A road is an identifiable route, way or path between places. Roads are typically smoothed, paved, or otherwise prepared to allow easy travel; though they need not be, and historically many roads were simply recognizable routes without any formal construction or maintenance.
The term was also commonly used to refer to roadsteads, waterways that lent themselves to use by shipping. Notable examples being Hampton Roads, in Virginia, the seaway Barry Roads in the Bristol Channel and Castle Roads, in Bermuda (also formerly in Virginia).
For purposes of international comparison, the OECD has defined a road to be:
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 United States has the largest network of roadways of any country with 6,430,366 kilometres (3,995,644 mi) (2005). The Republic of India has the second largest road system in the world with 3,383,344 kilometres (2,102,312 mi) (2002). People's Republic of China is third with 1,870,661 kilometres (1,162,375 mi) of roadway (2004).. As of 2007, China had a total road length of 3,583,700 kilometres (2,226,800 mi)
When looking only at expressways the National Trunk Highway System (NTHS) in People's Republic of 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.
Historical road construction
Main article: History of road transportThat 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.
- Stone paved streets are found in the city of Ur in the Middle East dating back to 4000 BC
- Corduroy roads (log roads) are found dating to 4,000 BC in Glastonbury, England
- The timber trackway; Sweet 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 has been claimed to be the oldest road in the world.
- Brick paved streets were used in India as early as 3000 BC
- In 500 BC, Darius I the Great started an extensive road system for Persia (Iran), including the famous Royal Road which was one of the finest highways of its time. The road remained in use after Roman times.
- 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 700s 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.
- In the 1600s road construction and maintenance in Britain was traditionally done on a local parish basis. 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 of engineered roads. The Rebecca Riots in Carmarthenshire and Rhayader from 1839 to 1844 contributed to a Royal Commission leading to the demise of the system in 1844.
Road transport economics
Main article: Transport economicsTransport economics is a branch of economics that deals with the allocation of resources within the transport sector and has strong linkages with civil engineering. Transport economics differs from some other branches of economics in that the assumption of a spaceless, instantaneous economy does not hold. People and goods flow over networks at certain speeds. Demands peak. Advanced ticket purchase is often induced by lower fares. The networks themselves may or may not be competitive. A single trip (the final good from the point-of-view of the consumer) may require bundling the services provided by several firms, agencies and modes.
Although transport systems follow the same supply and demand theory as other industries, the complications of network effects and choices between non-similar goods (e.g. car and bus travel) make estimating the demand for transportation facilities difficult. The development of models to estimate the likely choices between the non-similar goods involved in transport decisions "discrete choice" models led to the development of the important branch of econometrics, and a Nobel Prize for Daniel McFadden.
In transport, demand can be measured in numbers of journeys made or in total distance traveled across all journeys (e.g. passenger-kilometres for public transport or vehicle-kilometres of travel (VKT) for private transport). Supply is considered to be a measure of capacity. The price of the good (travel) is measured using the generalised cost of travel, which includes both money and time expenditure. The effect of increases in supply (capacity) are of particular interest in transport economics (see induced demand), as the potential environmental consequences are significant.
Road building and maintenance is an area of economic activity that remains dominated by the public sector (though often through private contractors). Roads (except those on private property that are not accessible to the general public) are typically paid for by taxes (often raised through levies on fuel), though some public roads, especially freeways are funded by tolls.
Environmental aspects
Air pollution
Motor vehicles operating on roads contribute emissions, particularly for congested city street conditions and other low speed circumstances. Of particular concern are particulate emissions from diesel engines. 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
Urban runoff from roads and other impervious surfaces is a major source of water pollution. 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. Road salts (primarily chlorides of sodium, calcium or magnesium) can be toxic to sensitive plants and animals. Sand can alter stream bed environments, causing stress for the plants and animals that live there.
Noise pollution
Mot
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