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Road
The world's oldest known paved road was constructed in Egypt some time between 2600 and 2200 BC, yet the concept of a road predates stone and mortar by millennia. Before the first stone was laid, human travelers used rough pathways by about 10,000 BC, often following trails made by animals. While the assertion that the first pathways were simply animal trails has not been universally accepted, some believe that roads originated from following these animal routes. The Icknield Way may exemplify this type of road origination, where both human and animal selected the same natural line. Even older than the Egyptian paved roads is the Corduroy road found in Glastonbury, England, dating to 4000 BC. These log roads were an early engineering solution to muddy terrain, using timber to create a stable surface for travel. Another contender for the title of the oldest road is the Sweet Track, a timber track causeway in England built in winter 3807 BC or spring 3806 BC. Tree-ring dating enabled very precise dating for this structure, which was claimed to be the oldest road in the world until the 2009 discovery of a 6,000-year-old trackway in Plumstead, London. These ancient routes were not merely dirt paths but engineered solutions that required significant labor and planning to overcome the natural landscape.
As civilizations grew, so did the complexity of their road systems. In 500 BC, Darius I the Great started an extensive road system for the Achaemenid Empire, including the Royal Road. This highway was one of the finest of its time, connecting Sardis, the westernmost major city of the empire, to Susa. The road remained in use after Roman times and reached as far east as Bactria and India. The Roman Empire later built straight strong stone roads throughout Europe and North Africa, starting from about 312 BC, in support of its military campaigns. At its peak, the Roman Empire was connected by 29 major roads moving out from Rome, covering 78,000 kilometers or 52,964 Roman miles of paved roads. These roads were not just for trade but were vital arteries for the movement of armies and the consolidation of imperial power. In the 8th century AD, many roads were built throughout the Arab Empire, with the most sophisticated roads being 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, marking an early use of bitumen in road construction.
The history of roads is also a history of the struggle between public access and private control. 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, prompting the establishment of the first turnpike trusts around 1706 to build good roads and collect tolls from passing vehicles. Eventually, there were approximately 1,100 trusts in Britain, and some of these engineered roads became the backbone of the nation's transport network. 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. This shift marked a turning point where the state began to take a more active role in infrastructure, moving away from the fragmented turnpike model that had dominated for over a century.
Common questions
What is the oldest known paved road in the world and when was it built?
The world's oldest known paved road was constructed in Egypt between 2600 and 2200 BC. This structure predates the concept of stone and mortar by millennia, yet human travelers used rough pathways by about 10,000 BC.
When was the Sweet Track built and where is it located?
The Sweet Track is a timber track causeway in England built in winter 3807 BC or spring 3806 BC. Tree-ring dating enabled very precise dating for this structure, which was claimed to be the oldest road in the world until the 2009 discovery of a 6,000-year-old trackway in Plumstead, London.
Who started the Royal Road and when did construction begin?
Darius I the Great started an extensive road system for the Achaemenid Empire in 500 BC. This highway connected Sardis, the westernmost major city of the empire, to Susa and remained in use after Roman times.
How much does it cost the average American motorist to drive on rough roads annually?
According to a May 2009 report by the American Association of State Highway and Transportation Officials and TRIP, 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.
Which country has the largest network of roads in the world as of 2009?
The United States has the largest network of roads of any country with as of 2009. The Republic of India has the second-largest road system globally with of road in 2013, and the People's Republic of China is third with of road in 2007.
What is the difference between a road and a street according to the Organization for Economic Co-operation and Development?
The Organization for Economic Co-operation and Development defines a road as a line of communication 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. Roads differ from streets, whose primary use is local access.
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. 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. A variety of road building equipment is employed in road building, from heavy excavators to specialized pavers. After design, approval, planning, legal, and environmental considerations have been addressed, the 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, ensuring that the road follows the intended path with precision.
The layers of a modern road are a testament to engineering ingenuity. The completed roadway is finished by paving or left with a gravel or other natural surface, depending 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. Geosynthetics such as geotextiles, geogrids, and geocells are frequently used in the various pavement layers to improve road quality. These materials perform four main functions in roads: separation, reinforcement, filtration, and drainage, which increase pavement performance, reduce construction costs, and decrease maintenance. 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. General fill material should be free of organics, meet minimum California bearing ratio 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 Autostrada dei Laghi, or Lakes Motorway, in Italy, stands as a monumental achievement in road history. Devised by Piero Puricelli and inaugurated in 1924, it was the first controlled-access highway built in the world, connecting Milan to Lake Como and Lake Maggiore. This motorway, called autostrada, contained only one lane in each direction and no interchanges, yet it set the standard for future highway construction. The layers in the construction of a mortarless pavement include the subgrade, subbase, base course, paver base, pavers, and fine-grained sand. Each layer serves a specific purpose, from supporting the weight of traffic to providing drainage and stability. The process of building a road is a complex dance of geology, chemistry, and physics, requiring the coordination of thousands of workers and machines to create a surface that can withstand the relentless pressure of modern life.
The Cost Of A Broken Surface
Like all structures, roads deteriorate over time, and the cost of this deterioration is borne by the public. Deterioration is primarily due to environmental effects such as frost heaves, thermal cracking, and oxidation, however accumulated damage from vehicles also contributes. 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. A typical tractor-trailer weighing 80,000 pounds with 8,000 pounds on the steer axle and 36,000 pounds on both of the tandem axle groups is expected to do 7,800 times more damage than a passenger vehicle with 2,000 pounds on each axle. This mathematical reality means that heavy trucks are the primary destroyers of road surfaces, necessitating a constant cycle of repair and maintenance.
Potholes on roads are caused by rain damage and vehicle braking or related construction work, creating hazards for drivers and increasing vehicle operating costs. According to a May 2009 report by the American Association of State Highway and Transportation Officials and TRIP, 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. In contrast, the average motorist pays about $171 a year in road maintenance taxes, highlighting a significant disparity between the cost of poor roads and the revenue generated to fix them. A 2009 report estimated that about 50% of the roads in the US are in bad condition, with urban areas being worse.
Maintenance treatments for asphalt concrete generally include thin asphalt overlays, crack sealing, surface rejuvenating, fog sealing, micro milling, or diamond grinding. Waterblasting can also be part of the maintenance, increasing the friction of the surface through a slight removal of the top bitumen layer as well as brightening the surface, which leads to less wear through temperature in the bottom layers of the surface. 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. 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. Some roads like Chicago's Wacker Drive, a major two-level roadway in the downtown area, are being rebuilt with a designed service life of 100 years, a testament to the evolving standards of road engineering.
The Safety And The Environment
Careful design and construction of roads can increase road traffic safety and reduce the harm 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. 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, such as guardrails, wide grassy areas, and sand barrels, is also common. Some road fixtures such as road signs and fire hydrants are designed to collapse on impact, while light poles are designed to break at the base rather than violently stop a car that hits them.
Roads are also a chief source of noise pollution and air pollution. In the early 1970s, it was recognized that the design of roads can be conducted to influence and minimize noise generation. Noise barriers can reduce noise pollution near built-up areas, and regulations can restrict the use of engine braking. Motor vehicle emissions contribute air pollution, and 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. In addition, on-road transportation greenhouse gas emissions are the largest single cause of climate change, scientists say. Water management systems can be used to reduce the effect of pollutants from roads. Rainwater and snowmelt running off of roads tend 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, 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.
The Global Network And The Gaps
The United States has the largest network of roads of any country with as of 2009, followed by the Republic of India with the second-largest road system globally with of road in 2013. The People's Republic of China is third with of road in 2007, and the Federative Republic of Brazil has the fourth-largest road system in the world with in 2002. When looking only at expressways, the National Trunk Highway System in 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. However, as of 2017, China has 130,000 km of Expressways. 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. 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, even though originally most traffic drove on the left worldwide. Even on mainlands, some settlements have no roads connecting with the primary continental network, due to natural obstacles like mountains or wetlands, or high cost compared to the population served. Unpaved roads or lack of roads are more common in developing countries, and these can become impassable in wet conditions. As of 2014, only 43% of rural Africans have access to an all-season road. For long-distance trips, passengers usually travel by air and rent a car upon arrival, or vehicles and cargo can be shipped to many disconnected settlements by boat, or air transport at much greater expense.
The Economics Of The Asphalt
Transport economics is used to understand both the relationship between the transport system and the wider economy and the complex effects of the road network structure when there are multiple paths and competing modes for both personal and freight. Roads are generally built and maintained by the public sector using taxation, although implementation may be through private contractors, or occasionally using road tolls. 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: design/build, design/build/operate/maintain, design/build/finance/operate, and build/own/operate. Society depends heavily on efficient roads. In the European Union, 44% of all goods are moved by trucks over roads and 85% of all people 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.
Construction costs vary significantly depending on the location and complexity of the project. According to the New York State Thruway Authority, some sample per-mile costs to construct multi-lane roads in several US northeastern states were: Connecticut Turnpike at $3,449,000 per mile, New Jersey Turnpike at $2,200,000 per mile, and Pennsylvania Turnpike at $1,970,000 per mile. The Northern Indiana Toll Road cost $1,790,000 per mile, while the Garden State Parkway cost $1,720,000 per mile. The Massachusetts Turnpike cost $1,600,000 per mile, and the Thruway, New York to Pennsylvania Line cost $1,547,000 per mile. The Ohio Turnpike cost $1,352,000 per mile, and the early construction of the Pennsylvania Turnpike cost $736,000 per mile. These figures illustrate the immense financial investment required to build and maintain the road networks that underpin modern civilization. The cost of roads is not just a matter of construction but also of the ongoing maintenance and the economic impact of poor road conditions on the vehicles and the people who use them.
The Future Of The Road
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. 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. 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. The future of roads will likely involve a balance between expanding connectivity and preserving the unique character of the places they pass through.
The words road and street are commonly considered to be interchangeable, but the distinction is important in urban design. Roads differ from streets, whose primary use is local access. Roads also differ from stroads, which combine the features of streets and roads. There are many types of roads, including parkways, avenues, controlled-access highways, tollways, highways, local roads, public roads, and private roads. The primary features of roads include lanes, sidewalks, roadways, medians, shoulders, verges, bike paths, and shared-use paths. The Organization for Economic Co-operation and Development defines a road as a line of communication 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. This includes bridges, tunnels, supporting structures, junctions, crossings, interchanges, and toll roads, but not cycle paths.
In the United Kingdom, the Highway Code details rules for road users, but there is some ambiguity between the
The Definition And The Law
terms highway and road. For the purposes of the English law, the 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. 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, river beds, road shoulders, wharves, and bridges are included. However, the definition of a road for insurance purposes may be restricted to reduce risk.