Historic roads and trails
Historic roads are paths or routes that "have great historical importance or fame". Examples exist from prehistoric times until the early 20th century, they include ancient trackways and roads that existed in "the period of history before the fall of the Western Roman Empire" in 476 AD. "The first roads were paths made by animals and adapted by humans." Many historic routes, such as the Silk Road, the Amber Road, the Royal Road of the Persian Empire, existed before the Christian era and covered great distances. The Post Track, a prehistoric causeway in the valley of the River Brue in the Somerset Levels, England, is one of the oldest known constructed trackways and dates from around 3838 BCE; the world's oldest known paved road was constructed in Egypt some time between 2600 and 2200 BC. The Romans were the most significant road builders of the ancient world. At the peak of the Roman Empire there were more than 400,000 kilometres of roads, of which over 80,000 kilometres were stone-paved. Another empire, that of the Incas of pre-Columbian South America built an extensive and advanced transportation system.
Much historic roads include the Red River Trails between Canada and the US, from the 19th century. However, such pioneer trails in these countries made use of ancient routes created by indigenous people; the Silk Road was a major trade route between China and India and Arabia. It derives its name from the lucrative trade in silk carried out along its length, beginning in the Han dynasty; the Han dynasty expanded the Central Asian section of the trade routes around 114 BCE through the missions and explorations of the Chinese imperial envoy Zhang Qian. The Chinese took great interest in the safety of their trade products and extended the Great Wall of China to ensure the protection of the trade route. Prior to the Silk Road an ancient overland route existed through the Eurasian Steppe. Silk and horses were traded as key commodities; this route extended for 10,000 km. Trans-Eurasian trade through the Steppe Route precedes the conventional date for the origins of the Silk Road by at least two millennia.
See the Northern Silk Road, the Southern Silk Road: Through Khotan, Tea Horse Road. The Shudao, or the "Road to Shu", is a system of mountain roads linking the Chinese province of Shaanxi with Sichuan and maintained since the 4th century BC. Technical highlights were the gallery roads, consisting of wooden planks erected on wooden or stone beams slotted into holes cut into the sides of cliffs; the roads join three adjacent basins surrounded by high mountains. Like many ancient road systems, the Shu Roads formed a network of major and minor roads with different roads being used at different historical times. However, a number of roads are identified as the main routes. Kaidō were roads in Japan dating from the Edo period, they act important roles in transportation like the Appian way of ancient Roman roads. Major examples include the Edo Five Routes. Minor examples include sub-routes such as the Hokuriku Kaidō and the Nagasaki Kaidō. Kaidō, however, do not include San'yōdō, San'indō, Nankaidō and Saikaidō, which were part of the more ancient system of Yamato government called Gokishichidō.
This was the name for ancient administrative units and the roads within these units, organized in Japan during the Asuka period, as part of a legal and governmental system borrowed from the Chinese. Many highways and railway lines in modern Japan carry the same names; the early roads radiated from the capital at Kyoto. Edo was the reference, today Japan reckons directions and measures distances along its highways from Nihonbashi in Chūō, Tokyo; the Grand Trunk Road in South Asia was the main road from modern day Bangladesh to northern Pakistan and Afghanistan. A route since antiquity, it was constructed into a coherent highway by the Maurya Empire in 300BC. Soon after, the Greek diplomat Megasthenes wrote of his travels along the road to reach Hindu kingdoms in the 3rd century BC. After invading India over 1,500 years Mughals extended the Grand Trunk Road westwards from Lahore to Kabul crossing the Khyber Pass; the road was improved and extended from Calcutta to Peshawar by the British rulers of colonial India.
For many centuries, the road has acted as a major trade route and facilitated travel and postal communication. The Grand Trunk Road remains under use for transportation in India; the Khyber Pass was an all-season mountain pass connecting Afghanistan to western Pakistan. Brick-paved streets appeared in India as early as 3000 BC. Except for Roman roads, European pathways were in good shape and depended on the geography of the region. In the early Middle Ages, people preferred to travel along elevated drainage divides rather than in the valleys; this was due to other natural obstacles in valleys. The Amber Road was an ancient trade route for the transfer of amber from coastal areas of the North Sea and the Baltic Sea to the Mediterranean Sea. Prehistoric trade routes between Northern and Southern Europe were defined by the amber trade; as an important commodity, sometimes dubbed "the gold of the north", amber was transported overland by way of the Vistula and Dnieper rivers to the Mediterranean area from at least the 16th century BC.
The breast ornament of the Egyptian pharaoh Tutankhamen
Peat known as turf, is an accumulation of decayed vegetation or organic matter. It is unique to natural areas called peatlands, mires, moors, or muskegs; the peatland ecosystem is the most efficient carbon sink on the planet, because peatland plants capture CO2 released from the peat, maintaining an equilibrium. In natural peatlands, the "annual rate of biomass production is greater than the rate of decomposition", but it takes "thousands of years for peatlands to develop the deposits of 1.5 to 2.3 m, the average depth of the boreal peatlands". Sphagnum moss called peat moss, is one of the most common components in peat, although many other plants can contribute; the biological features of Sphagnum mosses act to create a habitat aiding peat formation, a phenomenon termed'habitat manipulation'. Soils consisting of peat are known as histosols. Peat forms in wetland conditions, where flooding obstructs the flow of oxygen from the atmosphere, slowing the rate of decomposition. Peatlands bogs, are the primary source of peat, although less-common wetlands including fens and peat swamp forests deposit peat.
Landscapes covered in peat are home to specific kinds of plants including Sphagnum moss, ericaceous shrubs, sedges. Because organic matter accumulates over thousands of years, peat deposits provide records of past vegetation and climate by preserving plant remains, such as pollen; this allows humans to reconstruct past environments and study changes in human land use. Peat is harvested as an important source of fuel in certain parts of the world. By volume, there are about 4 trillion cubic metres of peat in the world, covering a total of around 2% of the global land area, containing about 8 billion terajoules of energy. Over time, the formation of peat is the first step in the geological formation of other fossil fuels such as coal low-grade coal such as lignite. Depending on the agency, peat is not regarded as a renewable source of energy, due to its extraction rate in industrialized countries far exceeding its slow regrowth rate of 1 mm per year, as it is reported that peat regrowth takes place only in 30-40% of peatlands.
Because of this, the UNFCCC, another organization affiliated with the United Nations classified peat as a fossil fuel. However, the Intergovernmental Panel on Climate Change has begun to classify peat as a "slowly renewable" fuel; this is the classification used by many in the peat industry. At 106 g CO2/MJ, the carbon dioxide emission intensity of peat is higher than that of coal and natural gas. Peat forms when plant material does not decay in acidic and anaerobic conditions, it is composed of wetland vegetation: principally bog plants including mosses and shrubs. As it accumulates, the peat holds water; this creates wetter conditions that allow the area of wetland to expand. Peatland features can include ponds and raised bogs. Most modern peat bogs formed 12,000 years ago in high latitudes after the glaciers retreated at the end of the last ice age. Peat accumulates at the rate of about a millimetre per year. Peat material is either hemic, or sapric. Fibric peats are the least consist of intact fibre.
Hemic peats are decomposed and sapric are the most decomposed. Phragmites peat are composed of reed grass, Phragmites australis, other grasses, it is denser than many other types of peat. Engineers may describe a soil as peat which has a high percentage of organic material; this soil is problematic because it exhibits poor consolidation properties – it cannot be compacted to serve as a stable foundation to support loads, such as roads or buildings. In a cited article and Clarke defined peatlands or mires as...the most widespread of all wetland types in the world, representing 50 to 70% of global wetlands. They cover over 3 % of the land and freshwater surface of the planet. In these ecosystems are found one third of the world’s soil carbon and 10% of global freshwater resources; these ecosystems are characterized by the unique ability to accumulate and store dead organic matter from Sphagnum and many other non-moss species, as peat, under conditions of permanent water saturation. Peatlands are adapted to the extreme conditions of high water and low oxygen content, of toxic elements and low availability of plant nutrients.
Their water chemistry varies from alkaline to acidic. Peatlands occur on all continents, from the tropical to boreal and Arctic zones from sea level to high alpine conditions. Peatlands are areas of land with formed layers of peat, they can cover around 4 million square kilometres. In Europe, peatlands extend to about 515,000 km2. About 60% of the world's wetlands are made of peat. Peat deposits are found in many places around the world, including northern Europe and North America; the North American peat deposits are principally found in the Northern United States. Some of the world's largest peatlands include the West Siberian Lowland, the Hudson Bay Lowlands, the Mackenzie River Valley. There is less peat in part because there is less land; that said, the vast Magellanic Moorland in South America is an extensive peat-dominated landscape. Peat can be found in New Zealand
Yukon is the smallest and westernmost of Canada's three federal territories. It has the smallest population of any province or territory in Canada, with 35,874 people, although it has the largest city in any of the three territories. Whitehorse is Yukon's only city. Yukon was split from the Northwest Territories in 1898 and was named the Yukon Territory; the federal government's Yukon Act, which received royal assent on March 27, 2002, established Yukon as the territory's official name, though Yukon Territory is still popular in usage and Canada Post continues to use the territory's internationally approved postal abbreviation of YT. Though bilingual, the Yukon government recognizes First Nations languages. At 5,959 m, Yukon's Mount Logan, in Kluane National Park and Reserve, is the highest mountain in Canada and the second-highest on the North American continent. Most of Yukon has a subarctic climate, characterized by brief warm summers; the Arctic Ocean coast has a tundra climate. Notable rivers include the Yukon River, as well as the Pelly, Peel and Tatshenshini rivers.
The territory is named after the longest river in Yukon. The name itself is from a contraction of the words in the Gwich'in phrase chųų gąįį han, which means white water river and refers to "the pale colour" of glacial runoff in the Yukon River. Long before the arrival of Europeans and southern Yukon was populated by First Nations people, the area escaped glaciation. Sites of archeological significance in Yukon hold some of the earliest evidence of the presence of human habitation in North America; the sites safeguard the earliest First Nations of the Yukon. The volcanic eruption of Mount Churchill in 800 AD in what is now the U. S. state of Alaska blanketed southern Yukon with a layer of ash which can still be seen along the Klondike Highway, which forms part of the oral tradition of First Nations peoples in Yukon and further south in Canada. Coastal and inland First Nations had extensive trading networks. European incursions into the area began early in the 19th century with the fur trade, followed by missionaries.
By the 1870s and 1880s gold miners began to arrive. This drove a population increase that justified the establishment of a police force, just in time for the start of the Klondike Gold Rush in 1897; the increased population coming with the gold rush led to the separation of the Yukon district from the Northwest Territories and the formation of the separate Yukon Territory in 1898. The territory is the approximate shape of a right triangle, bordering the U. S. state of Alaska to the west and northwest for 1,210 km along longitude 141° W, the Northwest Territories to the east and British Columbia to the south. Its northern coast is on the Beaufort Sea, its ragged eastern boundary follows the divide between the Yukon Basin and the Mackenzie River drainage basin to the east in the Mackenzie mountains. Most of the territory is in the watershed of the Yukon River; the southern Yukon is dotted with a large number of large and narrow glacier-fed alpine lakes, most of which flow into the Yukon River system.
The larger lakes include Teslin Lake, Atlin Lake, Tagish Lake, Marsh Lake, Lake Laberge, Kusawa Lake and Kluane Lake. Bennett Lake on the Klondike Gold Rush trail is a lake flowing into Nares Lake, with the greater part of its area within Yukon. Canada's highest point, Mount Logan, is in the territory's southwest. Mount Logan and a large part of Yukon's southwest are in Kluane National Park and Reserve, a UNESCO World Heritage Site. Other national parks include Ivvavik National Vuntut National Park in the north. Other watersheds include the Mackenzie River, the Peel Watershed and the Alsek–Tatshenshini, a number of rivers flowing directly into the Beaufort Sea; the two main Yukon rivers flowing into the Mackenzie in the Northwest Territories are the Liard River in the southeast and the Peel River and its tributaries in the northeast. Notable widespread tree species within Yukon are white spruce. Many trees are stunted because of severe climate; the capital, Whitehorse, is the largest city, with about three-quarters of the population.
British Columbia Northwest Territories Alaska, United States While the average winter temperature in Yukon is mild by Canadian arctic standards, no other place in North America gets as cold as Yukon during extreme cold snaps. The temperature has dropped down to −60 °C three times, 1947, 1954, 1968; the most extreme cold snap occurred in February 1947 when the abandoned town of Snag dropped down to −63.0 °C. Unlike most of Canada where the most extreme heat waves occur in July and September, Yukon's extreme heat tends to occur in June and May. Yukon has recorded 36 °C three times; the first time was in June 1969 when Mayo recorded a temperature of 36.1 °C. 14 years this record was beaten when Forty Mile recorded 36 °C in May 1983. The old record was broken 21 years in June 2004 when the Mayo Road weather station, located just northwest of Whitehorse, recorded a temperature of 36.5 °C. The 2016 census reported a Yukon population of 35,874, an increase of 5.8% from 2011. With a land area of 474,712.64 km2, it had a population de
The horse is one of two extant subspecies of Equus ferus. It is an odd-toed ungulate mammal belonging to the taxonomic family Equidae; the horse has evolved over the past 45 to 55 million years from a small multi-toed creature, into the large, single-toed animal of today. Humans began domesticating horses around 4000 BC, their domestication is believed to have been widespread by 3000 BC. Horses in the subspecies caballus are domesticated, although some domesticated populations live in the wild as feral horses; these feral populations are not true wild horses, as this term is used to describe horses that have never been domesticated, such as the endangered Przewalski's horse, a separate subspecies, the only remaining true wild horse. There is an extensive, specialized vocabulary used to describe equine-related concepts, covering everything from anatomy to life stages, colors, breeds and behavior. Horses' anatomy enables them to make use of speed to escape predators and they have a well-developed sense of balance and a strong fight-or-flight response.
Related to this need to flee from predators in the wild is an unusual trait: horses are able to sleep both standing up and lying down, with younger horses tending to sleep more than adults. Female horses, called mares, carry their young for 11 months, a young horse, called a foal, can stand and run shortly following birth. Most domesticated horses begin training in harness between the ages of two and four, they reach full adult development by age five, have an average lifespan of between 25 and 30 years. Horse breeds are loosely divided into three categories based on general temperament: spirited "hot bloods" with speed and endurance. There are more than 300 breeds of horse in the world today, developed for many different uses. Horses and humans interact in a wide variety of sport competitions and non-competitive recreational pursuits, as well as in working activities such as police work, agriculture and therapy. Horses were used in warfare, from which a wide variety of riding and driving techniques developed, using many different styles of equipment and methods of control.
Many products are derived from horses, including meat, hide, hair and pharmaceuticals extracted from the urine of pregnant mares. Humans provide domesticated horses with food and shelter, as well as attention from specialists such as veterinarians and farriers. Specific terms and specialized language are used to describe equine anatomy, different life stages and breeds. Depending on breed and environment, the modern domestic horse has a life expectancy of 25 to 30 years. Uncommonly, a few animals live into their 40s and beyond; the oldest verifiable record was "Old Billy", a 19th-century horse that lived to the age of 62. In modern times, Sugar Puff, listed in Guinness World Records as the world's oldest living pony, died in 2007 at age 56. Regardless of a horse or pony's actual birth date, for most competition purposes a year is added to its age each January 1 of each year in the Northern Hemisphere and each August 1 in the Southern Hemisphere; the exception is in endurance riding, where the minimum age to compete is based on the animal's actual calendar age.
The following terminology is used to describe horses of various ages: Foal: A foal of either sex less than one year old. A nursing foal is sometimes called a suckling and a foal, weaned is called a weanling. Most domesticated foals are weaned at five to seven months of age, although foals can be weaned at four months with no adverse physical effects. Yearling: A horse of either sex, between one and two years old. Colt: A male horse under the age of four. A common terminology error is to call any young horse a "colt", when the term only refers to young male horses. Filly: A female horse under the age of four. Mare: A female horse four years old and older. Stallion: A non-castrated male horse four years old and older; the term "horse" is sometimes used colloquially to refer to a stallion. Gelding: A castrated male horse of any age. In horse racing, these definitions may differ: For example, in the British Isles, Thoroughbred horse racing defines colts and fillies as less than five years old. However, Australian Thoroughbred racing defines fillies as less than four years old.
The height of horses is measured at the highest point of the withers. This point is used because it is a stable point of the anatomy, unlike the head or neck, which move up and down in relation to the body of the horse. In English-speaking countries, the height of horses is stated in units of hands and inches: one hand is equal to 4 inches; the height is expressed as the number of full hands, followed by a point the number of additional inches, ending with the abbreviation "h" or "hh". Thus, a horse described; the size of horses varies by breed, but is influenced by nutrition. Light riding horses range in height from 14 to 16 hands and can weigh from 380 to 550 kilograms. Larger riding horses start at about 15.2 hands and are as tall as 17 hands, weighing from 500 to 600 kilograms. Heavy or draft horses are at least 16 hands (64 inches, 16
Old Plank Road
The Old Plank Road is a plank road in Imperial County, built in 1915 as an east–west route over the Algodones Dunes. It connected the extreme lower section of Southern California to Arizona and provided the last link in a commercial route between San Diego and Yuma. Following Los Angeles' winning the right to be the western terminus of the transcontinental railroad, San Diego's civic leaders proposed the Plank Road to ensure their city became the hub of Southern California's road network rather than Los Angeles. Among those promoters was businessman and road builder "Colonel" Ed Fletcher who accepted a challenge from the Los Angeles Examiner to run a road race in October 1912 to determine the best route between Southern California and Phoenix. A reporter with the paper was given a 24-hour head start in Los Angeles. Fletcher elected to traverse the shifting sand dunes using a team of horses to pull his automobile through the sand, won the race in a impossible 19.5 hours. Buoyed by the success of the race and with the backing of local newspapers, Fletcher raised the money to pay for 13,000 planks shipped from San Diego to Holtville, California.
The first planks were paid labor. The roadbed consisted of two parallel plank tracks, each 25 inches/63.5 cm wide, spiked to wooden crosspieces laid underneath. The total length of the Plank Road was 6.5 miles/10.4 km. Work ended nearly two months on April 4. Though traffic and maintenance crews who cleared the wooden road with mule-drawn scrapers soon took its toll on the planking, the road was considered a success. In June 1915, the California State Highway Commission assumed responsibility for the Plank Road as part of the road system linking Southern California with Arizona. A second, more sophisticated Plank Road was commissioned in 1916; the new roadway consisted of prefabricated wooden sections laid to a width of 8 feet/2.4 m with double-width turnouts every 1000 feet/305 m. The sections were shipped to the work site via horse-drawn wagon from their assembly point in nearby Ogilby, lowered into place using a crane. For the next ten years, work crews struggled against the elements to keep the Plank Road open.
The cost and difficulty of the maintenance coupled with improved road technology — not to mention the rough ride the planks created and the fact that the road was only wide enough for a single vehicle — meant that the days of the Plank Road were numbered. A new, 20-foot/6-meter-wide road with an asphaltic concrete surface constructed on top of a built-up sand embankment replaced the Old Plank Road upon its opening on August 12, 1926; the same roadway became displaced by U. S. Route 80, itself since displaced by Interstate 8. Today, only fragments of the Plank Road remain, they are protected under the jurisdiction of the Bureau of Land Management. Additionally, the fragments are both a California Historical Landmark and eligible for inclusion in the National Register of Historic Places. Remnants of the Plank Road may be seen at the west end of Grays Well Road, a frontage road south of I-8. A monument to the Plank Road and interpretive display lie three miles/5.4 km west of the Sand Hills interchange.
The monument's largest feature is a 1500-foot/457-meter-long replica of the road created in the early 1970s out of existing fragments. Plank Road history and photos
Hypoxia refers to low oxygen conditions. 20.9% of the gas in the atmosphere is oxygen. The partial pressure of oxygen in the atmosphere is 20.9% of the total barometric pressure. In water however, oxygen levels are much lower 1%, fluctuate locally depending on the presence of photosynthetic organisms and relative distance to the surface. Atmospheric hypoxia occurs at high altitudes. Total atmospheric pressure decreases as altitude increases, causing a lower partial pressure of oxygen, defined as hypobaric hypoxia. Oxygen remains at 20.9% of the total gas mixture, differing from hypoxic hypoxia, where the percentage of oxygen in the air is decreased. This is common, for example, in the sealed burrows of some subterranean animals, such as blesmols. Atmospheric hypoxia is the basis of altitude training, a standard part of training for elite athletes. Several companies mimic hypoxia using normobaric artificial atmosphere. Oxygen depletion is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system.
Dissolved oxygen is expressed as a percentage of the oxygen that would dissolve in the water at the prevailing temperature and salinity. An aquatic system lacking dissolved oxygen is termed reducing, or anoxic. Most fish cannot live below 30% saturation. Hypoxia leads to impaired reproduction of remaining fish via endocrine disruption. A "healthy" aquatic environment should experience less than 80%; the exaerobic zone is found at the boundary of hypoxic zones. Hypoxia can occur throughout the water column and at high altitudes as well as near sediments on the bottom, it extends throughout 20-50% of the water column, but depending on the water depth and location of pycnoclines. It can occur in 10-80% of the water column. For example, in a 10-meter water column, it can reach up to 2 meters below the surface. In a 20-meter water column, it can extend up to 8 meters below the surface. Oxygen depletion can result from a number of natural factors, but is most a concern as a consequence of pollution and eutrophication in which plant nutrients enter a river, lake, or ocean, phytoplankton blooms are encouraged.
While phytoplankton, through photosynthesis, will raise DO saturation during daylight hours, the dense population of a bloom reduces DO saturation during the night by respiration. When phytoplankton cells die, they sink towards the bottom and are decomposed by bacteria, a process that further reduces DO in the water column. If oxygen depletion progresses to hypoxia, fish kills can occur and invertebrates like worms and clams on the bottom may be killed as well. Hypoxia may occur in the absence of pollutants. In estuaries, for example, because freshwater flowing from a river into the sea is less dense than salt water, stratification in the water column can result. Vertical mixing between the water bodies is therefore reduced, restricting the supply of oxygen from the surface waters to the more saline bottom waters; the oxygen concentration in the bottom layer may become low enough for hypoxia to occur. Areas prone to this include shallow waters of semi-enclosed water bodies such as the Waddenzee or the Gulf of Mexico, where land run-off is substantial.
In these areas a so-called "dead zone" can be created. Low dissolved oxygen conditions are seasonal, as is the case in Hood Canal and areas of Puget Sound, in Washington State; the World Resources Institute has identified 375 hypoxic coastal zones around the world, concentrated in coastal areas in Western Europe, the Eastern and Southern coasts of the US, East Asia in Japan. Hypoxia may be the explanation for periodic phenomena such as the Mobile Bay jubilee, where aquatic life rushes to the shallows trying to escape oxygen-depleted water. Recent widespread shellfish kills near the coasts of Oregon and Washington are blamed on cyclic dead zone ecology. Scientists have determined that high concentrations of minerals dumped into bodies of water causes significant growth of phytoplankton blooms; as these blooms are broken down by bacteria, such as Phanerochaete chrysosprium, oxygen is depleted by the enzymes of these organisms. Phytoplankton are made up of lignin and cellulose, which are broken down by enzymes present in organisms such as P. chrysosprium, known as white-rot.
However, the breakdown of cellulose does not deplete oxygen concentration in water, whereas breakdown of lignin does. This breakdown of lignin includes an oxidative mechanism, requires the presence of dissolved oxygen to take place by enzymes like ligninperoxidase. Other fungi such as brown-rot, soft-rot, blue stain fungi are necessary in lignin transformation; as this oxidation takes place, CO2 is formed in its place Ligninperoxidase serves as the most import enzyme because it is best at breaking down lignin in these organisms. LiP disrupts C-C bonds and C-O bonds within Lignin’s three-dimensional structure, causing it to break down. LiP consists of ten alpha helices, two Ca2+ structural ions, as well as a heme group called a tetrapyrrol ring. Oxygen serves an important role in the catalytic cycle of LiP to form a double bond on the Fe2+ ion in the tetrapyrrol ring. Without the presence of diatomic oxygen in the water, this breakdown cannot
Chipseal is a pavement surface treatment that combines one or more layer of asphalt with one or more layer of fine aggregate. In the United States, chipseals are used on rural roads carrying lower traffic volumes, the process is referred to as asphaltic surface treatment. In Australia and New Zealand chipsealing is used on a larger percentage of roads, both rural and urban; this type of surface has a variety of other names including tar-seal or tarseal and chip, sprayed seal or surface dressing. Frederick Melrose Horowhenua Hanson developed the chipseal method in New Zealand where it became known as tar-seal in 1935 while working for the Public Works Department. Chipsealing is cheaper than resurfacing an asphalt concrete or a Portland cement concrete pavement, but not as long-lasting. Chipseals are constructed by evenly distributing a thin base of hot tar, bitumen or asphalt onto an existing pavement and embedding finely graded aggregate into it; the aggregate is evenly distributed over the hot seal spray rolled into the bitumen using heavy rubber tyred rollers creating a paved surface.
A chip-seal-surfaced pavement can optionally be sealed with a top layer, referred to as a fog seal or enrichment. The introduction of polymer-modified bitumen and emulsion binder has increased chipseal's ability to prevent crack reflection and improve stone retention by improving the properties of the bitumen binder. Newer techniques use asphalt emulsion instead of asphalt; this has been shown to help reduce aggregate loss and reduce cost of installation, but can increase stripping. It reduces emissions of volatile organic compounds due to the lower solvent content. New methods utilize cross linking styrene acrylic polymers which provide quality water resistance. Chips precoated with about one percent bitumen have been used to minimize aggregate loss and to give the surface a black look, it can keep good pavement in good condition by sealing out water, but provides no structural strength and will repair only minor cracks. While the small stones used as surface yield a even surface without the edges of patches, it results in a rough surface that leads to louder rolling noise from automobile wheels.
Although chipseal is an effective low-cost way to repair road, it has some drawbacks. Loose crushed stone is left on the surface, owing to underapplication of bitumen or overapplication of stone. If not removed, this can cause safety and environmental problems such as cracked windshields, chipped paint, loss-of-control crashes, deposition of foreign material into drainage courses. Therefore, it is important to sweep the road after the emulsion sets; as mentioned earlier, this problem can be minimized by using chips precoated with bitumen. Overapplication of emulsion can lead to bleeding, a condition where the excess asphalt rises to the surface, creating a smooth surface, slippery when wet and bubbling in the hotter summer months; as cars drive over it the tires kick up this tarry substance on to the side of the car. It can only be cleaned off with diesel fuel; the rough wearing surface of the chipseal generates more roadway noise at any operating speed than do typical asphalt or concrete surfaces.
These sound intensities increase with higher vehicle speeds. There is a considerable range in acoustical intensities produced depending upon the specific tire tread design and its interaction with the roadway surface type; the rough surface causes noticeable increases in vibration and rolling resistance for bicyclists, increased tire wear in all types of tires. Vehicle speed can affect the set up time with chipseal. Shortly after construction the set speed for chipseal is 10–15 miles per hour for the first 24–48 hours after construction. Macadam Asphalt Bituminous surface City of Grand Junction, CO page on Chipseal TRL Design Guide for Surface Dressing