The Poles referred to as the Polish people, are a nation and West Slavic ethnic group native to Poland in Central Europe who share a common ancestry, culture and are native speakers of the Polish language. The population of self-declared Poles in Poland is estimated at 37,394,000 out of an overall population of 38,538,000, of whom 36,522,000 declared Polish alone. A wide-ranging Polish diaspora exists throughout Europe, the Americas, in Australasia. Today the largest urban concentrations of Poles are within the Warsaw and Silesian metropolitan areas. Poland's history dates back over a thousand years, to c. 930–960 AD, when the Polans – an influential West Slavic tribe in the Greater Poland region, now home to such cities as Poznań, Kalisz and Września – united various Lechitic tribes under what became the Piast dynasty, thus creating the Polish state. The subsequent Christianization of Poland, in 966 CE, marked Poland's advent to the community of Western Christendom. Poles have made important contributions to the world in every major field of human endeavor.
Notable Polish émigrés – many of them forced from their homeland by historic vicissitudes – have included physicists Marie Skłodowska Curie and Joseph Rotblat, mathematician Stanisław Ulam, pianists Fryderyk Chopin and Arthur Rubinstein, actresses Helena Modjeska and Pola Negri, novelist Joseph Conrad, military leaders Tadeusz Kościuszko and Casimir Pulaski, U. S. National Security Advisor Zbigniew Brzezinski, politician Rosa Luxemburg, filmmakers Samuel Goldwyn and the Warner Brothers, cartoonist Max Fleischer, cosmeticians Helena Rubinstein and Max Factor. Slavs have been in the territory of modern Poland for over 1500 years, they organized into tribal units, of which the larger ones were known as the Polish tribes. In the 9th and 10th centuries the tribes gave rise to developed regions along the upper Vistula, the Baltic Sea coast and in Greater Poland; the last tribal undertaking resulted in the 10th century in a lasting political structure and state, one of the West Slavic nations. The concept which has become known as the Piast Idea, the chief proponent of, Jan Ludwik Popławski, is based on the statement that the Piast homeland was inhabited by so-called "native" aboriginal Slavs and Slavonic Poles since time immemorial and only was "infiltrated" by "alien" Celts, Baltic peoples and others.
After 1945 the so-called "autochthonous" or "aboriginal" school of Polish prehistory received official backing in Poland and a considerable degree of popular support. According to this view, the Lusatian Culture which archaeologists have identified between the Oder and the Vistula in the early Iron Age, is said to be Slavonic. In contrast, the critics of this theory, such as Marija Gimbutas, regard it as an unproved hypothesis and for them the date and origin of the westward migration of the Slavs is uncharted. Polish people are the sixth largest national group in the European Union. Estimates vary depending on source, though available data suggest a total number of around 60 million people worldwide. There are 38 million Poles in Poland alone. There are Polish minorities in the surrounding countries including, indigenous minorities in the Czech Republic, Slovakia and eastern Lithuania, western Ukraine, western Belarus. There are some smaller indigenous minorities in nearby countries such as Moldova.
There is a Polish minority in Russia which includes indigenous Poles as well as those forcibly deported during and after World War II. The term "Polonia" is used in Poland to refer to people of Polish origin who live outside Polish borders estimated at around 10 to 20 million. There is a notable Polish diaspora in the United States and Canada. France has a historic relationship with Poland and has a large Polish-descendant population. Poles have lived in France since the 18th century. In the early 20th century, over a million Polish people settled in France during world wars, among them Polish émigrés fleeing either Nazi occupation or Soviet rule. In the United States, a significant number of Polish immigrants settled in Chicago, Detroit, New Jersey, New York City, Pittsburgh and New England; the highest concentration of Polish Americans in a single New England municipality is in New Britain, Connecticut. The majority of Polish Canadians have arrived in Canada since World War II; the number of Polish immigrants increased between 1945 and 1970, again after the end of Communism in Poland in 1989.
In Brazil the majority of Polish immigrants settled in Paraná State. Smaller, but significant numbers settled in the states of Rio Grande do Sul, Espírito Santo and São Paulo; the city of Curitiba has the second largest Polish diaspora in the world and Polish music and culture are quite common in the region. A recent large migration of Poles took place followi
An adhesion railway relies on adhesion traction to move the train. Adhesion traction is the friction between the steel rail; the term "adhesion railway" is only used when there is need to distinguish adhesion railways from railways moved by other means, e.g. by a stationary engine pulling on a cable attached to the cars, by railways which are moved by a pinion meshing with a rack, etc. This article focuses on the technical detail of what happens as a result of friction between the wheels and rails in what is known as the wheel-rail interface or contact patch. There are the good forces, e.g. the traction force, the braking forces, the centering forces, all of which contribute to stable running. There are the bad forces which increase costs by requiring more fuel consumption and increasing maintenance, needed to address fatigue damage, wear on rail heads and on the wheel rims, rail movement from traction and braking forces; the interface between the wheel and the rail is a specialist subject with continual research being done.
Traction or friction is reduced when the top of the rail is wet or frosty or contaminated with grease, oil or decomposing leaves which compact into a hard slippery lignin coating. Leaf contamination can be removed by applying "Sandite" from maintenance trains, using scrubbers and water jets, can be reduced with long-term management of railside vegetation. Locomotives and streetcars/trams use sand to improve traction. Adhesion is caused by friction, with maximum tangential force produced by a driving wheel before slipping given by: Fmax= coefficient of friction × Weight on wheelUsually the force needed to start sliding is greater than that needed to continue sliding; the former is concerned with static friction or "limiting friction", whilst the latter is dynamic friction called "sliding friction". For steel on steel, the coefficient of friction can be as high as 0.78, under laboratory conditions, but on railways it is between 0.35 and 0.5, whilst under extreme conditions it can fall to as low as 0.05.
Thus a 100-tonne locomotive could have a tractive effort of 350 kilonewtons, under the ideal conditions, falling to a 50 kilonewtons under the worst conditions. Steam locomotives suffer badly from adhesion issues because the traction force at the wheel rim fluctuates and, on large locomotives, not all wheels are driven; the "factor of adhesion", being the weight on the driven wheels divided by the theoretical starting tractive effort, was designed to be a value of 4 or higher, reflecting a typical wheel-rail friction coefficient of 0.25. A locomotive with a factor of adhesion much lower than 4 would be prone to wheelslip, although some 3-cylinder locomotives, such as the SR V Schools class, operated with a factor of adhesion below 4 because the traction force at the wheel rim do not fluctuate as much. Other factors affecting the likelihood of wheelslip include wheel size and the sensitivity of the regulator/skill of the driver; the term all-weather adhesion is used in North America, refers to the adhesion available during traction mode with 99% reliability in all weather conditions.
The maximum speed a train can proceed around a turn is limited by the radius of turn, the position of the centre of mass of the units, the wheel gauge and whether the track is superelevated or canted. Toppling will occur when the overturning moment due to the side force is sufficient to cause the inner wheel to begin to lift off the rail; this may result in loss of adhesion - preventing toppling. Alternatively, the inertia may be sufficient to cause the train to continue to move at speed causing the vehicle to topple completely. For a wheel gauge of 1.5 m, no canting, a centre of gravity height of 3 m and speed of 30 m/s, the radius of turn is 360 m. For a modern high speed train at 80 m/s, the toppling limit would be about 2.5 km. In practice, the minimum radius of turn is much greater than this, as contact between the wheel flanges and rail at high speed could cause significant damage to both. For high speed, the minimum adhesion limit again appears appropriate, implying a radius of turn of about 13 km.
In practice, curved lines used for high speed travel are superelevated or canted so that the turn limit is closer to 7 km. During the 19th century, it was believed that coupling the drive wheels would compromise performance and was avoided on engines intended for express passenger service. With a single drive wheelset, the Herzian contact stress between the wheel and rail necessitated the largest diameter wheels that could be accommodated; the weight of locomotive was restricted by the stress on the rail and sandboxes were required under reasonable adhesion conditions. It may be thought. However, close examination of a typical railway wheel reveals that the tread is burnished but the flange is not—the flanges make contact with the rail and, when they do, most of the contact is sliding; the rubbing of a flange on the track dissipates large amounts of energy as heat but including noise and, if sustained, would lead to excessive wheel wear. Centering is accomplished through shaping of the wheel.
The tread of the wheel is tapered. When the train is in the centre of the track, the region of the wheels in contact with the rail traces out a circle which has the same diameter for both wheels; the velocities of the two wheels are equal, so the train moves in a straight line. If, the wheelset is displaced to one side, the
In rail transport, head-end power known as electric train supply is the electrical power distribution system on a passenger train. The power source a locomotive at the front or'head' of a train, provides the electricity used for heating, lighting and other'hotel' needs; the maritime equivalent is hotel electric power. A successful attempt by the London and South Coast Railway in October 1881 to light the passenger car between London and Brighton heralded the beginning of using electricity to light trains in the world. Oil lamps were introduced in 1842 to light trains. Economics drove the Lancashire and Yorkshire Railway to replace oil with coal gas lighting in 1870, but a gas cylinder explosion on the train led them to abandon the experiment. Oil-gas lighting was introduced in late 1870. Electrical lighting was introduced in October 1881 by using twelve Swan carbon filament incandescent lamps connected to an underslung battery of 32 Faure lead-acid rechargeable cells, suitable for about 6 hours lighting before being removed for recharging.
The North British Railway in 1881 generated electricity using a dynamo on the Brotherhood steam locomotive to provide electrical lighting in a train, a concept, called head-end power. High steam consumption led to abandonment of the system. Three trains were started in 1883 by London and South Coast Railway with electricity generated on board using a dynamo driven from one of the axles; this charged a lead-acid battery in the guard's van, the guard operated and maintained the equipment. The system provided electric lighting in the train. In 1887, steam-driven generators in the baggage cars of the Florida Special and the Chicago Limited trains in the US supplied electric lighting to all the cars of the train by wiring them, to introduce the other form of head-end power; the oil-gas lighting provided a higher intensity of light compared to electric lighting and was more popularly used till September 1913, when an accident on the Midland Railway at Aisgill caused a large number of passenger deaths.
This accident prompted railways to adopt electricity for lighting the trains. Throughout the remainder of the age of steam and into the early diesel era, passenger cars were heated by low pressure saturated steam supplied by the locomotive, with the electricity for car lighting and ventilation being derived from batteries charged by axle-driven generators on each car, or from engine-generator sets mounted under the carbody. Starting in the 1930s, air conditioning became available on railcars, with the energy to run them being provided by mechanical power take offs from the axle, small dedicated engines or propane; the resulting separate systems of lighting power, steam heat, engine-driven air conditioning, increased the maintenance workload as well as parts proliferation. Head-end power would allow for a single power source to handle all those functions, more, for an entire train. In the steam era, all cars in Finland and Russia had a coal fired fireplace; such a solution was considered a fire danger in most countries in Europe, but not in Russia.
Trains hauled by a steam locomotive would be provided with a supply of steam from the locomotive for heating the carriages. When diesel locomotives and electric locomotives replaced steam, the steam heating was supplied by a steam-heat boiler; this was heated by an electric element. Oil-fired steam-heat boilers were unreliable, they caused more locomotive failures on any class to which they were fitted than any other system or component of the locomotive, this was a major incentive to adopt a more reliable method of carriage heating. At this time, lighting was powered by batteries which were charged by a dynamo underneath each carriage when the train was in motion, buffet cars would use bottled gas for cooking and water heating. Diesels and electric locomotives were equipped with Electric Train Heating apparatus, which supplied electrical power to the carriages to run electric heating elements installed alongside the steam-heat apparatus, retained for use with older locomotives. Carriage designs abolished the steam-heat apparatus, made use of the ETH supply for heating, ventilation, air conditioning, fans and kitchen equipment in the train.
In recognition of this ETH was renamed Electric Train Supply. Each coach has an index relating to the maximum consumption of electricity; the sum of all the indices must not exceed the index of the locomotive. One "ETH index unit" equals 5 kW; the first advance over the old axle generator system was developed on the Boston and Maine Railroad, which had placed a number of steam locomotives and passenger cars into dedicated commuter service in Boston. Due to the low average speeds and frequent stops characteristic of a commuter operation, the axle generators' output was insufficient to keep the batteries charged, resulting in passenger complaints about lighting and ventilation failures. In response, the railroad installed higher capacity generators on the locomotives assigned to these trains, provided electrical connections to the cars; the cars used steam from the locomotive for heating. Some early diesel streamliners took advantage of their fixed-consist construction to employ electrically-powered lighting, air conditioning, heating.
As the cars were not meant to mix with existing passenger stock, compatibility of these systems was not a concern. For example, the Nebraska Zephyr trainset has three diesel generator sets in the first car to power onboard equipment; when diese
Minimum railway curve radius
The minimum railway curve radius is the shortest allowable design radius for the center line of railway tracks under a particular set of conditions. It has an important bearing on constructions costs and operating costs and, in combination with superelevation in the case of train tracks, determines the maximum safe speed of a curve. Minimum radius of curve is one parameter in the design of railway vehicles as well as trams. Monorails and guideways are subject to minimum radii; the first proper railway was the Liverpool and Manchester Railway, which opened in 1830. Like the tram roads that had preceded it over a hundred years, the L&M had gentle curves and gradients. Among other reasons for the gentle curves were the lack of strength of the track, which might have overturned if the curves were too sharp causing derailments. There was no signalling at this time, so drivers had to be able to see ahead to avoid collisions with other trains on the line; the gentler the curves, the longer the visibility.
The earliest rails were made in short lengths of wrought iron, which does not bend like steel rails introduced in the 1850s. Minimum curve radii for railroads are governed by the speed operated and by the mechanical ability of the rolling stock to adjust to the curvature. In North America, equipment for unlimited interchange between railroad companies are built to accommodate 288-foot radius, but 410-foot radius is used as a minimum, as some freight cars are handled by special agreement between railroads that cannot take the sharper curvature. For handling of long freight trains, a minimum 574-foot radius is preferred; the sharpest curves tend to be on the narrowest of narrow gauge railways, where everything is proportionately smaller. As the need for more powerful locomotives grew, the need for more driving wheels on a longer, fixed wheelbase grew too, but long wheel bases are unfriendly to sharp curves. Various types of articulated locomotives were devised to avoid having to operate multiple locomotives with multiple crews.
More recent diesel and electric locomotives do not have a wheelbase problem and can be operated in multiple with a single crew. The Tasmanian Government Railways K class was 610 mm gauge 99 ft radius curves Example Garratt 1,000 mm gauge 25 kg/m rails Main line radius - 175 m Siding radius - 84 m 0-4-0 GER Class 209 1,435 mm Not all couplers can handle sharp curves; this is true of the European buffer and chain couplers, where the buffers extend the profile of the railcar body. For a line with maximum speed 60 km/h, buffer-and-chain couplings increase the minimum radius to around 150 m; as narrow gauge railways and metros do not interchange with mainline railroads, instances of these types of railroad in Europe use bufferless central couplers and build to a tighter standard. A long heavy freight train those with wagons of mixed loading, may struggle on sharp curves, as the drawgear forces may pull intermediate wagons off the rails. Common solutions include: marshalling light and empty wagons at rear of train intermediate locomotives, including remotely controlled ones.
Easing curves reduced. More, shorter trains. Equalizing wagon loading better driver training driving controls, and c2013 Electronically Controlled Pneumatic brakes. A similar problem occurs with harsh changes in gradients; as a heavy train goes round a bend at speed, the reactive centrifugal force can cause negative effects: passengers and cargo may feel unpleasant forces, the inside and outside rails will wear unequally, insufficiently anchored track may move. To counter this, a cant is used. Ideally the train should be tilted such that resultant force acts straight "down" through the bottom of the train, so the wheels, track and passengers feel little or no sideways force; some trains are capable of tilting to enhance this effect for passenger comfort. Because freight and passenger trains tend to move at different speeds, a cant cannot be ideal for both types of rail traffic; the relationship between speed and tilt can be calculated mathematically. We start with the formula for a balancing centripetal force: θ is the angle by which the train is tilted due to the cant, r is the curve radius in meters, v is the speed in meters per second, g is the standard gravity equal to 9.80665 m/s²: tan θ = v 2 g r Rearranging for r gives: r = v 2 g tan θ Geometrically, tan θ can be expressed in terms of the track gauge G, the cant ha and cant deficiency hb, all in millimeters: tan θ ≈ sin θ = h a + h b G This approximation for tan θ gives: r = v 2 g h a + h b G
Wrocław is a city in western Poland and the largest city in the historical region of Silesia. It lies on the banks of the River Oder in the Silesian Lowlands of Central Europe 350 kilometres from the Baltic Sea to the north and 40 kilometres from the Sudeten Mountains to the south; the population of Wrocław in 2018 was 639,258, making it the fourth-largest city in Poland and the main city of the Wrocław agglomeration. Wrocław is the historical capital of Lower Silesia. Today, it is the capital of the Lower Silesian Voivodeship; the history of the city dates back over a thousand years, its extensive heritage combines all religions and cultures of Europe. At various times, it has been part of the Kingdom of Poland, Kingdom of Bohemia, Kingdom of Hungary, Habsburg Monarchy and Germany. Wrocław became part of Poland again in 1945, as a result of the border changes after the Second World War, which included a nearly complete exchange of population. Wrocław is a university city with a student population of over 130,000, making it one of the most youthful cities in the country.
Since the beginning of the 20th century, the University of Wrocław Breslau University, produced 9 Nobel Prize laureates and is renowned for its high quality of teaching. Wrocław is classified as a Gamma-global city by GaWC, it was placed among the top 100 cities in the world for the quality of life by the consulting company Mercer and in the top 100 of the smartest cities in the world in the IESE Cities in Motion Index 2017 report. The city hosted the Eucharistic Congress in the Euro 2012 football championships. In 2016, the city was a European Capital of the World Book Capital. In this year, Wrocław hosted the Theatre Olympics, World Bridge Games and the European Film Awards. In 2017, the city was the host of the World Games; the city's name was first recorded as "Wrotizlava" in the chronicle of German chronicler Thietmar of Merseburg, which mentions it as a seat of a newly installed bishopric in the context of the Congress of Gniezno. The first municipal seal stated. A simplified name is given, as Wrezlaw, Prezla or Breslaw.
The Czech spelling was used in Latin documents as Vratislavia. At that time, Prezla was used in Middle High German. In the middle of the 14th century, the Early New High German form of the name, began to replace its earlier versions; the city is traditionally believed to be named after Wrocisław or Vratislav believed to be named after Duke Vratislaus I of Bohemia. It is possible that the city was named after the tribal duke of the Silesians or after an early ruler of the city called Vratislav; the city's name in various other languages is: Hungarian: Boroszló, Czech: Vratislav, German: Breslau, Hebrew: ורוצלב, Yiddish: ברעסלוי, Silesian German: Brassel, Latin: Vratislavia or Budorgis or Wratislavia. The city's name in other languages is available at the list of names of European cities. Persons born or living in the city are known as "Vratislavians". In ancient times at or near Wrocław was a place called Budorigum, it has been mapped to Claudius Ptolemy's map of AD 142–147. The city of Wrocław originated at the intersection of two trade routes, the Via Regia and the Amber Road.
Settlements in the area existed during the migration period. A Slavic tribe Ślężans erected on Ostrów Tumski a gord; the city was first recorded in the 10th century as Vratislavia, the Bohemian duke Vratislaus I founded here a Bohemian stronghold. Vratislavia was derived from the duke's name Vratislav. In 985, Duke Mieszko I of Poland conquered Silesia including Wrocław; the town was mentioned explicitly in the year 1000 AD in connection with a founding of a bishopric during the Congress of Gniezno. The medieval chronicle, Gesta principum Polonorum, written by Gallus Anonymus in 1112–1116, named Wrocław, along with Kraków and Sandomierz, as one of the three capitals of the Polish Kingdom. During Wrocław's early history, the control over it changed hands between Bohemia, the Kingdom of Poland, after the fragmentation of the Kingdom of Poland, the Piast-ruled duchy of Silesia. One of the most important events during this period was the foundation of the Diocese of Wrocław by the Polish Duke Bolesław the Brave in 1000.
Along with the Bishoprics of Kraków and Kołobrzeg, Wrocław was placed under the Archbishopric of Gniezno in Greater Poland, founded by Pope Sylvester II through the intercession of the Emperor Otto III in 1000, during the Congress of Gniezno. In the years 1034–1038 the city was affected by Pagan reaction in Poland; the city became a commercial centre and expanded to Wyspa Piasek, to the left bank of the River Oder. Around 1000, the town had about 1,000 inhabitants. In 1109 during the Polish-German war, Prince Bolesław III Wrymouth defeated the King of Germany Henry V at the Battle of Hundsfeld, stopping the German march into Poland. By 1139, a settlement belonging to Governor Piotr Włostowic was built, another was founded on the left bank of the River Oder, near the present seat of the University. While the city was Polish, there were communities of Bohemians, Jews and Germans. In the 13th century, Wrocław was the political centre of the divided Polish kingdom. In April 1241, during the First Mongol invasion of Poland the city was abandoned by the inhabitants and burned for strategic reason
The grade of a physical feature, landform or constructed line refers to the tangent of the angle of that surface to the horizontal. It is a special case of the slope. A larger number indicates higher or steeper degree of "tilt". Slope is calculated as a ratio of "rise" to "run", or as a fraction in which run is the horizontal distance and rise is the vertical distance; the grades or slopes of existing physical features such as canyons and hillsides and river banks and beds are described. Grades are specified for new linear constructions; the grade may refer to the perpendicular cross slope. There are several ways to express slope: as an angle of inclination to the horizontal; as a percentage, the formula for, 100 rise run which could be expressed as the tangent of the angle of inclination times 100. In the U. S. this percentage "grade" is the most used unit for communicating slopes in transportation, surveying and civil engineering. As a per mille figure, the formula for, 1000 rise run which could be expressed as the tangent of the angle of inclination times 1000.
This is used in Europe to denote the incline of a railway. As a ratio of one part rise to so many parts run. For example, a slope that has a rise of 5 feet for every 100 feet of run would have a slope ratio of 1 in 20.. This is the method used to describe railway grades in Australia and the UK, it is used for roads in Hong Kong, was used for roads in the UK until the 1970s. As a ratio of many parts run to one part rise, the inverse of the previous expression. For example, "slopes are expressed as ratios such as 4:1; this means that for every 4 units of horizontal distance there is a 1-unit vertical change either up or down."Any of these may be used. Grade is expressed as a percentage, but this is converted to the angle α from horizontal or the other expressions. Slope may still be expressed when the horizontal run is not known: the rise can be divided by the hypotenuse; this is not the usual way to specify slope. But in practice the usual way to calculate slope is to measure the distance along the slope and the vertical rise, calculate the horizontal run from that.
When the angle of inclination is small, using the slope length rather than the horizontal displacement makes only an insignificant difference. Railway gradients are expressed in terms of the rise in relation to the distance along the track as a practical measure. In cases where the difference between sin and tan is significant, the tangent is used. In any case, the following identity holds for all inclinations up to 90 degrees: tan α = sin α 1 − sin 2 α. In Europe, road gradients are signed as a percentage. Grades are related using the following equations with symbols from the figure at top. Tan α = Δ h d This ratio can be expressed as a percentage by multiplying by 100. Α = arctan Δ h d If the tangent is expressed as a percentage, the angle can be determined as: α = arctan % slope 100 If the angle is expressed as a ratio then: α = arctan 1 n In vehicular engineering, various land-based designs are rated for their ability to ascend terrain. Trains rate much lower than automobiles.
The highest grade a vehicle can ascend while maintaining a particular speed is sometimes termed that vehicle's "gradeability". The lateral slopes of a highway geometry are sometimes called fills or cuts where these techniques have been used to create them. In the United States, maximum grade for Federally funded highways is specified in a design table based on terrain and design speeds, with up to 6% allowed in mountainous areas and hilly urban areas with exceptions for up to 7% grades on mountainous roads with speed limits below 60 mph; the steepest roads in the world are Baldwin Street in Dunedin, New Zealand, Ffordd Pen Llech in Harlech and Canton Avenue in Pittsburgh, Pennsylvania. The Guinness World R
A pantograph is an apparatus mounted on the roof of an electric train, tram or electric bus to collect power through contact with an overhead line. It is a common type of current collector. A single or double wire is used, with the return current running through the track; the term stems from the resemblance of some styles to the mechanical pantographs used for copying handwriting and drawings. The pantograph, with a low-friction, replaceable graphite contact strip or'shoe' to minimise lateral stress on the contact wire, was invented in 1879 by Walter Reichel, chief engineer at Siemens & Halske in Germany. A flat slide-pantograph was invented in 1895 at the Baltimore and Ohio RailroadThe familiar diamond-shaped roller pantograph was invented by John Q. Brown of the Key System shops for their commuter trains which ran between San Francisco and the East Bay section of the San Francisco Bay Area in California, they appear in photographs of the first day of service, 26 October 1903. For many decades thereafter, the same diamond shape was used by electric-rail systems around the world and remains in use by some today.
The pantograph was an improvement on the simple trolley pole, which prevailed up to that time because the pantograph allows an electric-rail vehicle to travel at much higher speeds without losing contact with the overhead lines, e.g. due to dewirement of the trolley pole. Notwithstanding this, trolley pole current collection was used at up to 90 mph on the Electroliner vehicles of the Chicago North Shore and Milwaukee Railroad known as the North Shore Line; the most common type of pantograph today is the so-called half-pantograph, which evolved to provide a more compact and responsive single-arm design at high speeds as trains got faster. Louis Faiveley invented this type of pantograph in 1955; the half-pantograph can be seen in use on everything from fast trains to low-speed urban tram systems. The design operates with equal efficiency in either direction of motion, as demonstrated by the Swiss and Austrian railways whose newest high performance locomotives, the Re 460 and Taurus, operate with them set in the opposite direction.
The geometry and shape of the pantographs are specified by the EN 50367/IEC 60486 - Railway applications - Current collection systems - Technical criteria for the interaction between pantograph and overhead line. The electric transmission system for modern electric rail systems consists of an upper, weight-carrying wire from, suspended a contact wire; the pantograph is spring-loaded and pushes a contact shoe up against the underside of the contact wire to draw the current needed to run the train. The steel rails of the tracks act as the electrical return; as the train moves, the contact shoe slides along the wire and can set up standing waves in the wires which break the contact and degrade current collection. This means. Pantographs are the successor technology to trolley poles, which were used on early streetcar systems. Trolley poles are still used by trolleybuses, whose freedom of movement and need for a two-wire circuit makes pantographs impractical, some streetcar networks, such as the Toronto streetcar system, which have frequent turns sharp enough to require additional freedom of movement in their current collection to ensure unbroken contact.
However, many of these networks, including Toronto's, are undergoing upgrades to accommodate pantograph operation. Pantographs with overhead wires are now the dominant form of current collection for modern electric trains because, although more fragile than a third rail system, they allow the use of higher voltages. Pantographs are operated by compressed air from the vehicle's braking system, either to raise the unit and hold it against the conductor or, when springs are used to effect the extension, to lower it; as a precaution against loss of pressure in the second case, the arm is held in the down position by a catch. For high-voltage systems, the same air supply is used to "blow out" the electric arc when roof-mounted circuit breakers are used. Pantographs may have a double arm. Double-arm pantographs are heavier, requiring more power to raise and lower, but may be more fault-tolerant. On railways of the former USSR, the most used pantographs are those with a double arm, but since the late 1990s there have been some single-arm pantographs on Russian railways.
Some streetcars use double-arm pantographs, among them the Russian KTM-5, KTM-8, LVS-86 and many other Russian-made trams, as well as some Euro-PCC trams in Belgium. American streetcars use either trolley poles or single-arm pantographs. Most rapid transit systems are powered by a third rail, but some use pantographs ones that involve extensive above-ground running. Most hybrid metro-tram or'pre-metro' lines whose routes include tracks on city streets or in other publicly accessible areas, such as line 51 of the Amsterdam Metro, the MBTA Green Line, RTA Rapid Transit in Cleveland, Frankfurt am Main U-Bahn, San Francisco's Muni Metro, use overhead wire, as a standard third rail would obstruct street traffic and present too great a risk of electrocution. Among the various exceptions are several tram systems, such as the ones in Bordeaux, Angers and Dubai that use a proprietary underground system developed by Alstom, called APS, which only applies power to segments of track that are covered by the tram.
This system was designed to be used in the historic centre of Bordeaux because an overhead wire system would cause a visual intrusion. Similar systems that avoid overhead lines have been developed by Bombardier, AnsaldoBreda, CAF, and