A trolleybus (also known as trolley bus, trolley coach, trackless trolley, trackless tram [in early years] or trolley) is an electric bus that draws its electricity from overhead wires (generally suspended from roadside posts) using spring-loaded trolley poles. Two wires and poles are required to complete the electrical circuit. This differs from a tram or streetcar, which normally uses the track as the return part of the electrical path and therefore needs only one wire and one pole (or pantograph). They also are distinct from other kinds of electric buses, which usually rely on batteries.
Currently, around 315 trolleybus systems are in operation, in cities and towns in 45 countries. Altogether, more than 800 trolleybus systems have existed, but not more than about 400 concurrently.
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The trolleybus dates back to 29 April 1882, when Dr. Ernst Werner von Siemens ran his "Elektromote" in a Berlin suburb. This experimental demonstration continued until 13 June 1882, after which there were few developments in Europe, although separate experiments were conducted in the USA. In 1899, another vehicle which could run either on or off rails was demonstrated in Berlin. The next development was when Lombard Gérin operated an experimental line at the Paris Exhibition of 1900 after four years of trials, connecting the Exhibition with the Porte de Vincennes. Max Schiemann took the biggest step when on 10 July 1901 the world's first passenger-carrying trolleybus operated at Bielatal (Biela Valley, near Dresden), in Germany. Schiemann built and operated the Bielatal system, and is credited with developing the under-running trolley current collection system, with two horizontally parallel overhead wires and rigid trolleypoles spring-loaded to hold them up to the wires. Although this system operated only until 1904, Schiemann had developed what is now the standard trolleybus current collection system. In the early days there were a few other methods of current collection. The Cédès-Stoll (Mercédès-Électrique-Stoll) system was operated near Dresden between 1902 and 1904, and in Vienna. The Lloyd-Köhler or Bremen system was tried out in Bremen, and the Filovia was demonstrated near Milan.
Leeds and Bradford became the first cities to put trolleybuses into service in Great Britain on 20 June 1911. Bradford was also the last to operate trolleybuses in the UK, the system closing on 26 March 1972. The last rear-entrance trolleybus in Britain was also in Bradford and is now owned by the Bradford Trolleybus Association. Birmingham was the first to replace a tram route with trolleybuses, while Wolverhampton, under the direction of Charles Owen Silvers, became world-famous for its trolleybus designs. There were 50 trolleybus systems in the UK, London's being the largest. By the time trolleybuses arrived in Britain in 1911, the Schiemann system was well established and was the most common, although the Cédès-Stoll (Mercédès-Électrique-Stoll) system was tried in West Ham (in 1912) and in Keighley (in 1913).
In the U.S.A., some cities, led by the Brooklyn-Manhattan Transit Corporation (BMT—New York), subscribed to the all-four concept of using buses, trolleybuses, trams (in US called streetcars or trolleys) and rapid transit subway and/or elevated lines (metros), as appropriate, for routes ranging from the lightly used to the heaviest trunk line. Buses and trolleybuses in particular were seen as entry systems that could later be upgraded to rail as appropriate. In a similar fashion, many cities in Britain originally viewed trolleybus routes as extensions to tram (streetcar) routes where the cost of constructing or restoring track could not be justified at the time, though this attitude changed markedly (to viewing them as outright replacements for tram routes) in the years after 1918. Although the BMT in Brooklyn built only one trolleybus line, other cities, notably San Francisco (California), and Philadelphia (Pennsylvania), built larger systems and apparently still maintain an "all-four" approach to the current day. Some trolleybus lines in the United States (and in Britain, as noted above) came into existence when a trolley or tram route did not have sufficient ridership to warrant track maintenance or reconstruction. In a similar manner, a proposed tram scheme in Leeds, United Kingdom, was changed to a trolleybus scheme to cut costs.
Trolleybuses are uncommon today in North America, but they remain common in many European countries as well as Russia and China, generally occupying a position in usage between street railways (trams) and diesel buses. Worldwide, around 315 cities or metropolitan areas are served by trolleybuses today. (Further detail under Use and preservation, below.)
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Trolleybuses are advantageous on hilly routes, as electric motors are more effective than diesel engines in providing torque at start-up, an advantage for climbing steep hills. Unlike combustion engines, electric motors draw power from a central plant and can be overloaded for short periods without damage. San Francisco and Seattle, both hilly American cities, use trolleybuses partly for this reason, another being improved air quality. Given their acceleration and braking performance, trolleybuses can outperform diesel buses on flat stretches as well.
Trolleybuses' rubber tyres have better adhesion than trams' steel wheels on steel rails, giving them better hill-climbing capability and braking. Unlike rail vehicles (where side tracks are not available), an out-of-service vehicle can be moved to the side of the road and its trolley poles lowered, allowing other trolleybuses to pass. Additionally, because they are not confined to tracks, trolleybuses can pull over to the curb as a diesel bus does, eliminating boarding islands in the middle of the street.
Like other electric vehicles, trolleybuses are more environmentally friendly in the city than fossil-fuel or hydrocarbon-based vehicles (petrol/gasoline, diesel, alcohol, etc.). Although the power is not free, having to be produced at centralised power plants with attendant transmission losses, it is produced more efficiently. Further, it is not bound to a specific fuel source and is more amenable to pollution control as a point source supply than are individual vehicles with their own engines exhausting noxious gases and particulates at street level. Moreover, some cities, like Calgary, Alberta, run their light rail networks using wind energy, which is effectively emission-free once the turbines are built and installed. Other cities, Vancouver, B.C., for instance, use hydroelectricity. A further advantage of trolleybuses is that they can generate electricity from kinetic energy while braking, a process known as regenerative braking. However, for regenerative braking to work as such, there must be another bus on the same circuit that needs power, or a way to send the excess power back to the commercial electric power system. Otherwise the braking power must be dissipated in resistance grids on the bus, when it is called "dynamic braking". There are alternatives, such as batteries or flywheels on the bus or at the bus power station, but they add to the investment, complexity and maintenance expenses.
Unlike trams or gasoline and diesel buses, trolleybuses are almost silent, lacking the noise of an engine or of wheels on rails. Such noise as there is tends to emanate from auxiliary systems such as power steering pumps and air conditioning. Early trolleybuses without these systems were even quieter and, in the UK at least, were often referred to as the "Silent Service". The quietness did have its disadvantages though, with some pedestrians falling victim to what was also known as the "Silent Death" (in Britain) or "Whispering Death" (in Australia).
Trolleybuses are especially favoured where electricity is abundant and cheap. Examples are the extensive systems in Vancouver, Canada and Seattle, USA, both of which draw hydroelectric power from the Columbia River and other Pacific river systems. San Francisco operates its system using hydro power from the city-owned Hetch Hetchy generating plant.
As can be seen from examples in this article, electric (trolley) buses tend to be very long-lived as compared to internal combustion engine-powered buses. As the basic construction of buses has not changed much in the last fifty plus years, they can be upgraded such as when air conditioning was retrofitted to many trolleybuses when it became available. Wheelchair lifts are relatively simple to add; kneeling front suspension is a common feature of air suspension on the front axle in place of springs.
Trolleybuses are used extensively in large European cities, such as Athens, Belgrade, Bratislava, Bucharest, Budapest, Chisinau, Kiev, Lyon, Milan, Minsk, Moscow, Riga, Saint Petersburg, Sofia, Varna and Zurich, as well as smaller ones such as Arnhem, Bergen, Brest (Belarus), Cluj-Napoca, Coimbra, Gdynia, Kaunas, Lausanne, Limoges, Luzern, Parma, Piatra Neamţ, Plzeň, Prešov, Salzburg, Solingen, Szeged, Tallinn, Timişoara and Yalta. Realising the advantages of these zero-emission vehicles, some cities have started to expand their systems again, while others, such as Montréal, Lecce, and Leeds, plan to introduce new trolleybus systems. See also Trolleybus systems by city.
In Cambridge, Massachusetts, the trolleybus system has survived because Harvard Station, where several bus lines terminate, is in a tunnel that was once used by trams. Although diesel buses do use the tunnel, there are limitations due to exhaust fumes. Also the trolleybuses continue to have popular support.
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Re-routings, temporary or permanent, are not usually readily available outside of "downtown" areas where the buses may be re-routed via adjacent business area streets where other trolleybus routes operate. This problem was highlighted in Vancouver in July 2008, when an explosion closed several roads in the city's downtown core. Because of the closure, trolleys were forced to detour several kilometers off their route in order to stay on the wires, leaving major portions of their routes unserved and service well off schedule. Also trolley buses have unique operating characteristics, such as trolley drivers must slow down at turns and through switches in the overhead wire system.[SDOT 1]
Some trolleybus systems have been criticised for aesthetic reasons, with city residents complaining that the jumble of overhead wires was unsightly. Intersections often have a "webbed ceiling" appearance, due to multiple crossing and converging sets of trolley wires.
Dewirements — when the trolley poles come off of the wires — sometimes occur, especially in areas subject to heavy snow. After a dewirement, trolleybuses not equipped with an auxiliary power unit (APU) are stranded without power. However, dewirements are relatively rare in modern systems with well-maintained overhead wires, hangers, fittings and "contact shoes". Trolleybuses are equipped with special insulated pole ropes which drivers use to reconnect the trolley poles with the overhead wires in case of dewirement. When approaching switches, trolleybuses usually must decelerate in order to avoid dewiring, and this deceleration can potentially add slightly to traffic congestion.
Trolleybuses cannot overtake one another in regular service unless two separate sets of wires with a switch are provided or the vehicles are equipped with off-wire capability, but the latter is an increasingly common feature of new trolleybuses.
With the introduction of hybrid designs, trolleybuses are no longer tied to overhead wires. Since the 1980s, trolleybus systems in Muni in San Francisco, TransLink in Vancouver, and in Beijing, among others, have bought trolleybuses equipped with batteries to allow them to operate fairly long distances away from the wires. Supercapacitors can be also used to move buses short distances.
Trolleybuses can optionally be equipped either with limited off-wire capability—a small diesel engine or battery pack—for auxiliary or emergency use only, or full dual-mode capability. A simple auxiliary power unit can allow a trolleybus to get around a route blockage or can reduce the amount (or complexity) of overhead wiring needed at operating garages (depots). This capability has become increasingly common in newer trolleybuses, particularly in North America and Western Europe, where the vast majority of new trolleybuses delivered since the 1990s are fitted with at least limited off-wire capability. These have gradually replaced older trolleybuses which lacked such capability. In Philadelphia, new trolleybuses (known there as "trackless trolleys") that were placed in service by SEPTA in 2008 are equipped with small hybrid diesel-electric power units for operating short distances off-wire, instead of using a conventional diesel drive train or battery-only system for their off-wire movement.
King County Metro in Seattle, Washington and MBTA in Boston use or have used dual-mode buses that run on electric power from overhead wires on a fixed right-of-way and on diesel power on city streets. Metro used special-order articulated Breda buses with the center axle driven electrically and the rear (third) axle driven by a conventional power pack, with electricity used for clean operation in the downtown transit tunnel. They were introduced in 1990 and retired in 2005, replaced by cleaner hybrid buses, although 59 of 236 had their diesel propulsion equipment removed and continue (as of 2010) in trolley bus service on non-tunnel routes. MBTA uses dual-mode buses on its new (2004-opened) Silver Line (Waterfront).
With increasing diesel fuel costs and problems caused by particulate matter and NOx emissions in cities, trolleybuses can be an attractive alternative, either as the primary transit mode or as a supplement to rapid transit and commuter rail networks.
It has been suggested[by whom?] that trolleybuses will become obsolete in a future hydrogen economy, but direct electric transmission is at least twice as efficient as the alternative, viz. conversion of energy into hydrogen, transportation and storage of the hydrogen and its conversion back into electricity by fuel cells.
Being electric, trolleybuses are a lot quieter than diesel- or petrol-engined vehicles. While this is mainly seen as a benefit, it does also make it easier for unobservant pedestrians and other motorists to miss hearing a trolleybus when crossing a street and risk being struck. A speaker attached to the front of the vehicle can raise the noise to a desired "safe" level. This noise can be directed to pedestrians in front of the vehicle, as opposed to motor noise which typically comes from the rear of a bus and is more noticeable to bystanders than to pedestrians.
Trolleybuses can share overhead wires and other electrical infrastructure (such as substations) with tramways. This can result in cost savings when trolleybuses are added to a transport system that already has trams, though this refers only to potential savings over the cost of installing and operating trolleybuses alone.
Trolleybus wire switches are used where a trolleybus line branches into two or where two lines join. A switch may be either in a "straight through" or "turnout" position; it normally remains in the "straight through" position unless it has been triggered, and reverts to it after a few seconds or after the pole shoe passes through and strikes a release lever. (In Boston, the resting or "default" position is the "leftmost" position.) Triggering is typically accomplished by a pair of contacts, one on each wire close to and before the switch assembly, which power a pair of electromagnets, one in each frog with diverging wires. ("Frog" generally refers to one fitting that guides one trolley wheel/shoe onto a desired wire or across one wire. Occasionally "frog" has been used to refer to the entire switch assembly.)
Multiple branches may be handled by installing more than one switch assembly. For example, to provide straight-through, left-turn or right-turn branches at an intersection, one switch is installed some distance from the intersection to choose the wires over the left-turn lane, and another switch is mounted closer to or in the intersection to choose between straight through and a right turn. (This would be the arrangement in countries such as the US, where traffic directionality is right-handed; in left-handed traffic countries such as Britain and New Zealand, the first switch (before the intersection) would be used to access the right-turn lanes, and the second switch (usually in the intersection) would be for the left-turn.)
Three common types of switches exist: Power-on/Power-off (the picture of a switch above is of this type), Selectric, and Fahslabend.
A Power-on/Power-off switch is triggered if the trolleybus is drawing considerable power from the overhead wires, usually by accelerating, at the moment the poles pass over the contacts. (The contacts are lined up on the wires in this case.) If the trolleybus "coasts" through the switch, the switch will not activate. Some trolleybuses, such as those in Philadelphia and Vancouver, have a manual "power-coast" toggle switch that turns the power on or off. This allows a switch to be triggered in situations that would otherwise be impossible, such as activating a switch while braking or accelerating through a switch without activating it. One variation of the toggle switch will simulate accelerating by causing a larger power draw (through a resistance grid) but will not simulate coasting and prevent activation of the switch by cutting the power.
A Selectric switch has a similar design, but the contacts on the wires are skewed, often at a 45-degree angle, rather than being lined up. This skew means that a trolleybus going straight through will not trigger the switch, but a trolleybus making a turn will have its poles match the contacts in a matching skew (with one pole shoe ahead of the other), which will trigger the switch regardless of power draw (accelerating versus coasting).
For a Fahslabend switch, the trolleybus's turn indicator control (or a separate driver-controlled switch) causes a coded radio signal to be sent from a transmitter, often attached to a trolley pole. The receiver is attached to the switch and causes it to trigger if the correct code is received. This has the advantage that the driver does not need to be accelerating the bus (as with a Power-on/Power-off switch) or trying to make a sharp turn (as with a Selectric switch).
Trailing switches (where two sets of wires merge) do not require action by the operator. The frog runners are pushed into the desired position by the trolley shoe, or the frog is shaped so the shoe is guided onto the exit wire without any moving parts.
Since the end of 1997, no double-decker trolleybuses have been in service anywhere in the world, but in the past several manufacturers made such vehicles. Most builders of double-deck trolleybuses were in the United Kingdom, but there were a few, usually solitary, instances of such trolleybuses being built in other countries, including in Germany by Henschel (for Hamburg); in Italy by Lancia (for Porto, Portugal); in Russia by the Yaroslavl motor plant (for Moscow) and in Spain by Maquitrans (for Barcelona). British manufacturers of double-deck trolleybuses included AEC, BUT, Crossley, Guy, Leyland, Karrier, Sunbeam and others.
In 2001, Citybus (Hong Kong) converted a Dennis Dragon (#701) into a double-decker trolleybus, and it was tested on a 300-metre track in Wong Chuk Hang in that year. Hong Kong decided not to build a trolleybus system, and the testing of this prototype did not lead to any further production of vehicles.
There are currently around 315 cities or metropolitan areas where trolleybuses are operated, and more than 500 additional trolleybus systems have existed in the past. For an overview, by country, see Trolleybus usage by country, and for complete lists of trolleybus systems by location, with dates of opening and (where applicable) closure, see List of trolleybus systems and the related lists indexed there.
Of the systems existing as of 2010, the majority are located in Eurasia, including about 85 in Russia and more than 40 in Ukraine. However, there are eight systems existing in North America, nine in South America and one in Australasia (specifically in New Zealand).
Trolleybuses have been preserved in most of the countries where they have operated. The United Kingdom has the largest number of preserved trolleybuses with more than 110, while the United States has around 70. Most preserved vehicles are on static display only, but a few museums are equipped with a trolleybus line, allowing trolleybuses to operate for visitors. Museums with operational trolleybus routes include three in the UK – the Trolleybus Museum at Sandtoft, the East Anglia Transport Museum and the Black Country Living Museum – and three in the United States – the Illinois Railway Museum, the Seashore Trolley Museum and the Shore Line Trolley Museum – but operation of trolleybuses does not necessarily occur on a regular schedule of dates at these museums.
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