History of trams
Tram, streetcar or trolley systems were common throughout the industrialized world in the late 19th and early 20th centuries, but they disappeared from many cities in the mid-20th century. In recent years, they have made a comeback. Many newer light rail systems share features with (or utilize) trams, although a distinction is often drawn between the two, especially if the line has significant off-street running.
- 1 Overview
- 2 Horse-drawn tramways
- 3 Girder rail
- 4 Horses to electric power
- 5 Electric trams
- 6 Disappearance from many cities
- 7 Return to grace
- 8 Technical developments
- 9 See also
- 10 References
The first tram was on the Swansea and Mumbles Railway in south Wales, United Kingdom. Horse-drawn at first, it was later powered by steam and electricity. In 1804, the Mumbles Railway Act was passed by the British Parliament, and the first tram (similar to streetcars in the US some 30 years later) was established and started operating in 1807.
The first streetcars, also known as horsecars in North America, were built in the United States and developed from city stagecoach and omnibus lines that picked up and dropped off passengers on a regular route without the need to be pre-hired. These trams were an animal railway, usually using horses and sometimes mules to haul the cars, usually two as a team. Occasionally other animals were put to use, or humans in emergencies. The first streetcar line, developed by Irish-American John Stephenson, was the Fourth Avenue Line of the New York and Harlem Railroad, which began operation in 1832 along Bowery and Fourth Avenue in New York City. A streetcar line was established in New Orleans, Louisiana in 1835, which is the oldest continuously operating street railway system in the world according to the American Society of Mechanical Engineers.
In 1883, Magnus Volk constructed the Volk's Electric Railway, a 2-ft gauge system along the eastern seafront in Brighton, England. This 2 km (1.2 mi) line was re-gauged to 2 ft 9 in (0.84 m) in 1884 and remains in service to this day as the oldest operating electric tramway in the world.
The first electric street tramway in Britain, the Blackpool Tramway, was opened on 29 September 1885 using conduit collection along Blackpool Promenade. After 1960, this remained the only first-generation operational tramway in the UK — it is still open.
Electric trams run in Budapest since 1887, and this first line has now grown to be the busiest tram line of Europe, with the tram cars following each other at an interval of 60 seconds at rush hour. Bucharest and Belgrade ran a regular service from 1894.
The very first passenger tram (streetcar) was the Swansea and Mumbles Railway, in Wales, UK. The Mumbles Railway Act was passed by the British Parliament in 1804, and this first horse-drawn passenger tramway (which acted like streetcars in the US some 30 years later) started operating in 1807. It was worked by steam from 1877, and then, from 1929, by very large (106-seater) electric tramcars, until closure in 1960.
The modern Tramlink in south London follows the route of the even older 1803 Surrey Iron Railway, a horsedrawn freight tramway sanctioned by Parliament in 1801, between Mitcham and Croydon. This gives Tramlink a claim to be one of the world's oldest tramways. (Tramway Path beside Mitcham tram stop had its name long before Tramlink was built). The Surrey Iron Railway was engineered by William Jessop, who had invented L-section iron rails in 1790, as an improvement on the wooden-railed wagonways which had been used in mines for centuries. These fish-bellied iron rails were manufactured by his assistant Benjamin Outram and it has been suggested that the word "Tramway" is a contraction of Outram's surname ("Outram Way"), but the term is much older and probably comes from the Low German word "traam" which means a "beam". (The first recorded surface-running horse-drawn wagonway was the 2-mile Wollaton Wagonway built in 1603-4 to carry coal from mines at Strelley down to the River Trent at Wollaton, near Nottingham, England).
The first streetcar in America, developed by John Stephenson, began service in the year 1832. This, the New York and Harlem Railroad's Fourth Avenue Line ran along the Bowery and Fourth Avenue in New York City. These streetcars, also known as horsecars in North America, were developed from city stagecoach lines and omnibus lines that picked up and dropped off passengers on a regular route and without the need to be pre-hired. These trams were an animal railway, usually using horses and sometimes mules to haul the cars, usually two as a team. Rarely other animals were tried, including humans in emergencies. It was followed in 1835 by New Orleans, Louisiana, which is the oldest continuously operating street railway system in the world, according to the American Society of Mechanical Engineers. At first the rails protruded above street level, causing accidents and major trouble for pedestrians. They were supplanted in 1852 by grooved rails or girder rails, invented by Alphonse Loubat.
The first tram in France was opened in 1839 between Montbrison and Montrond, on the streets inside the towns, and on the roadside outside town. It had permission for steam traction, but was entirely run with horse traction. In 1848, it was closed down after repeated economic failure. The first street trams in Britain were built in 1860 in Birkenhead by the eccentric American entrepreneur George Train, who later introduced street trams to London. If Africa's first tram service in Alexandria started on 8 January 1863.
One of the advantages over earlier forms of transit was the low rolling resistance of metal wheels on steel rails, allowing the animals to haul a greater load for a given effort. Problems included the fact that any given animal could only work so many hours on a given day, had to be housed, groomed, fed and cared for day in and day out, and produced prodigious amounts of manure, which the streetcar company was charged with disposing of. Since a typical horse pulled a car for perhaps a dozen miles a day and worked for four or five hours, many systems needed ten or more horses in stable for each horsecar. Electric trams largely replaced animal power in the late 19th and early 20th century. New York City had closed its last horsecar line in 1917. The last regular mule-drawn streetcar in the U.S., in Sulphur Rock, Arkansas, closed in 1926. However, during World War II some old horse cars were temporarily returned to service to help conserve fuel. A mule-powered line in Celaya, Mexico, operated until 1956.
The last example of a horse-drawn tram to be withdrawn from public service in the UK took passengers from Fintona railway station to Fintona Junction one mile away on the main Omagh to Enniskillen railway in Northern Ireland. The tram made its last journey on 30 September 1957 when the Omagh to Enniskillen line closed. The "van" now lies at the Ulster Transport Museum, but a silhouette of the old horse tram is still displayed on the signs at the entrance to the village.
Horse-drawn trams still operate on the 1876-built Douglas Bay Horse Tramway in the Isle of Man, and at the 1894 Victor Harbor Horse Drawn Tram, in Adelaide, South Australia. New horse-drawn systems have been established at the Hokkaidō Museum in Japan and also in Disneyland.
The tram developed in numerous cities of Europe (some of the most extensive systems were found in Berlin, Budapest, Birmingham, Leningrad, Lisbon, London, Manchester, Paris). Faster and more comfortable than the omnibus, trams had a high cost of operation because they were pulled by horses. That is why mechanical drives were rapidly developed, with steam power in 1873, and electrical after 1879 Berlin Trade Fair, where Siemens AG presented the first electric railway in which the power was supplied through the rails.
At first the rails protruded above street level, causing accidents and problems for pedestrians. They were supplanted in 1852 by grooved rails or girder rails, invented by Alphonse Loubat. Loubat, inspired by Stephenson, built the first tramline in Paris, France. The 2 km (1.2 mi) line was inaugurated on 21 November 1853, in connection with the 1855 World Fair, running on a trial basis from Place de la Concorde to Pont de Sèvres and later to the village of Boulogne. The Toronto streetcar system is one of the few in North America still operating in the classic style on street trackage shared with car traffic, where streetcars stop on demand at frequent stops like buses rather than having fixed stations. Known as Red Rockets because of their colour, they have been operating since the mid-19th century - horsecar service started in 1856 and electric service in 1892.
Horses to electric power
As many city streets were not paved at that time, normal carriages pulled by horses were often hindered by wet, muddy, or snowy conditions. One of the advantages of the horsecar tram over earlier forms of transit was the low rolling resistance of metal wheels on steel rails, allowing animals to haul a greater load for a given effort even in poor weather conditions. Problems included the fact that each animal could only work so many hours per day, had to be housed, groomed, fed and cared for day in and day out, and produced prodigious amounts of manure, which the streetcar company had to dispose of. Since a typical horse pulled a car for perhaps a dozen miles a day and worked for four or five hours, many systems needed ten or more horses for each horsecar. Electric trams largely replaced animal power in the late 19th and early 20th centuries. New York City closed its last horsecar line in 1917. The last regular mule-drawn streetcar in the U.S., in Sulphur Rock, Arkansas, closed in 1926. During World War II some old horse cars were temporarily returned to service to help conserve fuel. A mule-powered line in Celaya, Mexico, operated until 1956. Horse-drawn trams still operate as a tourist attraction along the promenade in Douglas, Isle of Man. There is also a small line on Main Street at Disney World, outside Orlando, Florida. A horse-drawn service 1300m long operates every 40 minutes at Victor Harbor, South Australia daily, with 20-minute services during tourist seasons, between the mainland and Granite Island across a 630m causeway. It uses double deck trams, and Clydesdale horses, and runs year round.
Trams subsequently developed in numerous cities, including London, Southampton, Berlin, Paris, Seoul, Kyoto, Tokyo, Hong Kong and Melbourne. Faster and more comfortable than the omnibus, trams had a high cost of operation because they were pulled by horses. That is why mechanical drives were rapidly developed, with steam power in 1873, and electricity after 1879 Berlin Trade Fair, where Siemens AG presented the first electric railway in which the power was supplied through the rails. Siemens AG continued developing and testing electric trams and eventually on May 16, 1881, Werner von Siemens opened the world's first electric tram line in Lichterfelde near Berlin, Germany.
The convenience and economy of electricity resulted in its rapid adoption once the technical problems of production and transmission of electricity were solved. As early as 1834, Thomas Davenport, a Vermont blacksmith, had invented a battery-powered electric motor which he later patented. The following year he used it to operate a small model electric car on a short section of track four feet in diameter. The first prototype of the electric tram was developed by Russian engineer Fyodor Pirotsky, who modified a horse tram to be powered by electricity. The invention was tested in 1880 in Saint Petersburg, Russia. In 1881, Werner von Siemens opened the world's first electric tram line in Lichterfelde near Berlin, Germany. For some time the German word for tram was simply "die Elektrische".
Parallel developments were occurring during the same period in the United States, where Frank J. Sprague and others contributed to inventions, including a system for collecting electricity from overhead wires. A spring-loaded trolley pole, invented in the US in 1885 by Charles Van Depoele, used a wheel to travel along the wire. Frank Sprague improved the designs, and in late 1887 and early 1888, using this trolley system, Sprague installed the first successful large electric street railway system, the Richmond Union Passenger Railway in Richmond, Virginia. By 1889, over a hundred electric railways incorporating Sprague's equipment had been begun or planned on several continents.
In Japan, the Kyoto Electric railroad was the first tram system, starting operation in 1895. By 1932, the network had grown to 82 railway companies in 65 cities, with a total network length of 1,479 km (919 mi). By the 1960s the tram had generally died out in Japan.
As for Ireland, from 1898 a tram service was in operation in Cork City but was discontinued in 1931 owing to the increased popularity of buses. There have been campaigns for the introduction of a service similar to the Luas in Dublin. but so far there has been little support for the idea, as the Dublin Bus service is extremely popular.
The world's first electric tram line operated in Sestroretsk near Saint Petersburg, Russia, invented and tested by Fyodor Pirotsky in 1880. The next line opened in Lichterfelde near Berlin, Germany, in 1881. It was built by Werner von Siemens (see Berlin Straßenbahn) who contacted Pirotsky. In Britain, Volk's electric railway was opened in 1883 in Brighton (see Volk's Electric Railway). Also in 1883, Mödling and Hinterbrühl Tram was opened near Vienna in Austria. It was the first tram and railway in the world in regular service that was run with electricity served by an overhead line with pantograph current collectors.
Multiple functioning experimental electric trams were exhibited at the 1884 World Cotton Centennial World's Fair in New Orleans, Louisiana, but they were not deemed good enough to replace the Lamm fireless engines then propelling the St. Charles Avenue Streetcar in that city.
In the US, electric trams (trolley cars) were first successfully tested in service in Richmond, Virginia, in 1888, in the Richmond Union Passenger Railway built by Frank J. Sprague. Another was by John Joseph Wright, brother of the famous mining entrepreneur Whitaker Wright, in Toronto in 1883. The first commercial installation of an electric streetcar in the United States was built in 1884 in Cleveland, Ohio and operated for a period of one year by the East Cleveland Street Railway Company. Earlier installations proved difficult or unreliable. Siemens’ line, for example, provided power through a live rail and a return rail, like a model train, limiting the voltage that could be used, and providing electric shocks to people and animals crossing the tracks. Siemens later designed his own version of overhead current collection, called the bow collector, and Thorold, Ontario, opened in 1887, and was considered quite successful at the time. While this line proved quite versatile as one of the earliest fully functional electric streetcar installations, it required horse-drawn support while climbing the Niagara Escarpment and for two months of the winter when hydroelectricity was not available. It continued in service in its original form into the 1950s.
Previously, other systems were larger. The tram system of Saint Petersburg, than Leningrad, at its summit in 1986 had 1022 km of lines and 2200 streetcars. In 2001 there were 700 km of lines on 285 km of trails. Berlin tram in 1929 had 634 km of trails, in 1948 there were 479,5 km, today there are only 189 km.
Since Sprague's installation was the first in the US to prove successful in all conditions, he is credited in the US with being the inventor of the trolley car; the Europeans might disagree, however (see Tram, History section). He later developed multiple unit control, first demonstrated in Chicago in 1897, allowing multiple cars to be coupled together and operated by a single motorman. This gave birth to the modern subway train.
Two rare but significant alternatives were conduit current collection, which was widely used in London, Washington, D.C. and New York, and the surface contact collection method, used in Wolverhampton (the Lorain system), Torquay and Hastings in the UK (the Dolter stud system), and currently in Bordeaux, France (the ground-level power supply system).
Attempts to use batteries as a source of electricity were made from the 1880s and 1890s, with unsuccessful trials conducted in among other places Bendigo and Adelaide in Australia, and for about 14 years as The Hague accutram of HTM in the Netherlands.
A Welsh example of a tram was usually known as the Mumbles Train, or more formally as the Swansea and Mumbles Railway. Built as the Oystermouth Railway in 1804, on March 25, 1807 it became the first passenger-carrying railway in the world. Converted to an overhead wire system it operated electric cars from March 2, 1929 until its closure on January 5, 1960. These were the largest tram cars built for use in Britain and seated 106 passengers.
The world's first hydroelectric powered tram system was the Giant's Causeway Tramway which originally ran from Portrush to Bushmills in Northern Ireland. At its opening in 1883 it was hailed as "the first long electric tramway in the world". Another early tram system operated from 1886 until 1930 in Appleton, Wisconsin, and is notable for being powered by the world's first hydroelectric power station, which began operating on September 30, 1882 as the Appleton Edison Electric Company.
There is one particular hazard associated with trams powered from a trolley off an overhead line. Since the tram relies on contact with the rails for the current return path, a problem arises if the tram is derailed or (more usually) if it halts on a section of track that has been particularly heavily sanded by a previous tram, and the tram loses electrical contact with the rails. In this event, the underframe of the tram, by virtue of a circuit path through ancillary loads (such as saloon lighting), is live at the full supply voltage, typically 600 volts. In British terminology such a tram was said to be ‘grounded’—not to be confused with the US English use of the term, which means the exact opposite. Any person stepping off the tram completed the earth return circuit and could receive a nasty electric shock. In such an event the driver was required to jump off the tram (avoiding simultaneous contact with the tram and the ground) and pull down the trolley before allowing passengers off the tram. Unless derailed, the tram could usually be recovered by running water down the running rails from a point higher than the tram. The water providing a conducting bridge between the tram and the rails.
In the 2000s, two companies introduced catenary-free designs. Alstom's Citadis line uses a third rail, and Bombardier's PRIMOVE LRV is charged by contactless induction plates embedded in the trackway.
Disappearance from many cities
The advent of personal motor vehicles and the improvements in motorized buses caused the rapid disappearance of the tram from most western and Asian countries by the end of the 1950s (for example the first major UK city to completely abandon its trams was Manchester by January 1949). Continuing technical and reliability improvements in buses made them a serious competitor to trams because they did not require the construction of costly infrastructure.  However, the demise of the streetcar came when lines were torn out of the major cities by "bus manufacturing or oil marketing companies for the specific purpose of replacing rail service with buses."
In many cases postwar buses were cited as providing a smoother ride and a faster journey than the older, prewar trams. For example, the tram network survived in Budapest but for a considerable period of time bus fares were higher to recognize the superior quality of the buses. However, many riders protested against the replacement of streetcars arguing that buses weren't as smooth or efficient and polluted the air. In the United States, there have been allegations that the Great American streetcar scandal was responsible for the replacement of trains with buses, but critics of this theory point to evidence that larger economic forces were driving conversion before General Motors' actions and outside of its reach. Certainly the oldest system of all, the Swansea and Mumbles Railway of 1807, was purchased by The South Wales Transport Company (which operated a large motor bus fleet in the area) and despite vociferous local opposition, closed down in 1960.
Governments thus put investment principally into bus networks. Indeed, infrastructure for roads and highways meant for the automobile were perceived as a mark of progress. The priority given to roads is illustrated in the proposal of French president Georges Pompidou who declared in 1971 that "the city must adapt to the car".
Tram networks were no longer maintained or modernized, a state of affairs that served to discredit them in the eyes of the public. Old lines, considered archaic, were then gradually replaced by buses.
Tram networks disappeared almost completely from France, the UK, and altogether from Ireland, Spain, as well as being completely removed from cities such as Sydney, which had one of the largest networks in the world with street mileage of 181 mi (291 km) and Brisbane. Most tram networks also disappeared in North America, but some cities still retained trams, such as Philadelphia, Newark, San Francisco, and Toronto. On the other hand, they were generally retained or modernized in most communist countries, as well as Switzerland, Germany, Austria, Italy, Belgium, the Netherlands, Portugal etc. In France, only the networks in Lille, Saint-Étienne and Marseille, survive from this period, but they all suffered significant reduction from their original size. In Great Britain, only the Blackpool Tramway kept the faith, with an extensive system which includes some street running in Blackpool, and a long stretch of segregated track to nearby Fleetwood.
- Closed completely in many countries like - Algeria, Denmark, Venezuela, Colombia, Chile, Ecuador, Paraguay, Bolivia, Cuba, Uruguay, Panama, Trinidad, Guyana, Jamaica, Armenia, Azerbaijan, Georgia, Singapore, Thailand, Philippines, South Korea, Shrilanka, Syria, Lebanon, Vietnam, Indonesia, Myanmar etc.
- Closed almost except one or two towns/cities like - Uzbekistan, India, Sweden etc.
- Previously closed but later returned as heritage system - South Africa, New Zealand, Peru etc.
- Previously closed but later returned as modern system - Tunisia etc.
- Some systems closed, some remains, some returned - Sweden, Egypt, Australia, Argentina, Brazil, North Korea, Turkey, China, Japan etc.
Return to grace
The priority given to personal vehicles and notably to the automobile led to a loss in quality of life, particularly in large cities where smog, traffic congestion, sound pollution and parking became problematic. Acknowledging this, some authorities saw fit to redefine their transport policies. Rapid transit required a heavy investment and presented problems in terms of subterranean spaces that required constant security. For rapid transit, the investment was mainly in underground construction, which made it impossible in some cities (with underground water reserves, archaeological remains, etc.). Metro construction thus was not a universal panacea.
The advantages of the tram thus became once again visible. At the end of the 1970s, some governments studied, and then built new tram lines. In France, Nantes and Grenoble lead the way in terms of the modern tram, and new systems were inaugurated in 1985 and 1988. The first UK modern street-operating light rail system opened in Manchester in 1992 with Italian built vehicles. In 1994 Strasbourg opened a system with novel British-built trams, specified by the city, with the goal of breaking with the archaic conceptual image that was held by the public.
The renaissance of light rail in North America began in 1978 when the Canadian city of Edmonton, Alberta adopted the German Siemens-Duewag U2 system, followed three years later by Calgary, Alberta and San Diego, California. Britain began replacing its run-down local railways with light rail in the 1980s, starting with the Tyne and Wear Metro in Tyneside and followed by the Docklands Light Railway in London. The trend to light rail in the United Kingdom was firmly established with the success of the Manchester Metrolink system and Sheffield Supertram in 1992, followed by Midland Metro in Birmingham in 1999, and Tramlink in London in 2000.
A great example of this shift in ideology is the city of Munich, which began replacing its tram network with a metro a few years before the 1972 Summer Olympics. When the metro network was finished in the 1990s the city began to tear out the tram network (which had become rather old and decrepit), but now faced opposition from many citizens who enjoyed the enhanced mobility of the mixed network—the metro lines deviate from the tram lines to a significant degree. New rolling stock was purchased and the system was modernized, and a new line was proposed in 2003.
It was the Olympic games of 2004 that prompted the redevelopment of trams as part of the Athens Mass Transit System. The tramways in Athens are among the most modern in the world, integrated with the revived Athens Metro system, as well as the buses, trolleybuses and suburban trains.
In Melbourne, Australia, the already extensive tramway system continues to be extended. In 2004 the Mont Albert line was extended several kilometres to Box Hill, whilst in 2005 the Burwood East line was extended several kilometres to Vermont South. In Sydney, trams returned in the form of light rail with the opening of the Inner West Light Rail line in 1997, which has seen extensions and now covers 7.2 mi (11.6 km).
In Scotland, Edinburgh relaunched its tram network on 31st May 2014 after delayed development which began in 2008. Edinburgh previously had an extensive tram network which began closure in the 1950s. The new network is significantly smaller, 8.7 miles, compared to the previous tram network, 47.25 miles.
Modern trams generally use overhead electric cables, from which they draw current through a pantograph, a bow collector (less commonly) or the now-rare trolley pole (the pantograph is most common and used on new tram designs). There are other methods of powering electric trams, sometimes preferred for aesthetic reasons since poles and overhead wires are not required. The old tram systems in London, Manhattan (New York City), and Washington, D.C., used live rails, like those on third-rail electrified railways, but in a conduit underneath the road, from which they drew power through a plough. It was called Conduit current collection. Washington's was the last of these to close, in 1962. Today, no commercial tramway uses this system. More recently, a modern equivalent to the old stud systems has been developed which allows for the safe installation of a third rail on city streets, which is known as surface current collection or ground-level power supply; the main example of this is the new tramway in Bordeaux.
In narrow situations double-track tram lines sometimes reduce to single track, or, to avoid switches, have the tracks interlaced, e.g. in the Leidsestraat in Amsterdam on three short stretches (see map detail); this is known as interlaced or gauntlet track. There is a UK example of interlaced track on the Tramlink, just west of Mitcham Station, where the formation is narrowed by an old landslip causing an obstruction. (See photo in Tramlink entry).
Traditionally trams had high floors, requiring passengers to climb several steps in order to board, but since the 1990s this design has been largely replaced by low-floor trams, or occasionally by high-floor trams with level boarding platforms, as in Manchester's Metrolink and some parts of Cologne's network, which allow passengers in wheelchairs or with perambulators to access vehicles more easily. In some jurisdictions this has even been made mandatory since the 1990s, for example by the HMRI in Britain and the Disability discrimination act in the United Kingdom and other Commonwealth countries.
Historically, the rail gauge has had considerable variations, with narrow gauge common in many early systems. However, most light rail systems are now standard gauge. An important advantage of standard gauge is that standard railway maintenance equipment can be used on it, rather than custom-built machinery. Using standard gauge also allows light rail vehicles to be delivered and relocated conveniently using freight railways and locomotives. Another factor favoring standard gauge is that low-floor vehicles are becoming popular, and there is generally insufficient space for wheelchairs to move between the wheels in a narrow gauge layout.
Recent technical developments
The revival of tram networks, particularly in France and Spain, has brought about a number of technical developments both in the traction systems and in the styling of the cars.
APS third rail
A ground-level power supply system known as Ground-level power supply or APS is an updated version of the original stud type system. APS uses a third rail placed between the running rails, divided electrically into eight-metre powered segments with three metre neutral sections between. Each tram has two power collection skates, next to which are antennas that send radio signals to energize the power rail segments as the tram passes over them. Older systems required mechanical switching systems which were susceptible to environmental problems. At any one time no more than two consecutive segments under the tram should actually be live. Wireless and solid state switching remove the mechanical problem.
The Eurotram series was developed by Socimi of Italy. It is used by Strasbourg, Milan, and Porto. The Eurotram has a modern design that makes it look almost as much like a train as a tram, and has large windows along its entire length.
The Citadis tram, flagship of the French manufacturer Alstom, enjoys an innovative design combining lighter bogies with a modular concept for carriages providing more choices in the types of windows and the number of cars and doors. The recent Citadis-Dualis, intended to run at up to 100 km/h (62 mph), is suitable for stop spacings ranging from 500 m (1,600 ft) to 5 km (3.1 mi). Dualis is a strictly modular partial low-floor car, with all doors in the low-floor sections.
A Rubber-tyred "tram" is a trolleybus which is guided by a fixed rail on the ground and uses overhead cables like a conventional tram. This can allow the vehicles to match the capacity of conventional trams and cope with gradients up to 13% due to the rubber tyres. There are two systems which use this technology: the Guided Light Transit (GLT) and Translohr. The GLT "trams" are legally considered buses as they have steering wheels and can leave the fixed rail when requirements dictate e.g. when journeying to a depot while a Translohr "tram" cannot operate without a guidance rail and are generally not considered buses.
Pivoting bogies in 100% low-floor
Most low-floor trams carry the mechanical penalty of requiring bogies to be fixed and unable to pivot. This creates undue wear on the tracks and wheels and reduces the speed at which a tram can drive through a curve. Some manufacturers such as Citadis deal with the issue by introducing partially high floor trams. Others try to overcome all shortcomings, and in 2009 the some such as the Škoda 15 T was developed with pivoting bogies at the ends and with jacobs bogies between the articulations, but this solution proved expensive.
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