Seall an tùs aig Bus-troilidh

{{obair}}
[[File:Trolleybus Low Floor 4 1500 - Sao Paulo, Brazil.JPG|thumb|Bus-troilidh [[Busscar]] ann an [[São Paulo]], Braisil]]
[[File:Trådbuss Landskrona.JPG|thumb|Bus-troilidh [[Solaris Bus & Coach|Solaris]] ann an [[Landskrona]], an t-Suain]]
[[File:Gent trolleybus.ogg|thumb|right|Video de bhus-troilidh ann an [[Ghent]], a' Bheilg]]

Tha '''bus-troilidh'' (no '''coidse troilidh''' no '''troilidh/trama gun traca''{{Snd}}sna 1910an agus 1920an<ref name="joyce-king-newman">Joyce, J.; King, J. S.; and Newman, A. G. (1986). ''British Trolleybus Systems'', pp. 9, 12. London: [[Ian Allan Publishing]]. {{ISBN|0-7110-1647-X}}.</ref>{{Snd}} no dìreach '''troilidh'''<ref name="dunbar">Dunbar, Charles S. (1967). ''Buses, Trolleys & Trams''. Paul Hamlyn Ltd. (UK). Republished 2004 with {{ISBN|0-7537-0970-8}} or 9780753709702.</ref><ref name="vanc60">{{cite press release| title = Trolley service begins the next 60 years| publisher = [[TransLink (British Columbia)|TransLink]] |location= Vancouver |date=16 August 2008 |url= http://www.translink.ca/en/About-TransLink/Media/2008/August/Trolley-service-begins-the-next-60-years.aspx |archive-url= https://web.archive.org/web/20140201213805/http://www.translink.ca/en/About-TransLink/Media/2008/August/Trolley-service-begins-the-next-60-years.aspx| archive-date = 1 February 2014| access-date = 6 September 2012| url-status = dead}}</ref>) na [[bus-dealain|bhus-dealain]] a gheibh dealan o ùeirichean os a chionn (mar is trice crochte ri puist ri taobh an rathaid) tro chabair troilidh sa bheil spriongan. [[Overhead line#Parallel overhead lines|Two wires]], and two trolley poles, are required to complete the electrical circuit. This differs from a [[tram]] or streetcar, which normally uses the track as the return path, needing only one wire and one pole (or [[pantograph (transport)|pantograph]]). They are also distinct from other kinds of [[Battery electric bus|electric buses]], which usually rely on [[Automotive battery|batteries]]. Power is most commonly supplied as 600-[[volt]] [[direct current]], but there are exceptions.

Currently, around 300 trolleybus systems are in operation, in cities and towns in 43 countries.<ref name="janes2012">Webb, Mary (ed.) (2012). ''Jane's Urban Transport Systems 2012–2013'', pp. "[23]" and "[24]" (in foreword). Coulsdon, Surrey (UK): [[Jane's Information Group]]. {{ISBN|978-0-7106-2994-4}}.</ref> Altogether, more than 800 trolleybus systems have existed, but not more than about 400 concurrently.<ref name="Murray">Murray, Alan (2000). ''World Trolleybus Encyclopaedia''. Yateley, Hampshire, UK: Trolleybooks. {{ISBN|0-904235-18-1}}.</ref>

==History==
[[File:First Trolleybuss of Siemens in Berlin 1882 (postcard).jpg|thumb|right|The "Elektromote", the world's first trolleybus,<ref>[http://www.siemens.com/history/en/innovations/transportation.htm#toc-2 ''Elektromote''], Siemens History website on 14 August 2015</ref> in Berlin, Germany, 1882]]

The trolleybus dates back to 29 April 1882, when Dr. [[Werner von Siemens|Ernst Werner Siemens]] demonstrated his "[[Electromote|Elektromote]]" in a [[Berlin]] suburb.<ref>{{Cite journal |last1=Di̇Kmen |first1=İsmail Can |last2=Eki̇Ci̇ |first2=Yunus Emre |last3=Karadağ |first3=Teoman |last4=Abbasov |first4=Teymuraz |last5=Hamamci |first5=Serdar Ethem |date=2021-01-30 |title=Electrification in Urban Transport: A Case Study with Real-time Data |journal=Balkan Journal of Electrical and Computer Engineering |volume=9 |issue=1 |pages=69–77 |doi=10.17694/bajece.837248 |issn=2147-284X|doi-access=free }}</ref> This experiment continued until 13 June 1882, after which there were few developments in Europe, although separate experiments were conducted in the United States.<ref name="ABruce">Ashley Bruce, ''Lombard-Gerin and Inventing the Trolleybus'' (Trolleybooks, 2017, {{ISBN|978-0-904235-25-8}}), p. 88 ''et seq''.</ref> In 1899, another vehicle which could run either on or off rails was demonstrated in Berlin.<ref name="CSDunbar">Charles S. Dunbar, ''Buses, Trolleys and Trams'' (Paul Hamlyn Ltd, 1967, no ISBN), p. 81 ''et seq''.</ref> The next development was when [[Louis Lombard-Gérin]] operated an experimental line at the [[Exposition Universelle (1900)|Paris Exhibition of 1900]] after four years of trials, with a circular route around Lake Daumesnil that carried passengers. Routes followed in six places including Eberswalde and Fontainebleau.<ref name="HMartin">Henry Martin, ''Lignes Aeriennes et Trolleys pour Automobile sur Route'' (Libraire Polytechnique Ch., 1902, no ISBN), p. 29 ''et seq''.</ref> [[:de:Max Schiemann|Max Schiemann]] on 10 July 1901 opened the world's fourth passenger-carrying trolleybus system, which operated at Bielatal (Biela Valley, near [[Dresden]]), Germany. Schiemann built and operated the [[Biela Valley Trolleybus|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 many other methods of current collection.<ref name="ABruce"/> The [[Cédès-Stoll]] (Mercédès-Électrique-Stoll) system was first operated near Dresden between 1902 and 1904, and 18 systems followed. The [[Lloyd-Köhler]] or Bremen system was tried out in [[Bremen]] with 5 further installations, and the [[Cantono Frigerio system]] was used in Italy.

Throughout this period, trackless freight systems and electric canal boats were also built.

[[File:Reading Trolleybus at Three Tuns.jpg|thumb|A double-deck trolleybus in [[Trolleybuses in Reading|Reading]], England, 1966]]
[[Leeds]] and [[Bradford]] became the first cities to put trolleybuses into service in Great Britain, on 20 June 1911.<ref name="CSDunbar"/> Supposedly, though it was opened on 20 June, the public was not admitted to the Bradford route until the 24th. Bradford was also the last city to operate trolleybuses in the UK; the system closed on 26 March 1972. The last rear-entrance trolleybus in service in Britain was also in Bradford and is now owned by the [[Trolleybuses in Bradford|Bradford Trolleybus Association]]. [[Birmingham]] was the first UK city to replace a tram route with trolleybuses, while [[Wolverhampton]], under the direction of Charles Owen Silvers, became world-famous for its trolleybus designs.<ref>Dunbar p. 84</ref> 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).<ref>Dunbar p. 83</ref><ref name="King">J. S. King, ''Keighley Corporation Transport'', (Advertiser Press Ltd, 1964, no ISBN) p. 39 ''et seq''.</ref>

Smaller trackless trolley systems were built in the US early as well. The first non-experimental system was a seasonal municipal line installed near [[Hull, MA|Nantasket Beach]] in 1904; the first year-round commercial line was built to open a hilly property to development just outside [[Los Angeles]] in 1910. The trackless trolley was often seen as an interim step, leading to [[tram|streetcars]]. In the US, some systems subscribed to the all-four concept of using buses, trolleybuses, streetcars (''trams, 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.<ref>Dunbar, p. 90</ref> Trackless trolleys were the dominant form of new post-World War I [[Railway electrification|electric traction]], with extensive systems in among others, Los Angeles, [[Chicago]], [[United Electric Railways|Rhode Island]], and [[Trolleybuses in Atlanta|Atlanta]]; [[Trolleybuses in Greater Boston|Boston]], [[Trolleybuses in San Francisco|San Francisco]], and [[Trolleybuses in Philadelphia|Philadelphia]] still maintain an "all-four" fleet.
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.<ref>{{cite news
  | title = Plan for city trolleybus comeback
  | work = BBC News
  | date = 15 June 2007
| url= http://news.bbc.co.uk/2/hi/uk_news/england/west_yorkshire/6755469.stm
  | access-date=3 June 2009
}}</ref>

[[File:СМЕ из ЗиУ-9 в Ленинграде.jpg|thumb|250px|[[Multiple-unit train control|MU]] [[ZiU-9]] in Soviet Union, 1987]]
Trolleybuses are uncommon today in North America, but their use is widespread in Europe and Russia. They remain common in many countries which were part of the [[Soviet Union]].<ref>{{Cite web|title=Trolley with an internal combustion engine. Electric cars of the USSR. Excerpt of a Cargo Trolley Bus|url=https://gtshina.ru/en/uluchsheniya-v-salone/trolleibus-s-dvigatelem-vnutrennego-sgoraniya-elektromobili-sssr/|access-date=20 October 2020|website=gtshina.ru}}</ref> Generally trolleybuses occupy a position in usage between street railways (trams) and motorbuses. Worldwide, around 300 cities or metropolitan areas on 5 continents are served by trolleybuses (further detail under [[#Use and preservation|Use and preservation]], below).

<!-- Do not add cities to this list. It is intended to be only a list of examples, not a complete list (other Wikipedia articles exist for that purpose), and it should not include more than 1 city per country except for countries with many trolleybus systems (and still should not include more than 2 per country). -->[[File:沪A57050D 20.jpg|thumb|The Shanghai trolleybus system is currently the oldest in the world.]]
[[File:WYMT 34980 leaving Wuyang Community (20240326134517).jpg|thumb|Some [[coal mining|coal mines]] also operate separate trolleybus systems to serve workers. Wuyang Coal Mine in [[Xiangyuan County|Xiangyuan]], [[Changzhi]], [[Shanxi]] has the last remaining mine trolleybus system in China.]]
This mode of transport operates in large cities, such as [[Trolleybuses in Belgrade|Belgrade]], [[Trolleybuses in Lyon|Lyon]], [[Trolleybuses in Pyongyang|Pyongyang]], [[Trolleybuses in São Paulo|São Paulo]], [[Trolleybuses in Seattle|Seattle]], [[Trolleybuses in Sofia|Sofia]], [[Saint Petersburg|St. Petersburg]], and [[Trolleybuses in Zürich|Zurich]], as well as in smaller ones such as [[Trolleybuses in Dayton|Dayton]], [[Trolleybuses in Gdynia|Gdynia]], [[Trolleybuses in Lausanne|Lausanne]], [[Trolleybuses in Limoges|Limoges]], [[Trolleybuses in Modena|Modena]], and [[Trolleybuses in Salzburg|Salzburg]]. As of 2020, [[Trolleybuses in Kyiv|Kyiv]] has, due to its history in the former Soviet Union, the largest trolleybus system in the world in terms of route length while another formerly Soviet city, [[Trolleybuses in Minsk|Minsk]], has the largest system in terms of number of routes (which also date back to the Soviet era).<ref>{{Cite web|title=Transport in Kiev, Ukraine|url=https://www.classicbuses.co.uk/kiev.html|access-date=20 October 2020|website=www.classicbuses.co.uk}}</ref> [[Landskrona]] has the smallest system in terms of route length, while [[Mariánské Lázně]] is the smallest city to be served by trolleybuses. Opened in 1914, [[Trolleybuses in Shanghai|Shanghai's trolleybus system]] is the oldest operating system in the world. With a length of 86&nbsp;km, route #52 of [[Crimean Trolleybus]] is the longest trolleybus line in the world. ''See also [[Trolleybus usage by country]].''

Transit authorities in some cities have reduced or discontinued the use of trolleybuses in recent years, while others, wanting to add or expand use of [[Zero-emissions vehicle|zero-emission vehicles]] in an urban environment, have opened new systems or are planning new systems. For example, new systems opened in [[Trolleybuses in Lecce|Lecce]], Italy, in 2012; in [[Malatya]], Turkey, in 2015;<ref name="tm321p90">''Trolleybus Magazine'' No. 321 (May–June 2015), p. 90.</ref> and in [[BRT Marrakesh|Marrakesh]], Morocco, in 2017.<ref name="RGI-2017sep">{{cite news|url=https://www.railwaygazette.com/projects-and-planning/marrakech-trolleybus-route-inaugurated/45245.article |title=Marrakech trolleybus route inaugurated 
|magazine=[[Metro Report International]] |publisher=Railway Gazette International |archive-url=https://web.archive.org/web/20200619234203/https://www.railwaygazette.com/projects-and-planning/marrakech-trolleybus-route-inaugurated/45245.article |archive-date=19 June 2020 |url-status=live}}</ref> [[Beijing Bus|Beijing]] and [[Trolleybuses in Shanghai|Shanghai]] have been expanding their respective systems, with Beijing expanding to a 31-line system operated with a fleet of over 1,250 trolleybuses.<ref>{{Cite web|url=http://www.xinhuanet.com/local/2020-01/15/c_1125462807.htm|archive-url=https://web.archive.org/web/20200116183217/http://www.xinhuanet.com/local/2020-01/15/c_1125462807.htm|url-status=dead|archive-date=16 January 2020|title=北京多措并举治理PM2.5 一微克一微克往下抠-新华网|website=www.xinhuanet.com|access-date=14 March 2020}}</ref> Trolleybuses have been long encouraged in North Korea with the newest city to have a network being [[Manpo]] in December 2019.<ref>{{Cite web|url=http://www.pyongyangtimes.com.kp/?bbs=34493|access-date=2 September 2021|website=www.pyongyangtimes.com.kp|title=PyongyangTimes &#124; home }}</ref> Since the year 2022, the city of Prague is constructing a new trolleybus system.<ref>{{cite web | url=https://www.praguemorning.cz/trolleybuses-are-back-to-prague-after-50-years/ | title=Trolleybuses Are Back to Prague After 50 Years | date=15 October 2022 }}</ref> Meanwhile, in 2023, plans for a trolleybus line in Berlin were scrapped in favour of a solution with battery-powered vehicles.<ref name="berlinaus"/>

==Vehicle design==
{|
|-
| [[File:Trolleybus diagram-key.svg|thumb|left|upright=2.25|Diagram of a 1947-built Pullman Standard model 800 trolleybus, a type still running in [[Trolleybuses in Valparaíso|Valparaíso]] (Chile)]]
|
# [[Overhead line#Parallel overhead lines|Parallel overhead lines]] (overhead wires)
# [[Destination sign|Destination or route sign]]
# [[Rear view mirror]]
# [[Headlight]]s
# Boarding (entry) doors
# Direction (turning) wheels <!-- Needs an article -->
# Exit doors<!-- Needs an article -->
# [[Traction wheel]]s
# Decorative elements
# Retractors/retrievers <!-- Needs an article -->
# Pole rope
# [[Contact shoe]]s
# [[Trolley pole]]s ([[power collector]])
# Pole storage hooks
# Trolley pole base and fairing/shroud
# Bus number
|}

Modern design vehicles
<gallery mode="packed">
File:Irisbus Cristalis ETB 12 n°115 TCL Place Carnot.jpg|Irisbus Cristalis in [[Limoges]]
File:Parma - TEP - Van Hool Exquicity 18 T.jpg|Van Hool Exquicity 18T in [[Parma]]
File:AKCM-420 in Minsk - 04.jpg|AKSM-420 Vitovt in [[Minsk]]
File:King County Metro XT60 trolleybus 4507 on Broadway (2016).jpg|New Flyer XT60 in [[Trolleybuses in Seattle|Seattle]]
File:9525493 at Gulou (20240405122447).jpg|Youngman JNP6183BEV in [[Beijing]]
File:12-11-02-bus-am-bahnhof-salzburg-by-RalfR-24.jpg|Solaris Trollino 18 in [[Salzburg]]
File:Trolebus-Castellon-300416.jpg|Trolleybus in [[Castellón de la Plana]]
File:Malatya trolleybus 4403 at Bugday Pazari in 2017.jpg|Trolleybus in [[Malatya]]
</gallery>
<!--Riyadh campus trolley wanted-->

==Advantages==
{{More citations needed section|date=May 2010}}
[[File:San Francisco Nob Hill 2.jpg|thumb|A [[San Francisco Municipal Railway|San Francisco Muni]] trolleybus ([[Electric Transit, Inc.|ETI]] 14TrSF) climbing [[Nob Hill, San Francisco|Nob Hill]]]]

===Comparison to trams===
*Cheaper infrastructure{{snd}}The initial start up cost of [[tram]]s is much higher, due to rail, signals, and other infrastructure. Trolleybuses can pull over to the kerb like other buses, eliminating the need for special boarding stations or boarding islands in the middle of the street, thus stations can be moved as needed.
*Better hill climbing{{snd}}Trolleybuses' [[rubber]] tyres have better [[adhesion]] than trams' steel wheels on steel rails, giving them better hill-climbing capability and braking.
*Easier traffic avoidance{{snd}}Unlike trams (where side tracks are often unavailable), an out-of-service vehicle can be moved to the side of the road and its trolley poles lowered. The ability to drive a substantial distance from the power wires allows trackless vehicles to avoid obstacles, although it also means a possibility that the vehicle may steer or skid far enough that the trolley pole can no longer reach the wire, stranding the vehicle. Trackless trolleys also are able to avoid collisions by manoeuvring around obstacles, similar to [[bus|motor buses]] and other road vehicles, while trams can only change speed.
*Quietness{{snd}}Trolleybuses are generally quieter than trams.
*Easier training{{snd}}The control of trolleybuses is relatively similar to motorbuses; the potential operator pool for all buses is much larger than for trams.

===Comparison to motorbuses===
[[File:Tateyama tunnel trolley bus 01.jpg|thumb|right|Trolleybus on [[Tateyama Tunnel Trolleybus|tunnel line]] in [[Tateyama, Toyama|Tateyama]]]]
[[File:Kurobe Dam station platform.jpg|thumb|right|[[Kanden Tunnel Electric Bus|Underground trolleybus]] at [[Kurobe Dam Station]]]]
{{Unordered list
|Better hill climbing{{snd}}Trolleybuses are better than motorbuses on hilly routes, as [[electric motor]]s provide much higher [[torque|static torque]] at start-up, an advantage for climbing steep hills. Unlike [[internal 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. Given their acceleration and braking performance, trolleybuses can outperform diesel [[bus]]es on flat stretches as well, which makes them better for routes that have frequent stops.
|Environmentally friendly{{snd}}Trolleybuses are usually more environmentally friendly in the city than [[fossil fuel]] or [[hydrocarbon]]-based vehicles ([[Gasoline|petrol/gasoline]], [[Diesel fuel|diesel]], [[ethanol|alcohol]], etc.). Power from a centralized [[power plant|plant]], even taking into account [[Electric power transmission#Losses|transmission losses]], is often produced more efficiently, is not bound to a specific fuel source, and is more amenable to pollution control as a [[point source (pollution)|point source]], unlike individual vehicles with exhaust gases and [[particulate]]s at street level. Trolleybuses are especially favoured where electricity is abundant, cheap, and renewable, such as hydroelectric. Systems in [[Seattle]] and in [[Vancouver]], [[British Columbia|BC]], draw [[hydroelectric]] power from the [[Columbia River]] and other [[Continental Divide of the Northern Americas#Triple points|Pacific river systems]]. [[San Francisco]] operates its system using hydro power from the city-owned [[Hetch Hetchy Reservoir|Hetch Hetchy]] generating plant.
|Trolleybuses can generate electricity from [[kinetic energy]] while braking, a process known as [[regenerative braking]]. For regenerative braking to function, there must be another bus on the same circuit needing power, an electric storage system on the vehicle or the wire system, or a method to send the excess power back to the commercial electric power system. Otherwise the braking energy must be dissipated in resistance grids on the bus; this is called "[[dynamic braking]]". The use of trolley buses also eliminates pollution during idling, thus improving air quality.
|Minimal noise pollution{{snd}}Unlike trams or gasoline and diesel buses, trolleybuses are almost silent, lacking the noise of a combustion engine or wheels on rails. Most noise comes from auxiliary systems such as [[power steering]] pumps and air conditioning. Early trolleybuses without these systems were even quieter and in the [[United Kingdom]] were sometimes referred to as the "Silent Service". This however can also be seen as a disadvantage, with some pedestrians falling victim to what was known as "Silent Death" (in Britain) or "Whispering Death" (in Australia).{{citation needed|date=August 2016}}
|Usable in enclosed space{{snd}}The absence of exhaust gases allows trolleybuses to operate underground. In [[Cambridge, Massachusetts]], trackless trolleys survived because [[Harvard (MBTA station)|Harvard Station]], where several bus lines terminate, is in a tunnel once used by streetcars. Although diesel buses do use the tunnel, there are limitations due to exhaust fumes, which running the trolleybuses through aids in ventilation. Also, the trackless trolleys continue to have popular support. The only trolleybus systems in Japan, the [[Tateyama Tunnel Trolleybus]] and [[Kanden Tunnel Trolleybus]] lines, both run in tunnels serving the [[Kurobe Dam]] and [[Tateyama Kurobe Alpine Route]], and were converted from normal diesel buses specifically for their lack of exhaust.
|Longevity and maintenance{{snd}}Electric motors typically last longer than internal combustion motors, and cause less secondary damage from vibration, so electric buses tend to be very long-lived compared to [[motorbus]]es. As the basic construction of buses has not changed much in the last 50 plus years, they can be upgraded such as when air conditioning was retrofitted to many trolleybuses. Such upgrades are often disproportionately expensive. [[Wheelchair lifts]] are relatively simple to add; [[kneeling front suspension]] is a common feature of air suspension on the front axle in lieu of springs. In comparison to battery-powered buses, the lack of a specially designed battery or fuel cell (typically with expensive patents) decreases the price and weight, and in locations with a sufficient power delivery network, the trolleybus is cheaper and easier to maintain in comparison to those requiring charging stations.{{dubious|This is dependent entirely on usage profile.|date=August 2016}}
}}

[[File:Bucharest DAC 217E articulated trolleybus 7409 in Apr 2007.jpg|thumb|A [[Rocar DAC]] 217E [[Articulated bus|articulated]] trolleybus in Bucharest, Romania, in April 2007]]
[[File:TrollyHeadworks5875.JPG|thumb|Pole bases with springs and pneumatic pole lowering cylinders]]
[[File:TrollyRopes5874.JPG|thumb|Insulated poles, contact shoes, and pull&ndash;ropes]]

==Disadvantages==
===Comparison to trams===
''Note: As there are numerous variations of tram and [[Light rail|light-rail]] technology, the disadvantages listed may be applicable only with a specific technology or design.''

*Like any bus, much less capacity than trams.
*More control required{{snd}}Trolleybuses must be driven like motorbuses, requiring directional control by the driver.
*Higher rolling resistance{{snd}}Rubber-tired vehicles generally have more [[rolling resistance]] than steel wheels, which decreases energy efficiency.
*Less efficient use of right-of-way{{snd}}Lanes must be wider for unguided buses than for streetcars, since unguided buses can drift side-to-side. The use of guidance rail allows trams running in parallel lanes to pass closer together than drivers could safely steer.
*Difficulties with platform loading{{snd}}Implementation of level platform loading with [[platform gap|minimal gap]], either at design stage or afterwards, is easier and cheaper to implement with rail vehicles.
*Wear of rubber tires leads to significant [[rubber pollution]].

===Comparison to motorbuses===
*Difficult to re-route{{snd}}When compared to [[Bus|motorbuses]], trolleybuses have greater difficulties with temporary or permanent re-routings, wiring for which is 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,<ref>{{cite news |title=Power in downtown Vancouver won't be fully restored until Tuesday |url=http://www.cbc.ca/news/canada/british-columbia/power-in-downtown-vancouver-won-t-be-fully-restored-until-tuesday-1.739479 |agency=CBC News |date=14 July 2008}} Other reports stated that the (electrical) explosion did not affect power supply to the trolleybuses (only implied by this article).</ref> when an explosion closed several roads in the city's downtown core. Because of the closure, trolleys were forced to detour several miles off their route in order to stay on the wires, leaving major portions of their routes not in service and off-schedule.
*Aesthetics{{snd}}The jumble of [[overhead line|overhead wires]] may be seen as unsightly.<ref>{{cite web|author=Ashley Bruce |url=http://www.tbus.org.uk/overhead.htm |title=Overhead |publisher=Tbus.org.uk |access-date=29 November 2010}}</ref> Intersections often have a "webbed ceiling" appearance, due to multiple crossing and converging sets of trolley wires.
*Dewirements{{snd}}[[Trolley pole]]s sometimes come off the wire. 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. When approaching switches, trolleybuses usually must decelerate in order to avoid dewiring, and this deceleration can potentially add slightly to traffic congestion. In 1998, a [[1998 Shenyang trolleybus electrocution accident|dewirement in Shenyang]] on poorly maintained infrastructure killed 5 people and ultimately led to the destruction of the trolleybus network.<ref>{{Cite web|title=沈阳1999年"电改汽"的真正原因_沈阳公交网|url=http://www.shenyangbus.com/a/gjls/2010/0614/255.html|access-date=2 September 2021|website=www.shenyangbus.com}}</ref>
*Unable to overtake other trolleybuses{{snd}}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, with the latter an increasingly common feature of new trolleybuses.
*Higher capital cost of equipment{{snd}}Trolleybuses are often long-lived equipment, with limited market demand. This generally leads to higher prices relative to [[Internal combustion engine|internal combustion]] buses. The long equipment life may also complicate upgrades.
*More training required{{snd}}Drivers must learn how to prevent dewiring, slowing down at turns and through switches in the overhead wire system, for example.<ref>{{cite web|title=Electric Trolley Bus Fact Sheet|url=http://www.seattle.gov/transportation/docs/ElectricTrolleyBusFactSheet0110.pdf|publisher=Seattle Department of Transportation|access-date=29 March 2012|url-status=dead|archive-url=https://web.archive.org/web/20170217035300/http://www.seattle.gov/transportation/docs/ElectricTrolleyBusFactSheet0110.pdf|archive-date=17 February 2017}}</ref>
*Overhead wires create obstruction{{snd}}Trolleybus systems employ overhead wires above the roads, often shared with other vehicles. The wires can restrict tall motor vehicles such as delivery trucks ("[[Truck|lorries]]") and double decker buses from using or crossing roads fitted with overhead wires, as such vehicles would hit the wires or pass dangerously close to them, risking damage and [[Electric arc|dangerous electrical faults]]. The wires also may impede positioning of overhead signage and create a hazard to activities such as road repairs using tall excavators or piling rigs, use of scaffolding, etc.

==Off-wire power developments==
[[File:Trolleybus Driver Adjusting Trolley Pole (cropped).jpg|thumb|left|On this [[articulated bus|articulated]] [[Beijing Bus|Beijing trolleybus]], the operator uses ropes to guide the trolley poles to contact the overhead wires.]]
With the re-introduction of hybrid designs, trolleybuses are no longer tied to overhead wires. The [[Transport of New Jersey|Public Service Company of New Jersey]], with [[Yellow Coach Manufacturing Company|Yellow Coach]], developed "All Service Vehicles"; trackless trolleys capable of operating as gas-electric buses when off wire, and used them successfully between 1935 and 1948. Since the 1980s, systems such as [[San Francisco Municipal Railway|Muni]] in San Francisco, [[TransLink (British Columbia)|TransLink]] in Vancouver, and [[Beijing]], among others, have bought trolleybuses equipped with batteries to allow them to operate fairly long distances away from the wires. [[Supercapacitor]]s can be also used to move buses short distances.

Trolleybuses can optionally be equipped either with limited off-wire capability&mdash;a small diesel engine or battery pack&mdash;for auxiliary or emergency use only, or full [[dual-mode bus|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 China, North America and 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 trackless trolleys equipped with small [[Hybrid electric vehicle|hybrid]] diesel-electric power units for operating short distances off-wire were placed in service by [[SEPTA]] in 2008. This is instead of the trolleys using a conventional diesel drive train or battery-only system for their off-wire movement.<ref>''Trolleybus Magazine'' No. 267 (May–June 2006), p. 71. National Trolleybus Assn. (UK).</ref>

[[File:Breda dual-mode bus at Westlake station in Downtown Seattle Transit Tunnel, 9-17-1990.jpg|thumb|right|A [[dual-mode bus]] operating as a trolleybus in the [[Downtown Seattle Transit Tunnel]], in 1990]]
[[File:Брестский троллейбус.jpg|thumb|Trolleybus with battery pack and full [[Dual-mode bus|dual-mode capability]] on the streets of [[Brest, Belarus]]]]
[[King County Metro]] in [[Seattle|Seattle, Washington]] and the [[Massachusetts Bay Transportation Authority|MBTA]] in [[Boston]]'s [[Silver Line (MBTA)|Silver Line]] have used [[dual-mode bus]]es that run on electric power from overhead wires on a fixed right-of-way and on [[Diesel engine|diesel]] power on city streets. Metro used special-order articulated [[Società Italiana Ernesto Breda|Breda]] buses, introduced in 1990, and most were retired in 2005. A limited number of the Breda dual-mode buses had their diesel engines removed, and operated exclusively as trolleybuses until 2016.<ref>{{Cite web |last=Koch |first=John |date=2016-10-28 |title=Farewell to Metro's Breda trolleys |url=https://kingcountymetro.blog/2016/10/28/farewell-to-metros-breda-trolleys/ |accessdate=2023-01-26 |work=Metro Matters Blog}}</ref> Since 2004, the MBTA has used dual-mode buses on its [[Silver Line (MBTA)|Silver Line (Waterfront)]] route. The last of these were be replaced by [[hybrid electric bus|diesel hybrid]] and [[Battery electric bus|battery-electric buses]] in June 2023.<ref>{{cite web |title=NETransit: MBTA Vehicle Inventory Main Page |url=http://www.transithistory.org/roster/ |website=roster.transithistory.org |access-date=17 January 2024}}</ref>

With the development of battery technology in recent years, trolleybuses with extended off-wire capability through on-board batteries are becoming popular. The on-board battery is charged while the vehicle is in motion under the overhead wires and then allows off-wire travel for significant distances, often in excess of 15&nbsp;km.<ref name=":0">{{Cite web|title=上海无轨电车"复兴":全换成新型辫子车 车辆增加两倍-无轨电车 辫子 高油价时代 混搭 上海公交-上海频道-东方网|url=http://sh.eastday.com/m/20140626/u1a8178158.html|access-date=6 June 2020|website=sh.eastday.com|language=zh}}</ref><ref name=":1" /> Such trolleybuses are called, among others, trolleybuses with In-Motion Charging, hybrid trolleybuses, battery trolleybuses and electric buses with dynamic charging. The main advantages of this technology over conventional battery electric buses are reduced cost and weight of the battery due to its smaller size, no delays for charging at end stops as the vehicle charges while in motion and reduced need for dedicated charging stations that take up public space. This new development allows the extension of trolleybus routes or the electrification of bus routes without the need to build overhead wires along the whole length of the route. Cities that utilize such trolleybuses include [[Beijing Bus|Beijing]],<ref>{{Cite web|last=Wong|first=Marcus|date=5 February 2019|title=Battery powered trolleybuses in Beijing|url=https://www.checkerboardhill.com/2019/02/battery-powered-trolleybuses-in-beijing/|access-date=6 June 2020|website=Checkerboard Hill|language=en-US}}</ref> [[Ostrava]],<ref name=":1">{{cite web |url=https://www.urban-transport-magazine.com/en/hybrid-trolleybuses-in-the-czech-republic/ |title=Hybrid trolleybuses in the Czech Republic |author=Martin Harák |date=13 October 2019 |website=Urban Transport Magazine}}</ref> [[Trolleybuses in Shanghai|Shanghai]],<ref name=":0" /> [[Trolleybuses in Mexico City|Mexico City]],<ref>{{Cite web|last=Mario|date=11 May 2020|title=Yutong: the Chinese leader on worldwide expansion (as electric buses gain ground)|url=https://www.sustainable-bus.com/news/yutong-bus-zhengzhou-electric-bus/|access-date=6 June 2020|website=Sustainable Bus|language=en-US}}</ref> [[Saint Petersburg]],<ref>{{Cite web|title=THE INNOVATIVE TROLLEYBUS: IN MOTION CHARGING IN NEW KNOWLEDGE BRIEF|url=https://www.uitp.org/news/innovative-trolleybus-motion-charging-new-knowledge-brief}}</ref> and [[Trolleybuses in Bergen|Bergen]].<ref>{{Cite news|last=T|first=Tom|date=25 September 2020|title=De nye Solaris trolleybussene er kommet til Bergen|url=https://bussmagasinet.no/de-nye-solaris-trolleybussene-er-kommet-til-bergen/|access-date=6 December 2021|website=Bussmagasinet|language=nb-NO}}</ref> The new trolleybus systems in [[Marrakesh]], [[Baoding]]<ref>{{Cite web|title=我市第一批双源无轨电车来啦十大亮点抢先看|url=https://mp.weixin.qq.com/s/Db2e3UKcIqDAlvi0fOrxEQ|language=zh}}</ref> and [[Prague]] are based exclusively on battery trolleybuses. In 2020, the city of [[Berlin]], Germany announced plans to build a new trolleybus system with 15 routes and 190 battery trolleybuses.<ref>{{cite web |url=https://www.urban-transport-magazine.com/en/bvg-berlin-plans-implementation-of-hybrid-trolleybuses/ |title=BVG Berlin plans implementation of hybrid trolleybuses |author=<!--Not stated--> |date=3 March 2020 |website=Urban Transport Magazine}}</ref> However, in early 2023 it was announced that the planned lines would use battery powered electric buses instead.<ref name="berlinaus">{{cite news |last=Neumann |first=Peter |date=23 January 2023 |title=Aus für die Strippe: Durch Berlin werden keine O-Busse mehr fahren |trans-title=End of the wire: There won't be trolleybuses going through Berlin |url=https://www.berliner-zeitung.de/mensch-metropole/verkehr-senat-bvg-projekt-oberleitungsbus-in-aller-stille-beerdigt-aus-fuer-die-strippe-durch-berlin-werden-keine-o-busse-mehr-fahren-li.310007 |language=German |work=Berliner Zeitung |location=Berlin |access-date=30 July 2023}}</ref>

==Other considerations==

With increasing diesel fuel costs and problems caused by particulate matter and [[NOx|NO<sub>x</sub>]] 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.

Trolleybuses are quieter than internal combustion engine vehicles. Mainly a benefit, it also provides much less warning of a trolleybus's approach. 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 [[Traction substation|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.

== The two parallel wires ==
The wires are attached to poles next to the street and carefully stretched and mounted so that they are the same width apart and same height over the road (usually about 18 to 20 feet (~5.7m)). The pair of wires is insulated from the poles and provides about 500 to 600 volts to the bus below.<ref>{{Cite web |title=Ask an Expert: Trolly bus |url=https://www.sciencebuddies.org/science-fair-projects/ask-an-expert/viewtopic.php?t=15598 |access-date=2023-10-13 |website=www.sciencebuddies.org}}</ref>

==Wire switches==
[[File:Trolley3WireSwitch.jpg|thumb|left|Trolleybus wire switch (Type Soviet Union)]]
[[File:Catenaryswitch.jpg|thumb|A switch in parallel overhead lines<ref>{{cite web |author=G. Cebrat |url=http://www.greenfleet.info |title=Greenfleet |publisher=Greenfleet.info |access-date=29 November 2010 |url-status=dead |archive-url=https://web.archive.org/web/20060212203153/http://www.greenfleet.info/ |archive-date=12 February 2006 }}</ref>]]
Trolleybus wire switches (called "frogs" in the UK) 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 [[electromagnet]]s, one in each frog with diverging wires ("frog" generally refers to one fitting that guides one [[Current collector|trolley wheel]]/[[Current collector|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<ref name="transport2000">{{cite web |archive-url=https://web.archive.org/web/20060303075510/http://www.vcn.bc.ca/t2000bc/learning/etb/electric_vehicles.html |archive-date=3 March 2006 |url-status=dead |title=Electric Vehicle Technologies |publisher=[[Transport 2000 Canada|Transport 2000 BC]] |url=http://www.vcn.bc.ca/t2000bc/learning/etb/electric_vehicles.html }}</ref> (this would be the arrangement in countries such as the United States, where [[Left- and right-hand traffic|traffic directionality]] is right-handed; in left-handed traffic countries such as the United Kingdom 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<ref name="transport2000"/> 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<ref>Trademark of Ohio Brass Co., maker of trolley wire fittings and equipment and trolley poles. The typewriter from IBM bearing that name had not been invented yet.</ref> 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' 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.

==Manufacturing==
{{Further|List of trolleybus manufacturers}}
[[File:ZiU 9 Athens.jpg|thumb|A [[ZiU-9]] trolleybus in service in [[Piraeus]], Greece, on the large Athens-area trolleybus system. The Russian-built ZiU-9 (also known as the ZiU-682), introduced in 1972, is the most numerous trolleybus model in history, with more than 45,000 built.<ref name="Murray"/>{{rp|114}} In the 2000s it was effectively rendered obsolete by [[low-floor bus|low-floor]] designs.]]
Well over 200 different trolleybus makers have existed – mostly commercial manufacturers, but in some cases (particularly in [[Communist state|communist countries]]), built by the publicly owned operating companies or authorities.<ref name="Murray"/>{{rp|91–125}} Of the defunct or former trolleybus manufacturers, the largest producers in North America and Western Europe&nbsp;– ones whose production totalled more than 1,000 units each&nbsp;– included the U.S. companies [[J. G. Brill Company|Brill]] (approx. 3,250 total), [[Pullman Company|Pullman-Standard]] (2,007), and [[Marmon-Herrington]] (1,624); the English companies [[Associated Equipment Company|AEC]] (approx. 1,750), [[British United Traction|British United Traction (BUT)]] (1,573), [[Leyland Motors|Leyland]] (1,420) and [[Sunbeam Commercial Vehicles|Sunbeam]] (1,379); France's [[Vétra]] (more than 1,750); and the Italian builders [[Alfa Romeo]] (2,044) and [[Fiat]] (approx. 1,700).<ref name="Murray"/> The largest former trolleybus manufacture is [[Trolza]] (formerly Uritsky, or ZiU) since 1951, until they declared their bankruptcy in 2017, building over 65000 trolleybuses. Also, [[Canadian Car and Foundry]] built 1,114 trolleybuses based on designs by Brill.<ref name="Murray"/>

As of the 2010s, at least 30 trolleybus manufacturers exist. They include companies that have been building trolleybuses for several decades, such as [[Škoda Works|Škoda]] since 1936 and [[New Flyer]], among others, along with several younger companies. Current trolleybus manufacturers in western and central Europe include [[Solaris Bus & Coach|Solaris]], [[Van Hool]], and [[Carrosserie Hess|Hess]], among others. In Russia ZiU/Trolza has historically been the world's largest trolleybus manufacturer, producing over 65,000 since 1951, mostly for Russia/CIS countries, but after its bankruptcy, its facilities were partially loaned out to [[PC Transport Systems]]. Škoda is Western and Central Europe's largest and the second largest in the world, having produced over 14,000 trolleybuses since 1936, mostly for export, and it also supplies trolleybus electrical equipment for other bus builders such as Solaris, SOR and Breda. In Mexico, trolleybus production ended when [[MASA (company)|MASA]], which had built more than 860 trolleybuses since 1979, was acquired in 1998 by Volvo. However, [[DINA S.A.|Dina]], which is now that country's largest bus and truck manufacturer, began building trolleybuses in 2013.<ref name="tm311">''Trolleybus Magazine'' No. 311 (September–October 2013).</ref>{{rp|134}}

==Transition to low-floor designs==
A significant change to trolleybus designs starting in the early 1990s was the introduction of [[low-floor]] models, which began only a few years after the first such models were introduced for [[motorbus]]es. These have gradually replaced [[high-floor]] designs, and by 2012, every existing trolleybus system in Western Europe had purchased low-floor trolleybuses, with the [[Trolleybuses in La Spezia|La Spezia (Italy) system]] being the last one to do so,<ref name="tm305-p119">''Trolleybus Magazine'' No. 305 (September–October 2012), p. 119.</ref> and several systems in other parts of the world have purchased low-floor vehicles.

In the United States, some transit agencies had already begun to accommodate persons in [[wheelchair]]s by purchasing buses with [[wheelchair lift]]s, and early examples of fleets of lift-equipped trolleybuses included 109 [[AM General]] trolleybuses built for the [[Trolleybuses in Seattle|Seattle trolleybus system]] in 1979 and the retrofitting of lifts in 1983 to 64 [[New Flyer|Flyer]] E800s in the [[Trolleybuses in Dayton|Dayton system]]'s fleet.<ref name="dearmond-tm141">DeArmond, R. C. (May–June 1985). "The Trolleybus System of Dayton, part 2". ''Trolleybus Magazine'' No. 141, pp. 49–64.</ref>{{rp|61}} The [[Americans with Disabilities Act of 1990]] required that all new transit vehicles placed into service after 1&nbsp;July 1993 be accessible to such passengers.<ref name="getting on board">"Getting on board" (July–August 1993). ''Trolleybus Magazine'' No. 190, pp. 86–87. National Trolleybus Association (UK).</ref>
[[File:NAW 705.jpg|thumb|One of the NAW/Hess [[Articulated bus|articulated]] trolleybuses delivered to Geneva in 1992, which were among the first production-series low-floor trolleybuses]]

Trolleybuses in other countries also began to introduce better access for the disabled in the 1990s, when the first two low-floor trolleybus models were introduced in Europe, both built in 1991, a "Swisstrolley" demonstrator built by Switzerland's [[Nutzfahrzeuggesellschaft Arbon & Wetzikon|NAW]]/[[Carrosserie Hess|Hess]] and an N6020 demonstrator built by [[Neoplan]].<ref name="tm179-p100">''Trolleybus Magazine'' No. 179 (September–October 1991), pp. 100–101.</ref><ref name=N6020>"The Neoplan N6020 Low-Floor Trolleybus". ''Trolleybus Magazine'' No. 183 (May–June 1992), p. 68.</ref> The first production-series low-floor trolleybuses were built in 1992: 13 by NAW for the [[Trolleybuses in Geneva|Geneva system]] and 10 [[Gräf & Stift]] for the {{Interlanguage link|Trolleybuses in Innsbruck|de|3=Oberleitungsbus Innsbruck|lt=Innsbruck system}}. By 1995, such vehicles were also being made by several other European manufacturers, including [[Škoda Works|Skoda]], [[Società Italiana Ernesto Breda|Breda]], [[Ikarus (Hungarian company)|Ikarus]], and [[Van Hool]].<ref name="braddock1995">Braddock, Andrew (March–April 1995). "Low-floor Trolleybuses – Making Access Easier". ''Trolleybus Magazine'' No. 200, pp. 30–37.</ref> The first [[Solaris Bus & Coach|Solaris]] "Trollino" made its debut in early 2001.<ref name="turzanksi2012">Turzanski, Bohdan (March–April 2012). "Trollino 500, Part 1". ''Trolleybus Magazine'' No. 302, pp. 28–35.</ref>{{rp|30}} In the former Soviet Union countries, Belarus' [[Belkommunmash]] built its first low-floor trolleybus (model AKSM-333) in 1999,<ref name="tm226-p89">''Trolleybus Magazine'' No. 226 (July–August 1999), p. 89.</ref> and other manufacturers in the former Soviet countries joined the trend in the early 2000s.

However, because the lifespan of a trolleybus is typically longer than that of a motorbus, the budget allocation and purchase typically factored in the longevity; the introduction of low-floor vehicles applied pressures on operators to retire high-floor trolleybuses that were only a few years old and replace them with low-floor trolleybuses.<ref name="tm222-p122">"Low-floor or Long Life?" (November–December 1998). ''Trolleybus Magazine'' No. 222, p. 122. National Trolleybus Association (UK).</ref> Responses varied, with some systems keeping their high-floor fleets, and others retiring them early but, in many instances, selling them second-hand for continued use in countries where there was a demand for low-cost second-hand trolleybuses, in particular in Romania and Bulgaria. The [[Trolleybuses in Lausanne|Lausanne system]] dealt with this dilemma in the 1990s by purchasing new low-floor passenger [[trailer (vehicle)|trailers]] to be towed by its high-floor trolleybuses,<ref name="tm222-p122"/> a choice later also made by [[Trolleybuses in Lucerne|Lucerne]].

[[File:Vancouver trolley bus - New Flyer E60LFR.jpg|thumb|The [[Trolleybuses in Vancouver|Vancouver trolleybus system]] completed the transition to an exclusively low-floor fleet in 2009.]]
Outside Europe, 14 vehicles built by, and for, the [[Trolleybuses in Shanghai|Shanghai trolleybus system]] in mid-1999 were the first reported low-floor trolleybuses in Southeast Asia.<ref name="tm230-p39">''Trolleybus Magazine'' No. 230 (March–April 2000), p. 39.</ref> [[Trolleybuses in Wellington|Wellington, New Zealand]], took delivery of its first low-floor trolleybus in March 2003,<ref name="tm249-p39">''Trolleybus Magazine'' No. 249 (May–June 2003), p. 39.</ref> and by the end of 2009 had renewed its entire fleet with such vehicles.<ref name="bramley-tm306">Bramley, Rod (November–December 2012). "New Zealand: A 'Roller Coaster' Ride, Part 4". ''Trolleybus Magazine'' No. 306, pp. 126–134.</ref> Unlike Europe, where low floor means "100%" low floor from front to back, most "low floor" buses on other continents are actually only low-entry or part-low floor.

In the Americas, the first low-floor trolleybus was a [[Busscar]] vehicle supplied to the [[Trolleybuses in São Paulo|São Paulo EMTU system]] in 2001.<ref name="box-tm292">Box, Roland (July–August 2010). "More about the 2000s". ''Trolleybus Magazine'' No. 292, pp. 78–82. National Trolleybus Association (UK). {{ISSN|0266-7452}}.</ref> In North America, wheelchair lifts were again chosen<ref name="tm222-p122"/> for disabled access in new trolleybuses delivered to [[Trolleybuses in San Francisco|San Francisco]] in 1992–94, to [[Trolleybuses in Dayton|Dayton]] in 1996–1999, and to Seattle in 2001–2002, but the first low-floor trolleybus was built in 2003, with the first of 28 Neoplan vehicles for the [[Trolleybuses in Greater Boston|Boston system]].<ref name="box-tm292"/> Subsequently, the [[Trolleybuses in Vancouver|Vancouver system]] and the [[Trolleybuses in Philadelphia|Philadelphia system]] have converted entirely to low-floor vehicles, and in 2013 the Seattle and Dayton systems both placed orders for their first low-floor trolleybuses. Outside São Paulo, almost all trolleybuses currently in service in Latin America are high-floor models built before 2000. However, in 2013, the first domestically manufactured low-floor trolleybuses were introduced in both Argentina and Mexico.<ref name="tm311"/>{{rp|134}}

With regard to non-passenger aspects of vehicle design, the transition from high-floor to low-floor has meant that some equipment previously placed under the floor has been moved to the roof.<ref name="getting on board"/> Some transit operators have needed to modify their maintenance facilities to accommodate this change, a one-time expense.

==Double-decker trolleybuses==
[[File:Tetley Bitter Advert on Bradford Trolleybus Cropped.jpg|thumb|A trolleybus in [[Bradford]] in 1970. The [[Trolleybuses in Bradford|Bradford Trolleybus system]] was the last one to operate in the United Kingdom; closing in 1972.]]

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 & Son|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).<ref name="Murray"/> British manufacturers of double-deck trolleybuses included [[Associated Equipment Company|AEC]], [[British United Traction|BUT]], [[Crossley Motors#Buses|Crossley]], [[Guy Motors|Guy]], [[Leyland Motors|Leyland]], [[Karrier#Trolleybuses|Karrier]], [[Sunbeam Commercial Vehicles|Sunbeam]] and others.<ref name="Murray"/>

In 2001, [[Citybus (Hong Kong)]] converted a [[Dennis Dragon]] (#701) into a [[Double-decker bus|double-decker]] trolleybus,<ref name="tm238hk">''Trolleybus Magazine'' No. 238 (July–August 2001), pp. 73 and 88.</ref> and it was tested on a 300-metre track in Wong Chuk Hang in that year.<ref name="tm238hk"/> Hong Kong decided not to build a trolleybus system, and the testing of this prototype did not lead to any further production of vehicles.

==Use and preservation==
[[File:Троллейбус Крым 2015 август - panoramio.jpg|thumb|right|Monument to [[Crimean Trolleybus]]]]
{{Main|Trolleybus usage by country}}
There are currently 300 cities or metropolitan areas where trolleybuses are operated,<ref name="janes2012"/> and more than 500 additional trolleybus systems have existed in the past.<ref name="Murray"/> 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 2012, the majority are located in Europe and Asia, including 85 in Russia and 43 in Ukraine.<ref name="janes2012"/> However, there are eight systems existing in North America and nine in South America.<ref name="janes2012"/>
<!-- Do not add details of specific cities here; use the article Trolleybus usage by country (newly split out in September 2012)-->

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.<ref name="Murray"/> 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]]<ref name="tm295">Isgar, Carl F. (January–February 2011). "Preservation Update".  ''Trolleybus Magazine'' No. 295, p. 11. National Trolleybus Association (UK). {{ISSN|0266-7452}}.</ref> – but operation of trolleybuses does not necessarily occur on a regular schedule of dates at these museums.

==Faic cuideachd==
{{div col|colwidth=23em}}
* [[Battery electric bus]]
* [[Bus rapid transit]]
* [[Dual-mode bus]]
* [[Electric bus]]
* [[Electric-vehicle battery]]
* [[Electromote]]
* [[Guided bus]]
* [[Gyrobus]]
* [[List of trolleybus manufacturers]]
* [[List of trolleybus systems]]
* [[Overhead line#Parallel overhead lines|Parallel overhead lines]]
* [[Traction substation]]
* [[Trolleytruck]]
{{div col end}}

==Notes==
{{reflist|colwidth=30em}}

==Further reading==
* Bruce, Ashley R. ''Lombard-Gerin and Inventing the Trolleybus''. (2017) Trolleybooks (UK). {{ISBN|978-0-904235-25-8}}
* Cheape, Charles W. ''Moving the masses: urban public transit in New York, Boston, and Philadelphia, 1880-1912'' (Harvard University Press, 1980)
* Dunbar, Charles S. (1967). ''Buses, Trolleys & Trams''. Paul Hamlyn Ltd. (UK) [republished 2004 with {{ISBN|0-7537-0970-8}} or 9780753709702]
* McKay, John P. ''Tramways and Trolleys: The Rise of Urban Mass Transport in Europe'' (1976)
* Murray, Alan (2000). ''World Trolleybus Encyclopaedia''. Trolleybooks (UK). {{ISBN|0-904235-18-1}}
* Porter, Harry; and Worris, Stanley F.X. (1979). ''Trolleybus Bulletin No. 109: Databook II''. North American Trackless Trolley Association (defunct)
* [[Mac Sebree|Sebree, Mac]]; and Ward, Paul (1973). ''Transit's Stepchild, The Trolley Coach'' (Interurbans Special 58). Los Angeles: [[Interurban Press|Interurbans]]. LCCN 73-84356
* Sebree, Mac; and Ward, Paul (1974). ''The Trolley Coach in North America'' (Interurbans Special 59). Los Angeles: Interurbans. LCCN 74-20367

===Periodicals===
* ''Trolleybus Magazine'' ({{ISSN|0266-7452}}). National Trolleybus Association (UK), bi-monthly
* ''Trackless'', Bradford Trolleybus Association, quarterly
* ''Trolleybus'', British Trolleybus Society (UK), monthly

==Ceanglaichean a-mach==
{{commons|Trolleybus}}
*(in German) [https://www.trolleymotion.eu TrolleyMotion{{snd}}an international action group to promote modern trolleybus systems, and database of systems in the world]
*[http://www.trolleybus.co.uk/ British Trolleybuses]
*[http://www.tramz.com Trolleybuses in Latin America]
*[http://www.trolleybuses.net/index.htm North American trolleybus pictures]
*[https://public-transport.net/index_trolley.htm Trolleybuses in Europe]
*[https://transphoto.org Urban Electric Transit - Database/Photo gallery]


[[Category:Buses by type]]
[[Category:Trolleybuses| ]]
[[Category:Trolleybus transport| ]]
[[Category:Electric buses]]
[[Category:Sustainable transport]]
[[Category:Articles containing video clips]]