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top 10 words in brain distribution (in article): species animal bird male female breed human live light hunt |
top 10 words in brain distribution (in article): city power station state street Unite design town line light |
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top 10 words in brain distribution (not in article): build house store home water bus radio signal department frequency |
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| The cat'" ("Felis catus"), also known as the domestic cat'" or "'house cat'" to distinguish it from other felines and felids, is a small predatory carnivorous species of crepuscular mammal that is valued by humans for its companionship and its ability to hunt vermin, snakes, scorpions, and other unwanted household pests. It has been associated with humans for at least 9,500 years. A skilled predator, the cat is known to hunt over 1,000 species for food. It can be trained to obey simple commands. Individual cats have also been known to learn on their own to manipulate simple mechanisms, such as doorknobs. Cats use a variety of vocalizations and types of body language for communication, including meowing, purring, hissing, growling, squeaking, chirping, clicking, and grunting. Cats may be the most popular pet in the world, with over 600 million in homes all over the world. They are also bred and shown as registered pedigree pets. This hobby is known as the "cat fancy." Until recently the cat was commonly believed to have been domesticated in ancient Egypt, where it was a cult animal. However a 2007 study found that the lines of descent of all house cats probably run through as few as five self-domesticating African Wildcats "(Felis silvestris lybica)" circa 8000 BC, in the Near East. Size. Cats typically weigh between 2.5 and 7 kg (5.5–16 pounds); however, some, such as the Maine Coon, can exceed. Some have been known to reach up to due to overfeeding. Conversely, very small cats (less than) have been reported. The largest cat ever was officially reported to have weighed in at about (46 lb 15.25 oz). The smallest cat ever officially recorded weighed around 3 lbs (1.36 kg). Cats average about in height and in head body length (males being larger than females), with tails averaging in length. Skeleton. Cats have 7 cervical vertebrae like almost all mammals, 13 thoracic vertebrae (humans have 12), 7 lumbar vertebrae (humans have 5), 3 sacral vertebrae like most mammals (humans have 5 because of their bipedal posture), and, except for Manx cats, 22 or 23 caudal vertebrae (humans have 3 to 5, fused into an internal coccyx). The extra lumbar and thoracic vertebrae account for the cat's enhanced spinal mobility and flexibility, compared with humans. The caudal vertebrae form the tail, used by the cat as a counterbalance to the body during quick movements. Cats also have free-floating clavicle bones, which allows them to pass their body through any space into which they can fit their heads. Mouth. Cats have highly specialized teeth for the killing of prey and the tearing of meat. The premolar and first molar together compose the carnassial pair on each side of the mouth, which efficiently functions to shear meat like a pair of scissors. While this is present in canids, it is highly developed in felines. The cat's tongue has sharp spines, or papillae, useful for retaining and ripping flesh from a carcass. These papillae are small backward-facing hooks that contain keratin which also assist in their grooming. As facilitated by their oral structure, cats use a variety of vocalizations and types of body language for communication, including meowing, purring, hissing, growling, squeaking, chirping, clicking, and grunting. Ears. Thirty-two individual muscles in each ear allow for a manner of directional hearing: a cat can move each ear independently of the other. Because of this mobility, a cat can move its body in one direction and point its ears in another direction. Most cats have straight ears pointing upward. Unlike dogs, flap-eared breeds are extremely rare (Scottish Folds are one such exceptional mutation.) When angry or frightened, a cat will lay back its ears, to accompany the growling or hissing sounds it makes. Cats also turn their ears back when they are playing, or to listen to a sound coming from behind them. The angle of cats' ears is an important clue to their mood. Legs. Cats, like dogs, are digitigrades. They walk directly on their toes, with the bones of their feet making up the lower part of the visible leg. Cats are capable of walking very precisely, because like all felines they directly register; that is, they place each hind paw (almost) directly in the print of the corresponding forepaw, minimizing noise and visible tracks. This also provides sure footing for their hind paws when they navigate rough terrain. Claws. Like nearly all members of family Felidae, cats have protractable claws. In their normal, relaxed position the claws are sheathed with the skin and fur around the toe pads. This keeps the claws sharp by preventing wear from contact with the ground and allows the silent stalking of prey. The claws on the forefeet are typically sharper than those on the hind feet. Cats can voluntarily extend their claws on one or more paws. They may extend their claws in hunting or self-defense, climbing, "kneading", or for extra traction on soft surfaces (bedspreads, thick rugs, etc.). It is also possible to make a cooperative cat extend its claws by carefully pressing both the top and bottom of the paw. The curved claws may become entangled in carpet or thick fabric, which may cause injury if the cat is unable to free itself. Most cats have five claws on their front paws, and four or five on their rear paws. Because of an ancient mutation, however, domestic and feral cats are prone to polydactylyism, (particularly in the east coast of Canada and north east coast of the United States) and may have six or seven toes. The fifth front claw (the dewclaw) is proximal to the other claws. More proximally, there is a protrusion which appears to be a sixth "finger". This special feature of the front paws, on the inside of the wrists, is the carpal pad, also found on the paws of big cats and dogs. It has no function in normal walking, but is thought to be an anti-skidding device used while jumping. Skin. Cats possess rather loose skin; this allows them to turn and confront a predator or another cat in a fight, even when it has a grip on them. This is also an advantage for veterinary purposes, as it simplifies injections. In fact, the lives of cats with kidney failure can sometimes be extended for years by the regular injection of large volumes of fluid subcutaneously, which serves as an alternative to dialysis. The particularly loose skin at the back of the neck is known as the "scruff", and is the area by which a mother cat grips her kittens to carry them. As a result, cats tend to become quiet and passive when gripped there. This behavior also extends into adulthood, when a male will grab the female by the scruff to immobilize her while he mounts, and to prevent her from running away as the mating process takes place. This technique can be useful when attempting to treat or move an uncooperative cat. However, since an adult cat is heavier than a kitten, a pet cat should never be carried by the scruff, but should instead have its weight supported at the rump and hind legs, and at the chest and front paws. Often (much like a small child) a cat will lie with its head and front paws over a person's shoulder, and its back legs and rump supported under the person's arm. Senses. Cat senses are attuned for hunting. Cats have highly advanced hearing, eyesight, taste, and touch receptors, making the cat extremely sensitive among mammals. Cats' night vision is superior to humans although their vision in daylight is inferior. Cat eyes have a tapetum lucidum and cat eyes that are blue typically lack melanin and hence can show the red-eye effect (see odd-eyed cat). Humans and cats have a similar range of hearing on the low end of the scale, but cats can hear much higher-pitched sounds, up to 64 kHz, which is 1.6 octaves above the range of a human, and even one octave above the range of a dog. A domestic cat's sense of smell is about fourteen times as strong as a human's. Due to a mutation in an early cat ancestor, one of two genes necessary to taste sweetness may have been lost by the cat family. To aid with navigation and sensation, cats have dozens of movable vibrissae (whiskers) over their body, especially their face. Metabolism. Cats conserve energy by sleeping more than most animals, especially as they grow older. The daily duration of sleep varies, usually 12–16 hours, with 13–14 being the average. Some cats can sleep as much as 20 hours in a 24-hour period. The term "cat nap" refers to the cat's ability to fall asleep (lightly) for a brief period and has entered the English lexicon – someone who nods off for a few minutes is said to be "taking a cat nap". Due to their crepuscular nature, cats are often known to enter a period of increased activity and playfulness during the evening and early morning, dubbed the "evening crazies", "night crazies", "elevenses", or "mad half-hour" by some. The temperament of a cat can vary depending on the breed and socialization. Cats with oriental body types tend to be thinner and more active, while cats that have a cobby body type tend to be heavier and less active. The normal body temperature of a cat is between 38 and 39 °C (101 and 102.2 °F). A cat is considered febrile (hyperthermic) if it has a temperature of 39.5 °C (103 °F) or greater, or hypothermic if less than 37.5 °C (100 °F). For comparison, humans have a normal temperature of approximately 36.8 °C (98.6 °F). A domestic cat's normal heart rate ranges from 140 to 220 beats per minute, and is largely dependent on how excited the cat is. For a cat at rest, the average heart rate usually is between 150 and 180 bpm, about twice that of a human (average 80 bpm). Genetics. A 2007 study published in the journal "Science" asserts that all house cats are descended from a group of self-domesticating desert wildcats "Felis silvestris lybica" circa 10,000 years ago, in the Near East. The domesticated cat and its closest wild ancestor are both diploid organisms that possess 38 chromosomes, in which over 200 heritable genetic defects have been identified, many homologous to human inborn errors. Specific metabolic defects have been identified underlying many of these feline diseases. There are several genes responsible for the hair color identified. The combination of them gives different phenotypes. Features like hair length, lack of tail, or presence of a very short tail (bobtail cat) are also determined by single alleles and modified by polygenes. The Cat Genome Project, sponsored by the Laboratory of Genomic Diversity at the U.S. National Cancer Institute Frederick Cancer Research and Development Center in Frederick, Maryland, focuses on the development of the cat as an animal model for human hereditary disease, infectious disease, genome evolution, comparative research initiatives within the family Felidae, and forensic potential. All felines, including the big cats, have a genetic anomaly that may prevent them from tasting sweetness, which is a likely factor for their indifference to or avoidance of fruits, berries, and other sugary foods. Feeding and diet. Cats feed on small prey such as insects, birds, and rodents. Feral cats, or house cats who are free-fed, consume about 8 to 16 small meals in a single day. Despite this, adult cats can adapt to being fed once a day. Cats are classified as obligate carnivores, because their physiology is geared toward efficient processing of meat, and lacks efficient processes for digesting plant matter. The cat cannot produce its own taurine (an essential organic acid), and, as it is contained in flesh, the cat must eat flesh to survive (see Taurine and cats). Similarly as with its teeth, a cat's digestive tract has become specialized over time to suit meat eating, having shortened in length only to those segments of intestine best able to break down proteins and fats from animal flesh. This trait severely limits the cat's ability to properly digest, metabolize, and absorb plant-derived nutrients, as well as certain fatty acids. For example, taurine is scarce in plants but abundant in meats. It is a key amino sulfonic acid for eye health in cats. Taurine deficiency can cause a condition called macular degeneration wherein the cat's retina slowly degenerates, eventually causing irreversible blindness. Despite the cat's meat-oriented physiology, it is still quite common for a cat to supplement its carnivorous diet with small amounts of grass, leaves, shrubs, houseplants, or other plant matter. One theory suggests this behavior helps cats regurgitate if their digestion is upset; another is that it introduces fiber or trace minerals into the diet. In this context, caution is recommended for cat owners because some houseplants are harmful to cats. For example, the leaves of the Easter Lily can cause permanent and life-threatening kidney damage to cats, and Philodendron are also poisonous to cats. The Cat Fanciers' Association has a full list of plants harmful to cats. There are several vegetarian or vegan commercially available cat foods supplemented with chemically synthesized taurine and other added nutrients that attempt to address nutritional shortfalls. Cats can be selective eaters (which may be due in some way to the aforementioned mutation which caused their species to lose sugar-tasting ability). However, cats generally cannot tolerate lack of food for more than 36 hours without risking liver damage. Cats have a fondness for catnip, which is sensed by their olfactory systems. Many enjoy consuming catnip, and most will often roll in it, paw at it, and occasionally chew on it. Cats also can also develop odd eating habits. Some cats like to eat or chew on other things like plastic, paper, string, wool, or even coal. This condition is called pica and can threaten the cat's health depending on the amount and toxicity of the non-food items eaten. The condition's name comes from the Latin word for magpie, a bird which is reputed to eat almost anything. Toxic sensitivity. The liver of a cat is less effective at detoxification than those of other animals, including humans and dogs; therefore exposure to many common substances considered safe for households may be dangerous to them. In general, the cat's environment should be examined for the presence of such toxins and the problem corrected or alleviated as much as possible; in addition, where sudden or prolonged serious illness without obvious cause is observed, the possibility of toxicity must be considered, and the veterinarian informed of any such substances to which the cat may have had access. For instance, the common painkiller paracetamol or acetaminophen, sold under brand names such as Tylenol and Panadol, is extremely toxic to cats; because they naturally lack enzymes needed to digest it, even minute portions of doses safe for humans can be fatal and any suspected ingestion warrants immediate veterinary attention. Even aspirin, which is sometimes used to treat arthritis in cats, is much more toxic to them than to humans and must be administered cautiously. Similarly, application of minoxidil (Rogaine) to the skin of cats, either accidental or by well-meaning owners attempting to counter loss of fur, has sometimes proved fatal. In addition to such obvious dangers as insecticides and weed killers, other common household substances that should be used with caution in areas where cats may be exposed to them include mothballs and other naphthalene products, as well as phenol based products often used for cleaning and disinfecting near cats' feeding areas or litter boxes, such as Pine-Sol, Dettol (Lysol), hexachlorophene, "etc." which, although they are widely used without problem, have been sometimes seen to be fatal. Ethylene glycol, often used as an automotive antifreeze, is particularly appealing to cats, and as little as a teaspoonful can be fatal. Essential oils are toxic to cats and there have been reported cases of serious illnesses caused by tea tree oil, and tea tree oil-based flea treatments and shampoos. Many human foods are somewhat toxic to cats; theobromine in chocolate can cause theobromine poisoning, for instance, although few cats will eat chocolate. Toxicity in cats ingesting relatively large amounts of onions or garlic has also been reported. Even such seemingly safe | A train'" is a connected series of vehicles that move along a track (permanent way) to transport freight or passengers from one place to another. The track usually consists of two rails, but might also be a monorail or maglev guideway. Propulsion for the train is provided by a separate locomotive, or from individual motors in self-propelled multiple units. Most modern trains are powered by diesel locomotives or by electricity supplied by overhead wires or additional rails, although historically (from the early 19th century to the mid-20th century) the steam locomotive was the dominant form of locomotive power. Other sources of power (such as horses, rope or wire, gravity, pneumatics, and gas turbines) are possible. The word 'train' comes from the Old French "trahiner", itself from the Latin "trahere" 'pull, draw'. Types of trains. An electric locomotive -hauled freight train There are various types of train designed for particular purposes. A train can consist of a combination of one or more locomotives and attached railroad cars, or a self-propelled multiple unit (or occasionally a single powered coach, called a railcar). Trains can also be hauled by horses, pulled by a cable, or run downhill by gravity. Special kinds of trains running on corresponding special 'railways' are atmospheric railways, monorails, high-speed railways, maglev, rubber-tired underground, funicular and cog railways. A passenger train may consist of one or several locomotives, and one or more coaches. Alternatively, a train may consist entirely of passenger carrying coaches, some or all of which are powered as a "multiple unit". In many parts of the world, particularly Japan and Europe, high-speed rail is utilized extensively for passenger travel. Freight trains comprise wagons or trucks rather than carriages, though some parcel and mail trains (especially Travelling Post Offices) are outwardly more like passenger trains. Trains can also be 'mixed', comprising both passenger accommodation and freight vehicles. Such mixed trains are most likely to occur where services are infrequent, and running separate passenger and freight trains is not cost-effective, though the differing needs of passengers and freight usually means this is avoided where possible. Special trains are also used for track maintenance; in some places, this is called maintenance of way. In the United Kingdom, a train hauled by two locomotives is said to be "double-headed", and in Canada and the United States it is quite common for a long freight train to be headed by three or more locomotives. A train with a locomotive attached at each end is described as 'top and tailed', this practice typically being used when there are no reversing facilities available. Where a second locomotive is attached temporarily to assist a train up steep banks or grades (or down them by providing braking power) it is referred to as 'banking' in the UK, or 'helper service' in North America. Recently, many loaded trains in the US have been made up with one or more locomotives in the middle or at the rear of the train, operated remotely from the lead cab. This is referred to as "DP" or "Distributed Power." Official terminology. The railway terminology that is used to describe a 'train' varies between countries. In the United Kingdom, the interchangeable terms set'" and "'unit'" are used to refer to a group of permanently or semi-permanently coupled vehicles, such as those of a multiple unit. While when referring to a train made up of a variety of vehicles, or of several sets units, the term "'formation'" is used. (Although the UK public and media often forgo 'formation', for simply 'train'.) The word "'rake'" is also used for a group of coaches or wagons. In the United Kingdom Section 83(1) of the Railways Act 1993 defines "train" as follows: In the United States, the term "'consist'" is used to describe the group of rail vehicles which make up a train. When referring to motive power, "'consist'" refers to the group of locomotives powering the train. Similarly, the term "'trainset'" refers to a group of rolling stock that is permanently or semi-permanently coupled together to form a unified set of equipment (the term is most often applied to passenger train configurations). The Atchison, Topeka and Santa Fe Railway's 1948 operating rules define a train as: "An engine or more than one engine coupled, with or without cars, displaying markers." Motive power. The first trains were rope-hauled, gravity powered or pulled by horses, but from the early 19th century almost all were powered by steam locomotives. From the 1920s onwards they began to be replaced by less labour intensive and cleaner (but more complex and expensive) diesel locomotives and electric locomotives, while at about the same time self-propelled multiple unit vehicles of either power system became much more common in passenger service. In most countries dieselisation of locomotives in day-to-day use was completed by the 1970s. A few countries, most notably the People's Republic of China, where coal and labour are cheap, still use steam locomotives, but this is being gradually phased out. Historic steam trains still run in many other countries, for the leisure and enthusiast market. Electric traction offers a lower cost per mile of train operation but at a higher initial cost, which can only be justified on high traffic lines. Since the cost per mile of construction is much higher, electric traction is less favored on long-distance lines with the exception of long-distance high speed lines. Electric trains receive their current via overhead lines or through a third rail electric system. Passenger trains. A passenger train is one which includes passenger-carrying vehicles. It may be a self-powered multiple unit or railcar, or else a combination of one or more locomotives and one or more unpowered trailers known as coaches, cars or carriages. Passenger trains travel between stations where passengers may join or leave the train. The oversight of the train is the duty of a staff called the conductor. Many of the more prestigious passenger train services have been given a specific name, some of which have become famous in literature and fiction. India has the largest passenger density in the world. Some passenger trains, both long distance and short distanced, may use Bilevel car (double-decker) to hold more passengers per car. Designs and safety of passenger trains has changed dramatically over time. Long-distance trains. Long-distance trains travel between many cities and or regions of a country, and sometimes cross several countries. They often have a dining car or restaurant car to allow passengers to have a meal during the course of their journey. Trains traveling overnight may also have sleeping cars. High-speed trains. Russian Velaro high speed passenger train (a form of multiple unit) One notable and growing long-distance train category in the world is High-speed train. Generally they are faster than 200 km h and often use new separate passenger-only line of high grade standard. Shinkansen in Japan opened in 1964 is the first successful example of newly constructed High-speed train. The fastest train on rails is the French TGV (Train à Grande Vitesse) (French for High Speed Train) which achieved a speed of 574.8 km h (356 mph) in testing in 2007. The fastest commercial speed on rail is currently 350km h of Beijing–Tianjin Intercity Rail in China. TGV runs at a maximum commercial speed of 300-320 km h, as does the German ICE. Generally, High-speed rail is very competitive in less than 3 or 4 hours distance (ex; Tokyo – Osaka in Japan, 500km, 2h 30min, Paris- Lyon in France, 500 km, 2h) in corridor of dense population, but often air has advantage in longer journey. Very fast trains sometimes tilt, like the APT, the Pendolino, or the Talgo. Tilting is a system where the passenger cars automatically lean into curves, reducing the sideways g-forces on passengers and permitting higher speeds on curves in the track with greater passenger comfort. Maglev. In order to achieve much faster operation over 500 km h, innovative Maglev technology has been researched for years. Shanghai Maglev Train, opened in 2003, is the fastest one of 430km h operation. But Maglev has never operated to serve mass inter-city transit so far. Inter-city trains. Trains connecting cities can be distinguished into two groups, inter-city trains, which do not halt at small stations, and trains that serve all stations, usually known as local trains or "stoppers" (and sometimes an intermediate type, usually known as limited-stop). Regional trains. Regional trains usually connect between towns and cities, rather than purely linking major population hubs like inter-city train, and serve local traffic demand in relatively rural area. Commuter trains. For shorter distances many cities have networks of commuter trains, serving the city and its suburbs. Train is very efficient mode of transportation to cope with large traffic demand in metropolis. Compared with road transport, it carries many people with much smaller land area and little air pollution. Some carriages may be laid out to have more standing room than seats, or to facilitate the carrying of prams, cycles or wheelchairs. Some countries have double-decked passenger trains for use in conurbations. Double deck high speed and sleeper trains are becoming more common in mainland Europe. Sometimes extreme congestion of commuter trains becomes a problem. For example, an estimated 3.5 million passengers ride every day on Yamanote Line in Tokyo, Japan, with its 29 stations. For comparison, the New York City Subway carries 4.8 million passengers per day on 26 lines serving 468 stations. To cope with large traffic, special cars in which the bench seats fold up to provide standing room only during the morning rush hour (until 10 a.m.) are operated in Tokyo (E231 series train). This train has as many as six sets of doors on each side to shorten the time for passengers to get on and off at station. Passenger trains usually have emergency brake handles (or a "communication cord") that the public can operate. Misuse is punished by a heavy fine. Rapid transit. Large cities often have a metro system, also called underground, subway or tube. The trains are electrically powered, usually by third rail, and their railroads are separate from other traffic, without level crossings. Usually they run in tunnels in the city center and sometimes on elevated structures in the outer parts of the city. They can accelerate and decelerate faster than heavier, long-distance trains. The term "'rapid transit'" is used for public transport such as commuter trains, metro and light rail. However, in New York City, lines on the New York City Subway have been referred to as "trains". Tram. A light one- or two-car rail vehicle running through the streets is by convention not considered a train but rather a tram, trolley, light-rail vehicle or streetcar, but the distinction is not always strict. In some countries such as the United Kingdom the distinction between a tramway and a railway is precise and defined in law. Light rail. The term light rail is sometimes used for a modern tram, but it may also mean an intermediate form between a tram and a train, similar to metro except that it may have level crossings. These are often protected with crossing gates. They may also be called a trolley. Monorail. Monorail is developed to meet medium-demand traffic in urban transit, buts represent minor technologies in the train field. Named trains. Railway companies often give a name to a train service as a marketing exercise, to raise the profile of the service and hence attract more passengers (and also to gain kudos for the company). Usually, naming is reserved for the most prestigious trains: the high-speed express trains between major cities, stopping at few intermediate stations. The names of services such as the Orient Express, the Flying Scotsman, the Flèche d’Or and the Royal Scot have passed into popular culture. A somewhat less common practice is the naming of freight trains, for the same commercial reasons. The "Condor" was an overnight London-Glasgow express goods train, in the 1960s, hauled by pairs of "Metrovick" diesel locomotives. In the mid-1960s, British Rail introduced the "Freightliner" brand, for the new train services carrying containers between dedicated terminals around the rail network. The Rev. W. Awdry also named freight trains, coining the term "The Flying Kipper" for the overnight express fish train that appeared in his stories in The Railway Series books. Other trains of specific kinds. Heritage trains are operated by volunteers, often railfans, as a tourist attraction. Usually trains are a kind of historic value and retired practical operation. Most of them run weekend and vacation seasons. Airport trains are trains within airport buildings that transport people between terminals. Mine trains are operated in large mine and carry both workers and goods. Freight trains. A freight train (also known as goods train) uses "'freight cars (also known as wagons or trucks) to transport goods or materials (cargo) – essentially any train that is not used for carrying passengers. Much of the world's freight is transported by train, and in the USA the rail system is used more for transporting freight than passengers. Under the right circumstances, transporting freight by train is highly economic, and also more energy efficient than transporting freight by road. Rail freight is most economic when freight is being carried in bulk and over long distances, but is less suited to short distances and small loads. Bulk aggregate movements of a mere twenty miles (32 km) can be cost effective even allowing for trans-shipment costs. These trans-shipment costs dominate in many cases and many modern practices such as container freight are aimed at minimizing these. The main disadvantage of rail freight is its lack of flexibility. For this reason, rail has lost much of the freight business to road competition. Many governments are now trying to encourage more freight onto trains, because of the benefits that it would bring. There are many different types of freight trains, which are used to carry many different kinds of freight, with many different types of wagons. One of the most common types on modern railways are container trains, where containers can be lifted on and off the train by cranes and loaded off or onto trucks or ships. This type of freight train has largely superseded the traditional boxcar (wagon-load) type of freight train, with which the cargo has to be loaded or unloaded manually. In some countries "piggy-back" trains are used: trucks can drive straight onto the train and drive off again when the end destination is reached. A system like this is used through the Channel Tunnel between England and France, and for the trans-Alpine service between France and Italy (this service uses Modalohr road trailer carriers). 'Piggy-back' trains are the fastest growing type of freight trains in the United States, where they are also known as 'trailer on flatcar' or TOFC trains. 'Piggy-back' trains require no special modifications to the vehicles being carried. An alternative type of "inter-modal" vehicle, known as a Roadrailer, is designed to be physically attached to the train. The original trailers were fitted with two sets of wheels: one set flanged, for the trailer to run connected to other such trailers as a rail vehicle in a train; and one set tyred, for use as the semi-trailer of a road vehicle. More modern trailers have only road wheels and are designed to be carried on specially adapted bogies (trucks) when moving on rails. There are also many other types of wagons, such as "low loader" wagons for transporting road vehicles. There are refrigerator cars for transporting foods such as ice cream. There are simple types of open-topped wagons for transporting minerals and bulk material such as coal, and tankers for transporting liquids and gases. Today however most coal and aggregates are moved in hopper wagons that can be filled and discharged rapidly, to enable efficient handling of the materials. Freight trains are sometimes illegally boarded by passengers who do not wish to pay money, or do not have the money to travel by ordinary means. This is referred to as "hopping" and is considered by some communities to be a viable form of transport. Most hoppers sneak into train yards and stow away in boxcars. More bold hoppers will catch a train "on the fly", that is, as it is moving, leading to occasional fatalities. |