, which heavily depend on road transportation. Therefore, research projects such as Long-Term Pavement Performance are launched to optimize the life-cycle of different road surfaces.

Road traffic safety Methods and measures for reducing the risk of death and injury on roads

Road traffic safety refers to the methods and measures used to prevent road users from being killed or seriously injured. Typical road users include pedestrians, cyclists, motorists, vehicle passengers, horse riders, and passengers of on-road public transport.

Asphalt concrete composite material commonly used as a road surface

Asphalt concrete is a composite material commonly used to surface roads, parking lots, airports, as well as the core of embankment dams. Asphalt mixtures have been used in pavement construction since the beginning of the twentieth century. It consists of mineral aggregate bound together with asphalt, laid in layers, and compacted. The process was refined and enhanced by Belgian inventor and U.S. immigrant Edward De Smedt.

Permeable paving roads built with water pervious materials to limit surface runoff

Permeable paving is a method of paving vehicle and pedestrian pathways to enable infiltration of stormwater runoff. Permeable pavement surfaces typically include pervious concrete, porous asphalt, paving stones and interlocking pavers. Unlike traditional impervious paving materials, permeable paving systems allow stormwater to percolate and infiltrate through the pavement and into the aggregate layers and/or soil below. In addition to reducing surface runoff, permeable paving systems can trap suspended solids, thereby filtering pollutants from stormwater. The goal is to control stormwater at the source, reduce runoff and improve water quality by filtering pollutants in the subsurface layers.

Cobblestone natural building material based on cobble-sized stones, and is used for pavement roads, streets, and buildings

Cobblestone is a natural building material based on cobble-sized stones, and is used for pavement roads, streets, and buildings.

Lane division of the carriageway within a road designated to be used by a single line of vehicles

In the context of traffic control, a lane is part of a roadway (carriageway) that is designated to be used by a single line of vehicles, to control and guide drivers and reduce traffic conflicts. Most public roads (highways) have at least two lanes, one for traffic in each direction, separated by lane markings. On multilane roadways and busier two-lane roads, lanes are designated with road surface markings. Major highways often have two multi-lane roadways separated by a median.

Rumble strip road safety feature

Rumble strips, also known as sleeper lines, alert strips, audible lines, sleepy bumps, wake up calls, growlers, drift lines, and drunk bumps, are a road safety feature to alert inattentive drivers of potential danger, by causing a tactile vibration and audible rumbling transmitted through the wheels into the vehicle interior. A rumble strip is applied along the direction of travel following an edgeline or centerline, to alert drivers when they drift from their lane. Rumble strips may also be installed in a series across the direction of travel, to warn drivers of a stop or slowdown ahead, or of an approaching danger spot.

Raised pavement marker safety device

A raised pavement marker is a safety device used on roads. These devices are usually made with plastic, ceramic, thermoplastic paint, glass or occasionally metal, and come in a variety of shapes and colors. Raised reflective markers, such as plastic, ceramic, metal ones, include a lens or sheeting that enhances their visibility by retroreflecting automotive headlights, while glass road studs gather automotive headlights with a dome shape and reflect the lights with a reflective layer within. Some other names for specific types of raised pavement markers include convex vibration lines, Botts' dots, delineators, cat's eyes, road studs, or road turtles. Sometimes they are simply referred to as "reflectors".

Road surface marking Any kind of device or material used on a road surface to convey official information

Road surface marking is any kind of device or material that is used on a road surface in order to convey official information; they are commonly placed with road marking machines. They can also be applied in other facilities used by vehicles to mark parking spaces or designate areas for other uses.

Curb edge where a sidewalk meets a road

A curb, or kerb, is the edge where a raised sidewalk or road median/central reservation meets a street or other roadway.

Rut (roads) depression or groove worn into a road or path

A rut is a depression or groove worn into a road or path by the travel of wheels or skis. Ruts can be formed by wear, as from studded snow tires common in cold climate areas, or they can form through the deformation of the asphalt concrete pavement or subbase material. The main reason is heavy loaded truck acts more pressure than assumed during the construction of roads. These heavy loaded trucks will imprint the tire impression on roads causing ruts.

Diamond grinding is a pavement preservation technique that corrects a variety of surface imperfections on both concrete and asphalt pavements. Most often utilized on concrete pavement, diamond grinding is typically performed in conjunction with other concrete pavement preservation (CPP) techniques such as road slab stabilization, full- and partial-depth repair, dowel bar retrofit, cross stitching longitudinal cracks or joints and joint and crack resealing. Diamond grinding restores rideability by removing surface irregularities caused during construction or through repeated traffic loading over time. The immediate effect of diamond grinding is a significant improvement in the smoothness of a pavement. Another important effect of diamond grinding is the considerable increase in surface macrotexture and consequent improvement in skid resistance, noise reduction and safety.

Glossary of road transport terms Wikimedia list article

Terminology related to road transport—the transport of passengers or goods on paved routes between places—is diverse, with variation between dialects of English. There may also be regional differences within a single country, and some terms differ based on the side of the road traffic drives on. This glossary is an alphabetical listing of road transport terms.


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