Road

in Florence, Italy]] with hairpin turns in the Swiss Alps, Switzerland]] A road is an identifiable thoroughfare, route, way or path between two places which may or may not be available for use by the public; public roads, especially major roads connecting significant destinations are termed highways. Modern roads are normally smoothed, paved, or otherwise prepared to allow easy travel although historically many roads were simply recognizable routes without any formal construction or maintenance. 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. Economics and society depend heavily on efficient roads. In the European Union (EU) 44% of all goods are moved by trucks over roads and 85% of all persons are transported by cars, buses or coaches on roads. The term was also commonly used to refer to roadsteads, waterways that lent themselves to use by shipping.

The United States has the largest network of roadways of any country with (2005). The People's Republic of China is second with of roadway (2007) See List of countries by road network size. The Republic of India has the third largest road system in the world with (2002). When looking only at expressways the National Trunk Highway System (NTHS) in People's Republic of China has a total length of at the end of 2006, and 60,300 km at the end of 2008, second only to the United States with in 2005.

Historical road construction

street dating from the 3rd to 4th century BC in Velia, Italy with a paved surface and gutters.]] , Italy]] That the first pathways were the trails made by animals has not been universally accepted, arguing that animals do not follow constant paths. Others believe that some roads originated from following animal trails. The Icknield Way is given as an example of this type of road origination, where man and animal both selected the same natural line. By about 10,000 BC, rough pathways were used by human travelers. The road remained in use after Roman times. In ancient times, transport by river was far easier and faster than transport by road,

* From about 312 BC, the Roman Empire built straight

* In the 8th century AD, many roads were built throughout the Arab Empire. The most sophisticated roads were those of the Baghdad, Iraq, which were paved with tar in the 8th century. 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 required local parishes to maintain their roads. which also coincided with the development of the UK railway system.

Construction

.]] in Ireland.]] Road construction requires the creation of a continuous right-of-way, overcoming geographic obstacles and having grades low enough to permit vehicle or foot travel. ^(pg15) 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., 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.

Maintenance

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. 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 4th power of axle weight. A typical tractor-trailer weighing 80,000 pounds (36.287 t) with 8,000 pounds (3.6287 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.

Pavements are designed for an expected service life or design life. In some UK countries 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. 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. Many concrete pavements built since the 1950s have significantly outlived their intended design lives. Some roads like Chicago, Illinois's "Wacker Drive", a major two-level viaduct in downtown area are being rebuilt with a designed service life of 100 years.

Virtually all roads require some form of maintenance before they come to the end of their service life. Pro-active agencies continually monitor road conditions and apply preventive maintenance treatments as needed to prolong the lifespan of their roads. Technically advanced agencies monitior the road network surface condition with sophisticated equipment such as laser/inertial Profilometers. These measurements include road curvature, cross slope, unevenness, roughness, rutting and texture (roads). This data is fed into a pavement management system, which recommends the best maintenance or construction treatment to correct the damage that has occurred.

Maintenance treatments for asphalt concrete generally include crack sealing, surface rejuvenating, fog sealing, micro-milling 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.

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 (USA) about 50% of the roads in the USA 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 cementitous 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.

Another testing method is ground penetrating radar. It pulses electromagnetic wave technology into the pavement and then ceases the transmission during which the transmitter-receiver detects signals that are deflected from the pavement. Yet another method is the epoxy/core test, which confirms void presence by visual and mechanical methods. It consists of drilling a 25 to 50 millimeter hole through the pavement and into the sub-base with a dry-bit roto-hammer. Next, a two-part epoxy is poured into the hole that is dyed for visual clarity. Once the epoxy is hardened, the technicians drill through the hole. If a void is present, the epoxy will stick to the core and provide physical evidence.

Common stabilization materials are 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 should 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 that is capable of sealing a 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.

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.

Road safety

, line markings and street furniture.]] A report published by the World Health Organization in 2004 estimated that some 1.2m people were killed and 50m injured on the roads around the world each year and was the leading cause of death among children 10 – 19 years of age. Careful design and construction of roads can 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 all protect pedestrians and cyclists.

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 likelihood of head-on collisions. The placement of energy attenuation devices (e.g. guardrails, wide grassy areas, sand barrels). 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 have also removed trees in the vicinity of roads although the idea of "dangerous trees" has attracted a certain amount of skepticism. 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.

Environment

, United States]] Road have both local and wider environmental effects and can be mitigated to varying degrees during the design, construction and maintenance process.

Motor vehicle emissionss 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. Road dust kicked up by vehicles may trigger allergic reactions. Sand applied to icy roads can be ground up by traffic into fine particulates and contribute to air pollution.

Water pollution from roads can also be a problem with rainwater and snowmelt running off of roads tends to pick up gasoline, motor oil, heavy metals, trash and other pollutants. 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. De-icing chemicals and sand can run off into roadsides, contaminate groundwater and pollute surface waters; and road salts can be toxic to sensitive plants and animals. Sand can alter stream bed environments, causing stress for the plants and animals that live there. Water management systems can be used to reduce the effect of these pollutants.

Noise pollution from motor vehicles increases with speed, near intersections and on uphill sections. Noise mitigation strategies exist to reduce sound levels at nearby sensitive receptors. The idea that road design could be influenced by acoustical engineering considerations first arose about 1973.

Financing

, 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). or occasionally using road tolls.

Construction costs

According to www.nysthruway.gov, some typical costs to construct roads in several USA states include: CONSTRUCTION COST Expressway Section Per-Mile Cost Connecticut Turnpike $3,449,000 New Jersey Turnpike $2,200,000 Pennsylvania Turnpike (Delaware Extension) $1,970,000 Northern Indiana Toll Road $1,790,000 Garden State Parkway $1,720,000 Massachusetts Turnpike $1,600,000 Thruway, New York to Pennsylvania Line $1,547,000 Ohio Turnpike $1,352,000 Pennsylvania Turnpike (early construction) $736,000

Regulation

Right- and left-hand traffic

Traffic flows on the right or on the left side of the road depending on the country. In countries where traffic flows on the right, traffic signs are mostly on the right side of the road, 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. 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 roadway distances, about 28% drive on the left, and 72% on the right, even though originally most traffic drove on the left worldwide.

Terminology

with line markings near Summer Hill, East Sussex, England, United Kingdom]] s in Kaluga Oblast, Russia]] s in the outskirts of Bern, Switzerland]] , a route with a collector / express setup.]]

Alignment (road) - horizontal and vertical curvature of a road.

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.

All-weather road - Unpaved road that is constructed of a material that does not create mud during rainfall.

:* Banked turn :* Camber - the curvature of the road surface that encourages surface water to flow freely from the carriageway, or on bends angling of the surface to lean traffic 'into the bend' reducing the chance of a skid. :* Cant - superelevation :* Cross slope :* Grade - longitudinal slope

Belisha Beacon - an orange globe, lit at night, used to highlight a pedestrian crossing.

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 which is used mainly as footpaths and bridleways

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

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) in a roadway

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 a concrete, in the U.S. 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

Curb - Edge where a raised pavement/sidewalk/footpath, road median, or road shoulder meets an unraised street or other roadway.

Curb extension - (or 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.

Farm-to-market road - a state road or county road which serves to connect rural or agricultural areas to market towns.

Fork - (literally "fork in the road") Type of intersection where a road splits

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, similar to a Byway

Guard rail - Prevents vehicles from veering off the road into oncoming traffic, crashing against solid objects or falling from a road

Gutter - UK a drainage channel between the main carriageway and the edge of the road.

Interstate Highway System - United States System of Interstate and Defense Highways

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 which have come loose.

Median - On divided roads, including expressways, motorways, or autobahns, 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) is the area which separates opposing lanes of traffic

Mountain pass - Lower point that allows easier access through a range of mountains

Milestone - One of a series of numbered markers placed along a road 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 at which some means are employed to assist pedestrians wishing to 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

Public space - Place where anyone has a right to come without being excluded because of economic or social conditions

Ranch road - U.S. road which serves to connect rural and agricultural areas to market towns

Road number - Often assigned to a stretch of public roadway. The number chosen is often dependent on the type of road, with numbers differentiating between interstates, motorways, arterial thoroughfares, and so forth

Road-traffic safety - Process to reduce the harm (deaths, injuries, and property damage) resulting from crashes of road vehicles traveling on public roads

Roadworks - Part or all of the road has to be occupied for work or maintenance relating to the road

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 35 m/s (126 km/h), waves with up to 350 m will excite motion sickness.

Roundabout UK 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 countrys where traffic drives on the left the roundabout is travelled in a clockwise direction. Also known as an island in parts of the UK.

Shoulder - A clear, level area beside the driving lane(s). It helps support the roadway, helps drain the pavement, provides room for bicyclists and, in areas without sidewalks, pedestrians, allows disabled to get out of the road; a hard shoulder is paved, a soft shoulder is unpaved.

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

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 which aim to slow down or reduce traffic, thereby improving safety for pedestrians and bicyclists as well as improving the environment for residents

Traffic island - UK a small raised area used to help define the traffic flow, and 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, robot or semaphore, is a signaling device positioned at a road intersection, pedestrian crossing, or other location in order to assign right of way to different approaches to an intersection

Zebra Crossing - UK a pedestrian crossing marked by black and white stripes on the carriageway.

See also

References

External links

The Post-Roads of Europe 1781 Map

National Alliance Against Tolls

The Roadex project

The Greenroads Rating System

Category:Types of roads