Road
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. This definition includes bridges, tunnels, supporting structures, junctions, crossings, interchanges, and toll roads but excludes cycle paths. Eurostat, ITF and UNECE Glossary for Transport Statistics Illustrated offers a similar view describing it as a line of communication open to public traffic primarily for road motor vehicles. They include paved roads and gravel roads while excluding dedicated cycle lanes. The 1968 Vienna Convention on Road Traffic defines the term as the entire surface of any way or street open to public traffic. Australia's National Transport Commission Regulations 2006 define it as an area open to or used by the public developed for driving or riding motor vehicles. New Zealand law takes a broad approach including beaches, car parks, yards, river beds, wharves, and bridges in its statutory definition. In the United Kingdom the Highways Act 1980 covers England and Wales stating that a road is any length of highway or other road to which the public has access. It includes footpaths, bridleways, cycle tracks, driveways on private land, and many car parks. A 1984 ruling clarified that the presence or absence of a made road has nothing to do with the distinction between highways and roads. The American Association of State Highway and Transportation Officials notes that laws distinguish between public roads open to all and private roads under private control.
The world's oldest known paved road was constructed in Egypt some time between 2600 and 2200 BC. Corduroy roads dating back to 4000 BC exist in Glastonbury, England. The Sweet Track timber trackway in Northern Europe was built in winter 3807 BC or spring 3806 BC according to tree-ring dating. Darius I the Great started an extensive road system for the Achaemenid Empire around 500 BC connecting Sardis to Susa. This Royal Road remained in use after Roman times and reached as far east as Bactria and India. From about 312 BC the Roman Empire built straight strong stone roads throughout Europe and North Africa to support military campaigns. At its peak the Roman Empire connected 78,000 kilometers or 52,964 Roman miles of paved roads via 29 major routes from Rome. In the 8th century AD many roads were built throughout the Arab Empire with the most sophisticated ones in Baghdad paved with tar derived from petroleum. The Highways Act 1555 in Britain transferred responsibility for maintaining roads from government to local parishes resulting in a poor state of infrastructure. The first turnpike trusts were established around 1706 to build good roads and collect tolls from passing vehicles. Approximately 1,100 trusts existed before the Rebecca Riots in Carmarthenshire and Rhayader led to their demise in 1844. The Autostrada dei Laghi in Italy was the first controlled-access highway ever built in the world inaugurated in 1924 by Piero Puricelli.
Road construction requires creating an engineered continuous right-of-way overcoming geographic obstacles with grades low enough for vehicle travel. The process begins with removing earth and rock by digging or blasting followed by constructing embankments bridges and tunnels. Surveyors set out alignment after design approval planning legal and environmental considerations are addressed. Radii and gradients are designed to suit natural ground levels minimizing cut and fill operations. A borrow pit source for obtaining fill gravel and rock must be located near the construction site. Topsoil and vegetation removed from the borrow pit is stockpiled for subsequent rehabilitation of the extraction area. Side slopes in excavation areas cannot be steeper than one vertical to two horizontal for safety reasons. Processes during earthwork include excavation removal of material filling compacting construction and trimming. If rock or unsuitable material is discovered it is removed moisture content managed and replaced with standard fill compacted to meet design requirements generally 90, 95% relative compaction. Geosynthetics such as geotextiles geogrids and geocells are frequently used in pavement layers to improve road quality. These materials perform four main functions: separation reinforcement filtration and drainage increasing performance while reducing costs. The completed roadway is finished by paving or left with a gravel or other natural surface depending on economic factors.
According to experiments called the AASHO Road Test carried out in the late 1950s effective damage done to the road is roughly proportional to the fourth power of axle weight. A typical tractor-trailer weighing 80,000 pounds does 7,800 times more damage than a passenger vehicle. In some parts of the United Kingdom the standard design life is 40 years for new bitumen and concrete pavement. Maintenance is considered at 10 20 and 30-year milestones with roads designed for lives ranging from 8 to 60 years. Some asphalt pavements built over 35 years ago have remained in good condition long past their design life. Chicago's Wacker Drive is being rebuilt with a designed service life of 100 years. Pro-active agencies use pavement management techniques to monitor conditions and schedule preventive maintenance treatments. Laser/inertial profilometers measure road curvature cross slope asperity roughness rutting and texture. Software algorithms use this data to recommend maintenance or new construction. Thin surfacing preserves protects and improves functional condition while reducing routing maintenance needs. Older concrete pavements developing faults can be repaired with dowel bar retrofit extending life by 15 years. Slab stabilization fills small voids beneath concrete slabs using cementitious grout or polyurethane mixture pumped through drilled holes. Ground penetrating radar pulses electromagnetic waves into pavement revealing voids and other defects visually. Joint sealing minimizes infiltration of surface water and incompressible material into the joint system.
Careful design and construction of roads can increase traffic safety and reduce harm from collisions. On neighborhood roads traffic calming safety barriers pedestrian crossings and cycle lanes help protect pedestrians cyclists and drivers. Lane markers in some countries are marked with Cat's eyes or Botts dots embedded in shallow trenches carved in mountainous regions of California. For major roads risk reduction involves limited access grade separated junctions and median dividers between opposite-direction traffic. Energy attenuation devices like guardrails wide grassy areas and sand barrels are commonly placed along highways. Light poles designed to break at base rather than violently stop a car that hits them. Highway authorities may remove larger trees from immediate vicinity of road to prevent obstruction during heavy rains. Speed limits improve road traffic safety and reduce casualties according to World Health Organization reports. Snow causing bad road conditions affects driving ease including quality of pavement potholes markings and weather. Weather conditions affect road conditions interlinked as noted by researchers Radu Popescu-Zeletin Karl Jonas and Idris A. Rai. Specific aspects include shadowing lighting changes texture changes and circular reflectors dashed lines solid lines for autonomous vehicles.
Road runoff is a major source of nickel copper zinc cadmium lead and polycyclic aromatic hydrocarbons created as combustion byproducts. De-icing chemicals and sand can run off into roadsides contaminating groundwater and polluting surface waters. Sand applied to icy roads ground up by traffic contributes to air pollution. Roads are a chief source of noise pollution recognized since the early 1970s when design could influence generation. Noise barriers reduce noise pollution near built-up areas while regulations restrict engine braking use. Motor vehicle emissions contribute air pollution with concentrations greater near roads than at distance away. Road dust kicked up by vehicles may trigger allergic reactions according to Science Daily reporting in 1999. On-road transportation greenhouse gas emissions represent the largest single cause of climate change scientists say. Water management systems reduce effect of pollutants from roads picking up gasoline motor oil heavy metals trash and other substances. Concentrations of air pollutants and adverse respiratory health effects are greater near the road than some distance away.
The United States has the largest network of roads of any country as of 2009. The Republic of India holds second-largest system globally with data from 2013. China ranks third with figures from 2007 while Brazil is fourth with 2002 statistics. As of 2017 China has 130,000 kilometers of Expressways second only to the United States. Eurasia Africa North America South America and Australia each have extensive networks connecting most cities. The North and South American road networks separated by Darién Gap remain the only interruption in Pan-American Highway. Eurasia and Africa connected by roads on Sinai Peninsula. European Peninsula linked to Scandinavian Peninsula via Øresund Bridge with many connections to mainland Eurasia including Bosphorus bridges. Antarctica has very few roads though ice roads exist between bases like South Pole Traverse. Bahrain connects to continental network via King Fahd Causeway to Saudi Arabia. Only 43% of rural Africans had access to all-season road as of 2014. Unpaved roads or lack thereof more common in developing countries becoming impassable in wet conditions. Roll-on/roll-off ferries commonly available for short journeys to disconnected islands while long trips use air transport.
Common questions
What is the definition of a road 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. This definition includes bridges, tunnels, supporting structures, junctions, crossings, interchanges, and toll roads but excludes cycle paths.
When was the world's oldest known paved road constructed in Egypt?
The world's oldest known paved road was constructed in Egypt some time between 2600 BC and 2200 BC. Corduroy roads dating back to 4000 BC exist in Glastonbury, England while the Sweet Track timber trackway in Northern Europe was built in winter 3807 BC or spring 3806 BC according to tree-ring dating.
How does axle weight affect damage to roads based on the AASHO Road Test experiments from the late 1950s?
Experiments called the AASHO Road Test carried out in the late 1950s show that effective damage done to the road is roughly proportional to the fourth power of axle weight. A typical tractor-trailer weighing 80,000 pounds does 7,800 times more damage than a passenger vehicle.
Which country has the largest network of roads as of 2009?
The United States has the largest network of roads of any country as of 2009. The Republic of India holds second-largest system globally with data from 2013 while China ranks third with figures from 2007.
What are the primary environmental impacts of road runoff and construction activities?
Road runoff is a major source of nickel copper zinc cadmium lead and polycyclic aromatic hydrocarbons created as combustion byproducts. De-icing chemicals and sand can run off into roadsides contaminating groundwater and polluting surface waters while motor vehicle emissions contribute air pollution with concentrations greater near roads than at distance away.