Australia the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania and numerous smaller islands. It is the world's sixth-largest country by total area; the neighbouring countries are Papua New Guinea and East Timor to the north. The population of 25 million is urbanised and concentrated on the eastern seaboard. Australia's capital is Canberra, its largest city is Sydney; the country's other major metropolitan areas are Melbourne, Brisbane and Adelaide. Australia was inhabited by indigenous Australians for about 60,000 years before the first British settlement in the late 18th century, it is documented. After the European exploration of the continent by Dutch explorers in 1606, who named it New Holland, Australia's eastern half was claimed by Great Britain in 1770 and settled through penal transportation to the colony of New South Wales from 26 January 1788, a date which became Australia's national day; the population grew in subsequent decades, by the 1850s most of the continent had been explored and an additional five self-governing crown colonies established.
On 1 January 1901, the six colonies federated. Australia has since maintained a stable liberal democratic political system that functions as a federal parliamentary constitutional monarchy, comprising six states and ten territories. Being the oldest and driest inhabited continent, with the least fertile soils, Australia has a landmass of 7,617,930 square kilometres. A megadiverse country, its size gives it a wide variety of landscapes, with deserts in the centre, tropical rainforests in the north-east and mountain ranges in the south-east. A gold rush began in Australia in the early 1850s, its population density, 2.8 inhabitants per square kilometre, remains among the lowest in the world. Australia generates its income from various sources including mining-related exports, telecommunications and manufacturing. Indigenous Australian rock art is the oldest and richest in the world, dating as far back as 60,000 years and spread across hundreds of thousands of sites. Australia is a developed country, with the world's 14th-largest economy.
It has a high-income economy, with the world's tenth-highest per capita income. It is a regional power, has the world's 13th-highest military expenditure. Australia has the world's ninth-largest immigrant population, with immigrants accounting for 26% of the population. Having the third-highest human development index and the eighth-highest ranked democracy globally, the country ranks in quality of life, education, economic freedom, civil liberties and political rights, with all its major cities faring well in global comparative livability surveys. Australia is a member of the United Nations, G20, Commonwealth of Nations, ANZUS, Organisation for Economic Co-operation and Development, World Trade Organization, Asia-Pacific Economic Cooperation, Pacific Islands Forum and the ASEAN Plus Six mechanism; the name Australia is derived from the Latin Terra Australis, a name used for a hypothetical continent in the Southern Hemisphere since ancient times. When Europeans first began visiting and mapping Australia in the 17th century, the name Terra Australis was applied to the new territories.
Until the early 19th century, Australia was best known as "New Holland", a name first applied by the Dutch explorer Abel Tasman in 1644 and subsequently anglicised. Terra Australis still saw occasional usage, such as in scientific texts; the name Australia was popularised by the explorer Matthew Flinders, who said it was "more agreeable to the ear, an assimilation to the names of the other great portions of the earth". The first time that Australia appears to have been used was in April 1817, when Governor Lachlan Macquarie acknowledged the receipt of Flinders' charts of Australia from Lord Bathurst. In December 1817, Macquarie recommended to the Colonial Office. In 1824, the Admiralty agreed that the continent should be known by that name; the first official published use of the new name came with the publication in 1830 of The Australia Directory by the Hydrographic Office. Colloquial names for Australia include "Oz" and "the Land Down Under". Other epithets include "the Great Southern Land", "the Lucky Country", "the Sunburnt Country", "the Wide Brown Land".
The latter two both derive from Dorothea Mackellar's 1908 poem "My Country". Human habitation of the Australian continent is estimated to have begun around 65,000 to 70,000 years ago, with the migration of people by land bridges and short sea-crossings from what is now Southeast Asia; these first inhabitants were the ancestors of modern Indigenous Australians. Aboriginal Australian culture is one of the oldest continual civilisations on earth. At the time of first European contact, most Indigenous Australians were hunter-gatherers with complex economies and societies. Recent archaeological finds suggest. Indigenous Australians have an oral culture with spiritual values based on reverence for the land and a belief in the Dreamtime; the Torres Strait Islanders, ethnically Melanesian, obtained their livelihood from seasonal horticulture and the resources of their reefs and seas. The northern coasts and waters of Australia were visited s
A controlled-access highway is a type of highway, designed for high-speed vehicular traffic, with all traffic flow ingress- and egress-regulated. Common English terms are freeway and expressway. Other similar terms include parkway; some of these may be limited-access highways, although this term can refer to a class of highway with somewhat less isolation from other traffic. In countries following the Vienna convention, the motorway qualification implies that walking and parking are forbidden, they are reserved for the use of motorized vehicles only. A controlled-access highway provides an unhindered flow of traffic, with no traffic signals, intersections or property access, they are free of any at-grade crossings with other roads, railways, or pedestrian paths, which are instead carried by overpasses and underpasses. Entrances and exits to the highway are provided at interchanges by slip roads, which allow for speed changes between the highway and arterials and collector roads. On the controlled-access highway, opposing directions of travel are separated by a median strip or central reservation containing a traffic barrier or grass.
Elimination of conflicts with other directions of traffic improves safety and capacity. Controlled-access highways evolved during the first half of the 20th century. Italy opened its first autostrada in A8, connecting Milan to Varese. Germany began to build its first controlled-access autobahn without speed limits in 1932 between Cologne and Bonn, it rapidly constructed a nationwide system of such roads. The first North American freeways opened in the New York City area in the 1920s. Britain influenced by the railways, did not build its first motorway, the Preston By-pass, until 1958. Most technologically advanced nations feature an extensive network of freeways or motorways to provide high-capacity urban travel, or high-speed rural travel, or both. Many have a national-level or international-level system of route numbering. There are several international standards which give some definitions of words such as motorways, but there is no formal definition of the English language words such as "motorway", "freeway" and "expressway", or of the equivalent words in other languages such as "autoroute", "Autobahn", "autostrada", "autocesta", that are accepted worldwide—in most cases these words are defined by local statute or design standards or regional international treaties.
Descriptions that are used include: Vienna Convention on Road Signs and Signals"Motorway" means a road specially designed and built for motor traffic, which does not serve properties bordering on it, which:Is provided, except at special points or temporarily, with separate carriageways for the two directions of traffic, separated from each other either by a dividing strip not intended for traffic or, exceptionally, by other means. Exit is marked with another symbol:; the definitions of "motorway" from the OECD and PIARC are identical. British StandardsMotorway: Limited-access dual carriageway road, not crossed on the same level by other traffic lanes, for the exclusive use of certain classes of motor vehicle. ITE Freeway: A divided major roadway with full control of access and with no crossings at grade; this definition applies to toll as well as toll-free roads. Freeway A: This designates roadways with greater visual complexity and high traffic volumes; this type of freeway will be found in metropolitan areas in or near the central core and will operate through much of the early evening hours of darkness at or near design capacity.
Freeway B: This designates all other divided roadways with full control of access where lighting is needed. In the European Union, for statistic and safety purposes, some distinction might be made between motorway and expressway, for instance a principal arterial might be considered as: Roads serving long distance and interurban movements. Includes expressways. Principal arterials may cross through urban areas; the traffic is characterized by full or partial access control. Other roads leading to a principal arterial are connected to it through side collector roads. In this view, CARE's definition stands that a motorway is understood as a public road with dual carriageways and at least two lanes each way. All entrances and exits are signposted and all interchanges are grade separated. Central barrier or median present throughout the road. No crossing is permitted. Restricted access to motor vehicles, prohibited to pedestrians, pedal cycles, agricultural vehicles; the minimum speed is not lower than the maximum speed is not higher than 130 km/h.
Motorways are designed to carry heavy traffic at high speed with the lowest possible number of accidents. They are designed to collect long-distance traffic from other roads, so that conflicts between long-di
Steering is the collection of components, etc. which allows any vehicle to follow the desired course. An exception is the case of rail transport by which rail tracks combined together with railroad switches provide the steering function; the primary purpose of the steering system is to allow the driver to guide the vehicle. The most conventional steering arrangement is to turn the front wheels using a hand–operated steering wheel, positioned in front of the driver, via the steering column, which may contain universal joints, to allow it to deviate somewhat from a straight line. Other arrangements are sometimes found on different types of vehicles, for example, a tiller or rear–wheel steering. Tracked vehicles such as bulldozers and tanks employ differential steering—that is, the tracks are made to move at different speeds or in opposite directions, using clutches and brakes, to bring about a change of course or direction; the basic aim of steering is to ensure. This is achieved by a series of linkages, rods and gears.
One of the fundamental concepts is that of caster angle – each wheel is steered with a pivot point ahead of the wheel. The steering linkages connecting the steering box and the wheels conform to a variation of Ackermann steering geometry, to account for the fact that in a turn, the inner wheel is travelling a path of smaller radius than the outer wheel, so that the degree of toe suitable for driving in a straight path is not suitable for turns; the angle the wheels make with the vertical plane influences steering dynamics as do the tires. Many modern cars use rack and pinion steering mechanisms, where the steering wheel turns the pinion gear; this motion applies steering torque to the swivel pin ball joints that replaced used kingpins of the stub axle of the steered wheels via tie rods and a short lever arm called the steering arm. The rack and pinion design has the advantages of a large degree of feedback and direct steering "feel". A disadvantage is that it is not adjustable, so that when it does wear and develop lash, the only cure is replacement.
BMW began to use rack and pinion steering systems in the 1930s, many other European manufacturers adopted the technology. American automakers adopted pinion steering beginning with the 1974 Ford Pinto. Older designs use two main principles: the screw and nut. Both types were enhanced by reducing the friction; the steering column turns a large screw. The nut moves a sector of a gear; the recirculating ball version of this apparatus reduces the considerable friction by placing large ball bearings between the screw and the nut. The recirculating ball mechanism has the advantage of a much greater mechanical advantage, so that it was found on larger, heavier vehicles while the rack and pinion was limited to smaller and lighter ones; the recirculating ball design has a perceptible lash, or "dead spot" on center, where a minute turn of the steering wheel in either direction does not move the steering apparatus. This design is still in use in trucks and other large vehicles, where rapidity of steering and direct feel are less important than robustness and mechanical advantage.
The worm and sector was an older design, used for example in Willys and Chrysler vehicles, the Ford Falcon. To reduce friction the sector is replaced by rotating pins on the rocker shaft arm. Older vehicles use the recirculating ball mechanism, only newer vehicles use rack-and-pinion steering; this division is not strict and rack-and-pinion steering systems can be found on British sports cars of the mid-1950s, some German carmakers did not give up recirculating ball technology until the early 1990s. Other systems for steering are uncommon on road vehicles. Children's toys and go-karts use a direct linkage in the form of a bellcrank attached directly between the steering column and the steering arms, the use of cable-operated steering linkages is found on some home-built vehicles such as soapbox cars and recumbent tricycles. Power steering helps the driver of a vehicle to steer by directing some of its power to assist in swiveling the steered road wheels about their steering axes; as vehicles have become heavier and switched to
A car is a wheeled motor vehicle used for transportation. Most definitions of car say they run on roads, seat one to eight people, have four tires, transport people rather than goods. Cars came into global use during the 20th century, developed economies depend on them; the year 1886 is regarded as the birth year of the modern car when German inventor Karl Benz patented his Benz Patent-Motorwagen. Cars became available in the early 20th century. One of the first cars accessible to the masses was the 1908 Model T, an American car manufactured by the Ford Motor Company. Cars were adopted in the US, where they replaced animal-drawn carriages and carts, but took much longer to be accepted in Western Europe and other parts of the world. Cars have controls for driving, passenger comfort, safety, controlling a variety of lights. Over the decades, additional features and controls have been added to vehicles, making them progressively more complex; these include rear reversing cameras, air conditioning, navigation systems, in-car entertainment.
Most cars in use in the 2010s are propelled by an internal combustion engine, fueled by the combustion of fossil fuels. Electric cars, which were invented early in the history of the car, began to become commercially available in 2008. There are benefits to car use; the costs include acquiring the vehicle, interest payments and maintenance, depreciation, driving time, parking fees and insurance. The costs to society include maintaining roads, land use, road congestion, air pollution, public health, health care, disposing of the vehicle at the end of its life. Road traffic accidents are the largest cause of injury-related deaths worldwide; the benefits include on-demand transportation, mobility and convenience. The societal benefits include economic benefits, such as job and wealth creation from the automotive industry, transportation provision, societal well-being from leisure and travel opportunities, revenue generation from the taxes. People's ability to move flexibly from place to place has far-reaching implications for the nature of societies.
There are around 1 billion cars in use worldwide. The numbers are increasing especially in China and other newly industrialized countries; the word car is believed to originate from the Latin word carrus or carrum, or the Middle English word carre. In turn, these originated from the Gaulish word karros, it referred to any wheeled horse-drawn vehicle, such as a cart, carriage, or wagon. "Motor car" is attested from 1895, is the usual formal name for cars in British English. "Autocar" is a variant, attested from 1895, but, now considered archaic. It means "self-propelled car"; the term "horseless carriage" was used by some to refer to the first cars at the time that they were being built, is attested from 1895. The word "automobile" is a classical compound derived from the Ancient Greek word autós, meaning "self", the Latin word mobilis, meaning "movable", it entered the English language from French, was first adopted by the Automobile Club of Great Britain in 1897. Over time, the word "automobile" fell out of favour in Britain, was replaced by "motor car".
"Automobile" remains chiefly North American as a formal or commercial term. An abbreviated form, "auto", was a common way to refer to cars in English, but is now considered old-fashioned; the word is still common as an adjective in American English in compound formations like "auto industry" and "auto mechanic". In Dutch and German, two languages related to English, the abbreviated form "auto" / "Auto", as well as the formal full version "automobiel" / "Automobil" are still used — in either the short form is the most regular word for "car"; the first working steam-powered vehicle was designed — and quite built — by Ferdinand Verbiest, a Flemish member of a Jesuit mission in China around 1672. It was a 65-cm-long scale-model toy for the Chinese Emperor, unable to carry a driver or a passenger, it is not known with certainty if Verbiest's model was built or run. Nicolas-Joseph Cugnot is credited with building the first full-scale, self-propelled mechanical vehicle or car in about 1769, he constructed two steam tractors for the French Army, one of, preserved in the French National Conservatory of Arts and Crafts.
His inventions were, handicapped by problems with water supply and maintaining steam pressure. In 1801, Richard Trevithick built and demonstrated his Puffing Devil road locomotive, believed by many to be the first demonstration of a steam-powered road vehicle, it was unable to maintain sufficient steam pressure for long periods and was of little practical use. The development of external combustion engines is detailed as part of the history of the car but treated separately from the development of true cars. A variety of steam-powered road vehicles were used during the first part of the 19th century, including steam cars, steam buses and steam rollers. Sentiment against them led to the Locomotive Acts of 1865. In 1807, Nicéphore Niépce and his brother Claude created what was the world's first internal combustion engine, but they chose to install it in a boat on the river Saone in France. Coincidentally, in 1807 the Swiss inventor François Isaac de Rivaz designed his own'de Rivaz internal combustion engine' and used it to develop the world's first vehicle to be powered by such an engine.
Soil is a mixture of organic matter, gases and organisms that together support life. Earth's body of soil, called the pedosphere, has four important functions: as a medium for plant growth as a means of water storage and purification as a modifier of Earth's atmosphere as a habitat for organismsAll of these functions, in their turn, modify the soil; the pedosphere interfaces with the lithosphere, the hydrosphere, the atmosphere, the biosphere. The term pedolith, used to refer to the soil, translates to ground stone in the sense "fundamental stone". Soil consists of a solid phase of minerals and organic matter, as well as a porous phase that holds gases and water. Accordingly, soil scientists can envisage soils as a three-state system of solids and gases. Soil is a product of several factors: the influence of climate, relief and the soil's parent materials interacting over time, it continually undergoes development by way of numerous physical and biological processes, which include weathering with associated erosion.
Given its complexity and strong internal connectedness, soil ecologists regard soil as an ecosystem. Most soils have a dry bulk density between 1.1 and 1.6 g/cm3, while the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm3. Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic, although fossilized soils are preserved from as far back as the Archean. Soil science has two basic branches of study: pedology. Edaphology studies the influence of soils on living things. Pedology focuses on the formation and classification of soils in their natural environment. In engineering terms, soil is included in the broader concept of regolith, which includes other loose material that lies above the bedrock, as can be found on the Moon and on other celestial objects as well. Soil is commonly referred to as earth or dirt. Soil is a major component of the Earth's ecosystem; the world's ecosystems are impacted in far-reaching ways by the processes carried out in the soil, from ozone depletion and global warming to rainforest destruction and water pollution.
With respect to Earth's carbon cycle, soil is an important carbon reservoir, it is one of the most reactive to human disturbance and climate change. As the planet warms, it has been predicted that soils will add carbon dioxide to the atmosphere due to increased biological activity at higher temperatures, a positive feedback; this prediction has, been questioned on consideration of more recent knowledge on soil carbon turnover. Soil acts as an engineering medium, a habitat for soil organisms, a recycling system for nutrients and organic wastes, a regulator of water quality, a modifier of atmospheric composition, a medium for plant growth, making it a critically important provider of ecosystem services. Since soil has a tremendous range of available niches and habitats, it contains most of the Earth's genetic diversity. A gram of soil can contain billions of organisms, belonging to thousands of species microbial and in the main still unexplored. Soil has a mean prokaryotic density of 108 organisms per gram, whereas the ocean has no more than 107 procaryotic organisms per milliliter of seawater.
Organic carbon held in soil is returned to the atmosphere through the process of respiration carried out by heterotrophic organisms, but a substantial part is retained in the soil in the form of soil organic matter. Since plant roots need oxygen, ventilation is an important characteristic of soil; this ventilation can be accomplished via networks of interconnected soil pores, which absorb and hold rainwater making it available for uptake by plants. Since plants require a nearly continuous supply of water, but most regions receive sporadic rainfall, the water-holding capacity of soils is vital for plant survival. Soils can remove impurities, kill disease agents, degrade contaminants, this latter property being called natural attenuation. Soils maintain a net absorption of oxygen and methane and undergo a net release of carbon dioxide and nitrous oxide. Soils offer plants physical support, water, temperature moderation and protection from toxins. Soils provide available nutrients to plants and animals by converting dead organic matter into various nutrient forms.
A typical soil is about 50% solids, 50% voids of which half is occupied by water and half by gas. The percent soil mineral and organic content can be treated as a constant, while the percent soil water and gas content is considered variable whereby a rise in one is balanced by a reduction in the other; the pore space allows for the infiltration and movement of air and water, both of which are critical for life existing in soil. Compaction, a common problem with soils, reduces this space, preventing air and water from reaching plant roots and soil organisms. Given sufficient time, an undifferentiated soil will evolve a soil profile which consists of two or more layers, referred to as soil horizons, that differ in one or more properties such as in their texture, density, consistency, temperature and reactivity; the horizons differ in thickness and gene
New Zealand is a sovereign island country in the southwestern Pacific Ocean. The country geographically comprises two main landmasses—the North Island, the South Island —and around 600 smaller islands. New Zealand is situated some 2,000 kilometres east of Australia across the Tasman Sea and 1,000 kilometres south of the Pacific island areas of New Caledonia and Tonga; because of its remoteness, it was one of the last lands to be settled by humans. During its long period of isolation, New Zealand developed a distinct biodiversity of animal and plant life; the country's varied topography and its sharp mountain peaks, such as the Southern Alps, owe much to the tectonic uplift of land and volcanic eruptions. New Zealand's capital city is Wellington. Sometime between 1250 and 1300, Polynesians settled in the islands that were named New Zealand and developed a distinctive Māori culture. In 1642, Dutch explorer Abel Tasman became the first European to sight New Zealand. In 1840, representatives of the United Kingdom and Māori chiefs signed the Treaty of Waitangi, which declared British sovereignty over the islands.
In 1841, New Zealand became a colony within the British Empire and in 1907 it became a dominion. Today, the majority of New Zealand's population of 4.9 million is of European descent. Reflecting this, New Zealand's culture is derived from Māori and early British settlers, with recent broadening arising from increased immigration; the official languages are English, Māori, NZ Sign Language, with English being dominant. A developed country, New Zealand ranks in international comparisons of national performance, such as quality of life, education, protection of civil liberties, economic freedom. New Zealand underwent major economic changes during the 1980s, which transformed it from a protectionist to a liberalised free-trade economy; the service sector dominates the national economy, followed by the industrial sector, agriculture. Nationally, legislative authority is vested in an elected, unicameral Parliament, while executive political power is exercised by the Cabinet, led by the prime minister Jacinda Ardern.
Queen Elizabeth II is the country's monarch and is represented by a governor-general Dame Patsy Reddy. In addition, New Zealand is organised into 11 regional councils and 67 territorial authorities for local government purposes; the Realm of New Zealand includes Tokelau. New Zealand is a member of the United Nations, Commonwealth of Nations, ANZUS, Organisation for Economic Co-operation and Development, ASEAN Plus Six, Asia-Pacific Economic Cooperation, the Pacific Community and the Pacific Islands Forum. Dutch explorer Abel Tasman sighted New Zealand in 1642 and named it Staten Land "in honour of the States General", he wrote, "it is possible that this land joins to the Staten Land but it is uncertain", referring to a landmass of the same name at the southern tip of South America, discovered by Jacob Le Maire in 1616. In 1645, Dutch cartographers renamed the land Nova Zeelandia after the Dutch province of Zeeland. British explorer James Cook subsequently anglicised the name to New Zealand. Aotearoa is the current Māori name for New Zealand.
It is unknown whether Māori had a name for the whole country before the arrival of Europeans, with Aotearoa referring to just the North Island. Māori had several traditional names for the two main islands, including Te Ika-a-Māui for the North Island and Te Waipounamu or Te Waka o Aoraki for the South Island. Early European maps labelled the islands North and South. In 1830, maps began to use North and South to distinguish the two largest islands and by 1907 this was the accepted norm; the New Zealand Geographic Board discovered in 2009 that the names of the North Island and South Island had never been formalised, names and alternative names were formalised in 2013. This set the names as North Island or Te Ika-a-Māui, South Island or Te Waipounamu. For each island, either its English or Māori name can be used. New Zealand was one of the last major landmasses settled by humans. Radiocarbon dating, evidence of deforestation and mitochondrial DNA variability within Māori populations suggest New Zealand was first settled by Eastern Polynesians between 1250 and 1300, concluding a long series of voyages through the southern Pacific islands.
Over the centuries that followed, these settlers developed a distinct culture now known as Māori. The population was divided into iwi and hapū who would sometimes cooperate, sometimes compete and sometimes fight against each other. At some point a group of Māori migrated to Rēkohu, now known as the Chatham Islands, where they developed their distinct Moriori culture; the Moriori population was all but wiped out between 1835 and 1862 because of Taranaki Māori invasion and enslavement in the 1830s, although European diseases contributed. In 1862 only 101 survived, the last known full-blooded Moriori died in 1933; the first Europeans known to have reached New Zeala
A gravel road is a type of unpaved road surfaced with gravel, brought to the site from a quarry or stream bed. They are common in less-developed nations, in the rural areas of developed nations such as Canada and the United States. In New Zealand, other Commonwealth countries, they may be known as'metal roads', they may be referred to as'dirt roads' in common speech, but that term is used more for unimproved roads with no surface material added. If well constructed and maintained, a gravel road is an all-weather road. Compared to sealed roads, which require large machinery to work and pour concrete or to lay and smooth a bitumen-based surface, gravel roads are easy and cheap to build. However, compared to dirt roads, all-weather gravel highways are quite expensive to build, as they require front loaders, dump trucks and roadrollers to provide a base course of compacted earth or other material, sometimes macadamised, covered with one or more different layers of gravel. Graders are used used to "blade" the road's surface to produce a more extreme camber compared to a paved road to aid drainage, to produce an "A" shaped surface to the road called a "crown", as well as to construct drainage ditches and embankments in low-lying areas.
Cellular confinement systems can be used to prevent the washboarding effect. Construction of a gravel road begins with the subgrade layer; the expected road traffic volume and the average daily truck passage must be considered during the design process as they will influence the thickness of this layer, along with the balances of gravel and fines. Geotextile fabric may be laid to improve the stability of the subgrade layer; when geotextile fabric is used, a gravel layer with a minimum thickness of 6" is suggested to ensure the fabric remains unexposed. Road construction guidelines suggest that the crown in the road surface begins at the center point in the road, does not exceed a 4% gradation from the center to the edge of the roadway; the surface layer is constructed atop the subgrade layer. The amount of precipitation is taken into consideration for the selection of gravel size distribution; the surface layer will follow the crown established by the subgrade layer. Scarification of the subgrade layer prior to application of the surface gravel layer can be performed to increase the mixing and adherence between layers.
Construction of the road surface is done through multiple applications of layers of gravel, with compaction prior to the addition of the following layer. During reparation of a damaged road, ensuring that any washboarding, rutting and erosion is adequately removed will minimize future need for reparation. Windrowing can be performed along the edges of roads in dry climates to allow easy access to gravel material for small repairs; the gravel used consists of varying amount of crushed stone and fines. Fines are clay particles smaller than.075 millimetres, which can act as a binder. Crushed stone called road metal, is used because gravel with fractured faces will stay in place better than rounded river pebbles. A good gravel for a gravel road will have a higher percentage of fines than gravel used as a subbase for a paved road; this causes problems if a gravel road is paved without adding sand and gravel sized stone to dilute the percentage of fines. A gravel road is quite different from a'gravel drive', popular as private driveways in the United Kingdom.
This uses clean gravel consisting of small pebbles. In Africa and parts of Asia and South America, laterite soils are used to build dirt roads; however laterite, called murram in East Africa, varies in the proportion of stones to earth and sand. It ranges from a hard gravel to a softer earth embedded with small stones. Not all laterite and murram roads are therefore gravel roads. Laterite and murram which contains a significant proportion of clay becomes slippery when wet, in the rainy season, it may be difficult for four-wheel drive vehicles to avoid slipping off cambered roads into the drainage ditches at the side of the road; as it dries out, such laterite can become hard, like sun-dried bricks. Gravel roads require much more frequent maintenance than paved roads after wet periods and when accommodating increased traffic. Wheel motion shoves material to the outside, leading to rutting, reduced water-runoff, eventual road destruction if unchecked; as long as the process is interrupted early enough, simple re-grading is sufficient, with material being pushed back into shape.
Segments of gravel roads on grades rut as a result of flowing water. When grading or building the road, waterbars are used to direct water off the road; as an alternative method, humps can be formed in the gravel along the road to impede water flow, thereby reducing rutting. Another problem with gravel roads is washboarding — the formation of corrugations across the surface at right angles to the direction of travel. Narrow-spaced washboarding can develop on gravel roads due to inconsistent moisture levels in the gravel, poor quality gravel, vehicular stress to the road. Washboarding can occur when graders exceed recommended speeds during the construction or maintenance phase causing the blade to bounce on the surface creating a pattern of widely-spaced corrugations. Corrugations from washboarding can become severe enough to cause vibration in vehicles so that bolts loosen or cracks form in components. Proper grading is needed to remove the corrugations, reconstruction with careful choice of good quality gravel can help prevent them reforming.