Trolleybus

"Trackless trolley" redirects here. For the non-electric buses that resemble historic streetcars, see Tourist trolley.
Busscar trolleybus in São Paulo, Brazil
Solaris trolleybus in Landskrona, Sweden
Trolleybus in Cambridge, Massachusetts.
Video of a trolleybus in Ghent, Belgium

A trolleybus (also known as trolley bus, trolley coach, trackless trolley, trackless tram [in early years][1] or trolley[2][3]) is an electric bus that draws power 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 path, needing only one wire and one pole (or pantograph). They are also distinct from other kinds of electric buses, which usually rely on batteries. Power is most commonly supplied as 600-volt direct current, but there have been, and are, exceptions.

Currently, around 300 trolleybus systems are in operation, in cities and towns in 43 countries.[4] Altogether, more than 800 trolleybus systems have existed, but not more than about 400 concurrently.[5]

History

The "Elektromote", the world's first trolleybus,[6] in Berlin, Germany, 1882

The trolleybus dates back to 29 April 1882, when Dr. Ernst Werner Siemens demonstrated his "Elektromote" in a Berlin suburb. This experiment continued until 13 June 1882, after which there were few developments in Europe, although separate experiments were conducted in the U.S. In 1899, another vehicle which could run either on or off rails was demonstrated in Berlin.[7] The next development was when Lombard Gerin operated an experimental line at the Paris Exhibition of 1900 after four years of trials, with a circular route around Lake Daumesnil that carried passengers. Routes followed in Eberswalde and Fontainebleau.[8] Max Schiemann on 10 July 1901 opened the world's fourth passenger-carrying trolleybus system, which 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 Cantono Frigerio system was demonstrated near Milan.

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

A double-deck trolleybus in Reading, England, 1966

Leeds and Bradford became the first cities to put trolleybuses into service in Great Britain on 20 June 1911.[7] Apparently, though it was opened on 20 June, the public was not admitted to the Bradford route until the 24th. 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.[9] 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).[10][11]

Smaller trackless trolley systems were built in the US early as well. The first non-experimental system was a seasonal municipal line installed near 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 streetcars. In the U.S.A., 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.[12] Trackless trolleys were the dominant form of new post-war electric traction, with extensive systems in among others, Los Angeles, Chicago, Rhode Island, and Atlanta; Boston, San Francisco (California), and Philadelphia (Pennsylvania) 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.[13]

A trolleybus in Qingdao, China

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 300 cities or metropolitan areas are served by trolleybuses today.[4] (Further detail under Use and preservation, below.)

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, Tallinn, Varna, Vilnius and Zurich, as well as smaller ones such as Arnhem, Bergen, Coimbra, Gdynia, Kaunas, Lausanne, Limoges, Luzern, Modena, Piatra Neamţ, Plzeň, Prešov, Salzburg, Solingen, Szeged, Târgu Jiu and Yalta. See also Trolleybus usage by country.

Transit authorities in some cities have reduced or discontinued their use of trolleybuses in recent years, while others, wanting to add or expand use of zero-emission vehicles in an urban environment, have opened new systems or are planning new systems. For example, Lecce, Italy, opened a new trolleybus system in 2012, and new systems are planned in Leeds and Montréal, among other places.

Vehicle design

Diagram of a 1947-built Pullman Standard model 800 trolleybus, a type still running in Valparaíso (Chile).
  1. Overhead line (overhead wires)
  2. Destination or route sign
  3. Rear view mirror
  4. Headlights
  5. Boarding (entry) doors
  6. Direction (turning) wheels
  7. Exit doors
  8. Traction wheels
  9. Decorative elements
  10. Retractors/retrievers
  11. Pole rope
  12. Contact shoes
  13. Trolley poles (power collector)
  14. Pole storage hooks
  15. Trolley pole base and fairing/shroud
  16. Bus Number

Advantages

A San Francisco Muni trolleybus (ETI 14TrSF) climbing Nob Hill
Irisbus Cristalis trolleybus in Limoges, France

Comparison to Trams

Comparison to Motorbuses

Trolleybuses 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, an electric storage system on the vehicle or the wire system, 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". Lastly, for routes that have more frequent stops, use of trolley bus eliminate the pollution brought forth during idling, thus also improved air quality
Indicator for a wire switch[14]
Pole bases with springs and pneumatic pole lowering cylinders
Insulated poles, contact shoes, and pull–ropes

Disadvantages

Comparison to Trams

Note: As there are numerous trams and light-rail technology, the disadvantages listed may be applicable only with specific technology or design.

Comparison to motorbuses

Off-wire power developments

On this articulated 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 Public Service Company of New Jersey, with 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 Muni in San Francisco, 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. 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 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 diesel-electric power units for operating short distances off-wire were placed in service by SEPTA in 2008 are, instead of using a conventional diesel drive train or battery-only system for their off-wire movement.[18]

A dual-mode bus operating as a trolleybus in the Downtown Seattle Transit Tunnel, in 1990

King County Metro in Seattle, Washington and the 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. The MBTA uses dual-mode buses on its new (2004-opened) Silver Line (Waterfront).

Other considerations

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.

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 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.

Wire switches

Trolleybus wire switch

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 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.[19] (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[19] 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[20] 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

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.[5]:114 In the 2000s it was effectively rendered obsolete by low-floor designs.

Well over 200 different trolleybus makers have existed – mostly commercial manufacturers, but in some cases (particularly in China), built by the publicly owned operating companies or authorities.[5]:91–125 Of the defunct or former trolleybus manufacturers, the largest producers – ones whose production totalled more than 1,000 units each – included the U.S. companies Brill (approx. 3,250 total), Pullman-Standard (2,007), and Marmon-Herrington (1,624); the English companies AEC (approx. 1,750), British United Traction (BUT) (1,573), Leyland (1,420) and Sunbeam (1,379); France's Vétra (more than 1,750); and the Italian builders Alfa Romeo (2,044) and Fiat (approx. 1,700).[5] Also, Canadian Car and Foundry built 1,114 trolleybuses based on designs by Brill.[5]

As of the 2010s, at least 30 trolleybus manufacturers exist. They include companies that have been building trolleybuses for several decades, such as Škoda since 1936, Trolza (formerly Uritsky, or ZiU) since 1951 and New Flyer, among others, along with several younger companies. Current trolleybus manufacturers in western and central Europe include Solaris, Van Hool and 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/FSU countries. 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, which had built more than 860 trolleybuses since 1979, was acquired in 1998 by Volvo. However, Dina, which is now that country's largest bus and truck manufacturer, began building trolleybuses in 2013.[21]:134

Transition to low-floor designs

Starting in the early 1990s using systems introduced low-floor bus models, which began only a few years after the first such models were introduced for motorbuses. These have gradually replaced high-floor designs, and by 2012, every existing trolleybus system in Western Europe had purchased low-floor trolleybuses, with the La Spezia (Italy) system being the last one to do so,[22] and several systems in other parts of the world have purchased low-floor vehicles.

In the United States, the Americans with Disabilities Act of 1990 required that all new transit vehicles placed into service after 1 July 1993 be accessible to persons in wheelchairs.[23] Some transit agencies had already begun to accommodate such passengers by purchasing buses with wheelchair lifts, and early examples of fleets of lift-equipped trolleybuses included 109 AM General trolleybuses built for the Seattle trolleybus system in 1979 and the retrofitting of lifts in 1983 to 64 Flyer E800s in the Dayton system's fleet.[24]:61

One of the NAW/Hess articulated trolleybuses delivered to Geneva in 1992, which were among the first production-series low-floor trolleybuses

Trolleybuses in other countries continued to lack disabled access until the 1990s, when the first two low-floor trolleybus models were introduced, both built in 1991, a "Swisstrolley" demonstrator built by Switzerland's NAW/Hess and an N6020 demonstrator built by Neoplan.[25][26] The first production-series low-floor trolleybuses were built in 1992: 13 by NAW for the Geneva system and 10 Gräf & Stift for the Innsbruck system. By 1995, such vehicles were also being made by several other European manufacturers, including Skoda, Breda, Ikarus and Van Hool.[27] The first Solaris "Trollino" made its debut in early 2001.[28]:30 In the former Soviet Union countries, Belarus' Belkommunmash built its first low-floor trolleybus (model AKSM-333) in 1999,[29] and other manufacturers in the former Soviet countries joined the trend in the early 2000s.

However, due to the lifespan of a trolleybus typically is 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.[30] Responses varied, with some systems keeping their high-floor fleets, and others retiring them early but, in many instances, selling them secondhand for continued use in countries where there was a demand for low-cost secondhand trolleybuses, in particular in Romania and Bulgaria. The Lausanne system dealt with this dilemma in the 1990s by purchasing new low-floor passenger trailers to be towed by its high-floor trolleybuses,[30] a choice later also made by Lucerne.

The Vancouver trolleybus system completed the transition to an exclusively low-floor fleet in 2009.

Outside Europe, 14 vehicles built by, and for, the Shanghai trolleybus system in mid-1999 were the first reported low-floor trolleybuses in Southeast Asia.[31] Wellington, New Zealand, took delivery of its first low-floor trolleybus in March 2003,[32] and by the end of 2009 had renewed its entire fleet with such vehicles.[33] 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 São Paulo EMTU system in 2001.[34] In North America, wheelchair lifts were again chosen[30] for disabled access in new trolleybuses delivered to San Francisco in 1992–94, to 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 Boston system.[34] Subsequently, the Vancouver system and the 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.[21]: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.[23] Some transit operators have needed to modify their maintenance facilities to accommodate this change, a one-time expense.

Double-decker trolleybuses

A trolleybus in Bradford in 1970. The 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 (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).[5] British manufacturers of double-deck trolleybuses included AEC, BUT, Crossley, Guy, Leyland, Karrier, Sunbeam and others.[5]

In 2001, Citybus (Hong Kong) converted a Dennis Dragon (#701) into a double-decker trolleybus,[35] and it was tested on a 300-metre track in Wong Chuk Hang in that year.[35] 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

There are currently 300 cities or metropolitan areas where trolleybuses are operated,[4] and more than 500 additional trolleybus systems have existed in the past.[5] 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.[4] However, there are eight systems existing in North America, nine in South America and one in Oceania, specifically in New Zealand.[4]

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.[5] 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[36] – but operation of trolleybuses does not necessarily occur on a regular schedule of dates at these museums.

See also

Notes

  1. ↑ 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.
  2. ↑ Dunbar, Charles S. (1967). Buses, Trolleys & Trams. Paul Hamlyn Ltd. (UK). Republished 2004 with ISBN 0-7537-0970-8 or 9780753709702.
  3. ↑ "Trolley service begins the next 60 years" (Press release). TransLink. August 16, 2008. Archived from the original on 19 July 2011. Retrieved 6 September 2012.
  4. 1 2 3 4 5 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.
  5. 1 2 3 4 5 6 7 8 9 Murray, Alan (2000). World Trolleybus Encyclopaedia. Yateley, Hampshire, UK: Trolleybooks. ISBN 0-904235-18-1.
  6. ↑ Elektromote, Siemens History website on 14 August 2015
  7. 1 2 Charles S. Dunbar, Buses, Trolleys and Trams (Paul Hamlyn Ltd, 1967, no ISBN), p. 81 et seq.
  8. ↑ Henry Martin, Lignes Aeriennes et Trolleys pour Automobile sur Route (Libraire Polytechnique Ch., 1902, no ISBN), p. 29 et seq.
  9. ↑ Dunbar p. 84
  10. ↑ Dunbar p. 83
  11. ↑ J. S. King, Keighley Corporation Transport, (Advertiser Press Ltd, 1964, no ISBN) p. 39 et seq.
  12. ↑ Dunbar, p. 90 of
  13. ↑ "Plan for city trolleybus comeback". BBC News. 15 June 2007. Retrieved 2009-06-03.
  14. ↑ G. Cebrat. "Greenfleet". Greenfleet.info. Retrieved 2010-11-29.
  15. ↑ "Power in downtown Vancouver won't be fully restored until Tuesday". CBC News. 14 July 2008. Other reports stated that the (electrical) explosion did not affect power supply to the trolleybuses (only implied by this article).
  16. ↑ Ashley Bruce. "Overhead". Tbus.org.uk. Retrieved 2010-11-29.
  17. ↑ "Electric Trolley Bus Fact Sheet" (PDF). Seattle Department of Transportation. Retrieved 2012-03-29.
  18. ↑ Trolleybus Magazine No. 267 (May–June 2006), p. 71. National Trolleybus Assn. (UK).
  19. 1 2 Electric Vehicle Technologies at the Wayback Machine (archived March 3, 2006). Transport 2000 BC. Archived from the original on 2006-03-03.
  20. ↑ 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.
  21. 1 2 Trolleybus Magazine No. 311 (September–October 2013).
  22. ↑ Trolleybus Magazine No. 305 (September–October 2012), p. 119.
  23. 1 2 "Getting on board" (July–August 1993). Trolleybus Magazine No. 190, pp. 86–87. National Trolleybus Association (UK).
  24. ↑ DeArmond, R. C. (May–June 1985). "The Trolleybus System of Dayton, part 2". Trolleybus Magazine No. 141, pp. 49–64.
  25. ↑ Trolleybus Magazine No. 179 (September–October 1991), pp. 100–101.
  26. ↑ "The Neoplan N6020 Low-Floor Trolleybus". Trolleybus Magazine No. 183 (May–June 1992), p. 68.
  27. ↑ Braddock, Andrew (March–April 1995). "Low-floor Trolleybuses – Making Access Easier". Trolleybus Magazine No. 200, pp. 30–37.
  28. ↑ Turzanski, Bohdan (March–April 2012). "Trollino 500, Part 1". Trolleybus Magazine No. 302, pp. 28–35.
  29. ↑ Trolleybus Magazine No. 226 (July–August 1999), p. 89.
  30. 1 2 3 "Low-floor or Long Life?" (November–December 1998). Trolleybus Magazine No. 222, p. 122. National Trolleybus Association (UK).
  31. ↑ Trolleybus Magazine No. 230 (March–April 2000), p. 39.
  32. ↑ Trolleybus Magazine No. 249 (May–June 2003), p. 39.
  33. ↑ Bramley, Rod (November–December 2012). "New Zealand: A 'Roller Coaster' Ride, Part 4". Trolleybus Magazine No. 306, pp. 126–134.
  34. 1 2 Box, Roland (July–August 2010). "More about the 2000s". Trolleybus Magazine No. 292, pp. 78–82. National Trolleybus Association (UK). ISSN 0266-7452.
  35. 1 2 Trolleybus Magazine No. 238 (July–August 2001), pp. 73 and 88.
  36. ↑ Isgar, Carl F. (January–February 2011). "Preservation Update". Trolleybus Magazine No. 295, p. 11. National Trolleybus Association (UK). ISSN 0266-7452.

Further reading

Periodicals

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