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top 10 words in brain distribution (in article): species human male wolf time type state cell common body |
top 10 words in brain distribution (in article): city vehicle state people time wheel engine Unite car power |
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top 10 words in brain distribution (not in article): build church house store fuel love gear sexual god woman |
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times more probable under bee 30 20 10 6 4 2.5 1.25 1 1.25 2.5 4 6 10 20 30 times more probable under train (words not in the model) | |
| Bees'" are flying insects closely related to wasps and ants. Bees are a monophyletic lineage within the superfamily "'Apoidea'", presently classified by the unranked taxon name "'Anthophila'". There are nearly 20,000 known species of bee, in nine recognized families, though many are undescribed and the actual number is probably higher. They are found on every continent except Antarctica, in every habitat on the planet that contains insect-pollinated flowering plants. Introduction. Bees are adapted for feeding on nectar and pollen, the former primarily as an energy source, and the latter primarily for protein and other nutrients. Most pollen is used as food for larvae. Bees have a long proboscis (a complex "tongue") that enables them to obtain the nectar from flowers. They have antennae almost universally made up of 13 segments in males and 12 in females, as is typical for the superfamily. Bees all have two pairs of wings, the hind pair being the smaller of the two; in a very few species, one sex or caste has relatively short wings that make flight difficult or impossible, but none is wingless. The smallest bee is "Trigona minima", a stingless bee whose workers are about 2.1 mm (5 64") long. The largest bee in the world is "Megachile pluto", a leafcutter bee whose females can attain a length of 39 mm (1.5"). Members of the family Halictidae, or sweat bees, are the most common type of bee in the Northern Hemisphere, though they are small and often mistaken for wasps or flies. The best-known bee species is the European honey bee, which, as its name suggests, produces honey, as do a few other types of bee. Human management of this species is known as beekeeping or apiculture. Bees are the favorite meal of "Merops apiaster", the bee-eater bird. Other common predators are kingbirds, mockingbirds, bee wolves, and dragonflies. Pollination. Bees play an important role in pollinating flowering plants, and are the major type of pollinator in ecosystems that contain flowering plants. Bees either focus on gathering nectar or on gathering pollen depending on demand, especially in social species. Bees gathering nectar may accomplish pollination, but bees that are deliberately gathering pollen are more efficient pollinators. It is estimated that one third of the human food supply depends on insect pollination, most of which is accomplished by bees, especially the domesticated European honey bee. Contract pollination has overtaken the role of honey production for beekeepers in many countries. Monoculture and the massive decline of many bee species (both wild and domesticated) have increasingly caused honey bee keepers to become migratory so that bees can be concentrated in seasonally-varying high-demand areas of pollination. Most bees are fuzzy and carry an electrostatic charge, which aids in the adherence of pollen. Female bees periodically stop foraging and groom themselves to pack the pollen into the scopa, which is on the legs in most bees, and on the ventral abdomen on others, and modified into specialized pollen baskets on the legs of honey bees and their relatives. Many bees are opportunistic foragers, and will gather pollen from a variety of plants, while others are oligolectic, gathering pollen from only one or a few types of plant. A small number of plants produce nutritious floral oils rather than pollen, which are gathered and used by oligolectic bees. One small subgroup of stingless bees, called "vulture bees," is specialized to feed on carrion, and these are the only bees that do not use plant products as food. Pollen and nectar are usually combined together to form a "provision mass", which is often soupy, but can be firm. It is formed into various shapes (typically spheroid), and stored in a small chamber (a "cell"), with the egg deposited on the mass. The cell is typically sealed after the egg is laid, and the adult and larva never interact directly (a system called "mass provisioning"). Visiting flowers can be a dangerous occupation. Many assassin bugs and crab spiders hide in flowers to capture unwary bees. Other bees are lost to birds in flight. Insecticides used on blooming plants kill many bees, both by direct poisoning and by contamination of their food supply. A honey bee queen may lay 2000 eggs per day during spring buildup, but she also must lay 1000 to 1500 eggs per day during the foraging season, mostly to replace daily casualties, most of which are workers dying of old age. Among solitary and primitively social bees, however, lifetime reproduction is among the lowest of all insects, as it is common for females of such species to produce fewer than 25 offspring. The population value of bees depends partly on the individual efficiency of the bees, but also on the population itself. Thus, while bumblebees have been found to be about ten times more efficient pollinators on cucurbits, the total efficiency of a colony of honey bees is much greater, due to greater numbers. Likewise, during early spring orchard blossoms, bumblebee populations are limited to only a few queens, and thus are not significant pollinators of early fruit. Depopulation. Recently, managed populations of European honey bees have experienced substantial declines. This has prompted investigations into the phenomenon amidst great concern over the nature and extent of the losses. One aspect of the problem is believed to be "Colony Collapse Disorder" but many of the losses outside the US are attributed to other causes. Pesticides used to treat seeds, such as Clothianidin and Imidacloprid, may also negatively impact honey bee populations. Other species of bees such as mason bees are increasingly cultured and used to meet the agricultural pollination need. Most native pollinators are solitary bees, which often survive in refuge in wild areas away from agricultural spraying, but may still be poisoned in massive spray programs for mosquitoes, gypsy moths, or other insect pests. Evolution. Bees, like ants, are a specialized form of wasp. The ancestors of bees were wasps in the family Crabronidae, and therefore predators of other insects. The switch from insect prey to pollen may have resulted from the consumption of prey insects that were flower visitors and were partially covered with pollen when they were fed to the wasp larvae. This same evolutionary scenario has also occurred within the vespoid wasps, where the group known as "pollen wasps" also evolved from predatory ancestors. Up until recently the oldest non-compression bee fossil had been "Cretotrigona prisca" in New Jersey amber and of Cretaceous age, a meliponine. A recently reported bee fossil, of the genus "Melittosphex", is considered "an extinct lineage of pollen-collecting Apoidea sister to the modern bees", and dates from the early Cretaceous (~100 mya). Derived features of its morphology ("apomorphies") place it clearly within the bees, but it retains two unmodified ancestral traits ("plesiomorphies") of the legs (two mid-tibial spurs, and a slender hind basitarsus), indicative of its transitional status. The earliest animal-pollinated flowers were pollinated by insects such as beetles, so the syndrome of insect pollination was well established before bees first appeared. The novelty is that bees are "specialized" as pollination agents, with behavioral and physical modifications that specifically enhance pollination, and are generally more efficient at the task than beetles, flies, butterflies, pollen wasps, or any other pollinating insect. The appearance of such floral specialists is believed to have driven the adaptive radiation of the angiosperms, and, in turn, the bees themselves. Among living bee groups, the Dasypodaidae are now considered to be the most "primitive", and sister taxon to the remainder of the bees, contrary to earlier hypotheses that the "short-tongued" bee family Colletidae was the basal group of bees; the short, wasp-like mouthparts of colletids are the result of convergent evolution, rather than indicative of a plesiomorphic condition. Eusocial and semisocial bees. Bees may be solitary or may live in various types of communities. The most advanced of these are eusocial colonies found among the honey bees, bumblebees, and stingless bees. Sociality, of several different types, is believed to have evolved separately many times within the bees. In some species, groups of cohabiting females may be sisters, and if there is a division of labor within the group, then they are considered semisocial. If, in addition to a division of labor, the group consists of a mother and her daughters, then the group is called eusocial. The mother is considered the "queen" and the daughters are "workers". These castes may be purely behavioral alternatives, in which case the system is considered "primitively eusocial" (similar to many paper wasps), and if the castes are morphologically discrete, then the system is "highly eusocial". There are many more species of primitively eusocial bees than highly eusocial bees, but they have rarely been studied. The biology of most such species is almost completely unknown. The vast majority are in the family Halictidae, or "sweat bees". Colonies are typically small, with a dozen or fewer workers, on average. The only physical difference between queens and workers is average size, if they differ at all. Most species have a single season colony cycle, even in the tropics, and only mated females (future queens, or "gynes") hibernate (called diapause). A few species have long active seasons and attain colony sizes in the hundreds. The orchid bees include a number of primitively eusocial species with similar biology. Certain species of allodapine bees (relatives of carpenter bees) also have primitively eusocial colonies, with unusual levels of interaction between the adult bees and the developing brood. This is "progressive provisioning"; a larva's food is supplied gradually as it develops. This system is also seen in honey bees and some bumblebees. Highly eusocial bees live in colonies. Each colony has a single queen, many workers and, at certain stages in the colony cycle, drones. When humans provide the nest, it is called a hive. A honey bee hive can contain up to 40,000 bees at their annual peak, which occurs in the spring, but usually have fewer. Bumblebees. Bumblebees ("Bombus terrestris", "B. pratorum", et al.) are eusocial in a manner quite similar to the eusocial Vespidae such as hornets. The queen initiates a nest on her own (unlike queens of honey bees and stingless bees which start nests via swarms in the company of a large worker force). Bumblebee colonies typically have from 50 to 200 bees at peak population, which occurs in mid to late summer. Nest architecture is simple, limited by the size of the nest cavity (pre-existing), and colonies are rarely perennial. Bumblebee queens sometimes seek winter safety in honey bee hives, where they are sometimes found dead in the spring by beekeepers, presumably stung to death by the honey bees. It is unknown whether any survive winter in such an environment. Stingless bees. Stingless bees are very diverse in behavior, but all are highly eusocial. They practice mass provisioning, complex nest architecture, and perennial colonies. Honey bees. The true honey bees (genus "Apis") have arguably the most complex social behavior among the bees. The European (or Western) honey bee, "Apis mellifera", is the best known bee species and one of the best known of all insects. Africanized honey bee. Africanized bees, also called killer bees, are a hybrid strain of "Apis mellifera" derived from experiments to cross European and African honey bees by Warwick Estevam Kerr. Several queen bees escaped his laboratory in South America and have spread throughout the Americas. Africanized honey bees are more defensive than European honey bees. Solitary and communal bees. Most other bees, including familiar species of bee such as the Eastern carpenter bee ("Xylocopa virginica"), alfalfa leafcutter bee ("Megachile rotundata"), orchard mason bee ("Osmia lignaria") and the hornfaced bee ("Osmia cornifrons") are solitary in the sense that every female is fertile, and typically inhabits a nest she constructs herself. There are no "worker" bees for these species. Solitary bees typically produce neither honey nor beeswax. They are immune from acarine and "Varroa" mites (see diseases of the honey bee), but have their own unique parasites, pests and diseases. Solitary bees are important pollinators, and pollen is gathered for provisioning the nest with food for their brood. Often it is mixed with nectar to form a paste-like consistency. Some solitary bees have very advanced types of pollen carrying structures on their bodies. A very few species of solitary bees are being increasingly cultured for commercial pollination. Solitary bees are often oligoleges, in that they only gather pollen from one or a few species genera of plants (unlike honey bees and bumblebees which are generalists). No known bees are nectar specialists; many oligolectic bees will visit multiple plants for nectar, but there are no bees which visit only one plant for nectar while also gathering pollen from many different sources. Specialist pollinators also include bee species that gather floral oils instead of pollen, and male orchid bees, which gather aromatic compounds from orchids (one of the only cases where male bees are effective pollinators). In a very few cases only one species of bee can effectively pollinate a plant species, and some plants are endangered at least in part because their pollinator is dying off. There is, however, a pronounced tendency for oligolectic bees to be associated with common, widespread plants which are visited by multiple pollinators (e.g., there are some 40 oligoleges associated with creosotebush in the US desert southwest, and a similar pattern is seen in sunflowers, asters, mesquite, etc.) Solitary bees create nests in hollow reeds or twigs, holes in wood, or, most commonly, in tunnels in the ground. The female typically creates a compartment (a "cell") with an egg and some provisions for the resulting larva, then seals it off. A nest may consist of numerous cells. When the nest is in wood, usually the last (those closer to the entrance) contain eggs that will become males. The adult does not provide care for the brood once the egg is laid, and usually dies after making one or more nests. The males typically emerge first and are ready for mating when the females emerge. Providing nest boxes for solitary bees is increasingly popular for gardeners. Solitary bees are either stingless or very unlikely to sting (only in self defense, if ever). While solitary females each make individual nests, some species are gregarious, preferring to make nests near others of the same species, giving the appearance to the casual observer that they are social. Large groups of solitary bee nests are called "aggregations", to distinguish them from colonies. In some species, multiple females share a common nest, but each makes and provisions her own cells independently. This type of group is called "communal" and is not uncommon. The primary advantage appears to be that a nest entrance is easier to defend from predators and parasites when there are multiple females using that same entrance on a regular basis. Cleptoparasitic bees. Cleptoparasitic bees, commonly called "cuckoo bees" because their behavior is similar to cuckoo birds, occur in several bee families, though the name is technically best applied to the apid subfamily Nomadinae. Females of these bees lack pollen collecting structures (the scopa) and do not construct their own nests. They typically enter the nests of pollen collecting species, and lay their eggs in cells provisioned by the host bee. When the cuckoo bee larva hatches it consumes the host larva's pollen ball, and if the female cleptoparasite has not already done so, kills and eats the host larva. In a few cases where the hosts are social species, the cleptoparasite remains in the host nest and lays many eggs, sometimes even killing the host queen and replacing her. Many cleptoparasitic bees are closely related to, and resemble, their hosts in looks and size, (i.e., the "Bombus" subgenus "Psithyrus", which are parasitic bumblebees that infiltrate nests of species in other subgenera of "Bombus"). This common pattern gave rise to the ecological principle known as "Emery's Rule". Others parasitize bees in different families, like "Townsendiella", a nomadine apid, one species of which is a cleptoparasite of the dasypodaid genus "Hesperapis", while the other species in the same genus attack halictid bees. Nocturnal bees. Four bee families (Andrenidae, Colletidae, Halictidae, and Apidae) contain some species that are crepuscular (these may be either the vespertine or matinal type). These bees have greatly enlarged ocelli, which are extremely sensitive to light and | 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. |