Articulated bus

Articulated buses (either motorbuses or trolleybuses), also known as tandem buses, bendy buses, banana buses, slinky buses or accordion buses (and not to be confused with Flxible buses), are buses of a type with an increased passenger capacity. Found almost exclusively in public transportation use, these buses are approximately 18 m (60 ft) long, while regular buses are 11 to 14 m (35-45 ft) long. To make them nimble enough to safely navigate streets at their increased length, they are fitted with an extra axle (set of wheels) and a joint usually located slightly behind the midpoint of the bus, behind the second axle. Some models of articulated buses have a steering arrangement on the rearmost axle which turns slightly in opposition to the front steering axle, which allows the vehicle to negotiate turns in a somewhat crab-like fashion, an arrangement similar to that used on long hook-and-ladder fire trucks operating in city environments.cite web
url = http://www.nabiusa.com/resource_page.cfm?res_id=11#
title = Articulated Transit Bus Steering Considerations
publisher = North American Bus Industries
author =
date =
accessdate = 2007-01-07 ]

Some buses have two joints, and these are called bi-articulated buses. Their capacity is around 200 and their length about 25 m (82 ft). These are rare and usually run in separate and often auto-guided lanes (quasi-trams or bus rapid transit).

History

Early examples of the articulated bus appeared in Europe in the 1920s. In the mid-1960s, AC Transit in California pioneered the use of a modern articulated bus, operating the experimental General Motors bus "XMC 77" on one of its transbay lines. Articulated buses have also been used in Vienna, Austria, since 1963, where Gräf & Stift automakers pioneered their use. [http://www.wienerlinien.at/wl/ep/programView.do?contentTypeId=1001&channelId=-17080&displayPage=%2Fep%2Fprogram%2FcontentOverview.jsp&programId=10723&pageTypeId=9322] The first modern bendy buses in the UK were built by Leyland and used in the city of Sheffield, United Kingdom in the 1980s, but were withdrawn from service as they proved expensive to maintain.

Advantages and disadvantages

The main benefits of an articulated bus over the double-decker bus are rapid simultaneous boarding and disembarkation through more and large doors, much larger passenger capacity (120+ versus 80-90), increased stability from a lower centre of gravity, higher maximum speed, and accessibility to people with disabilities and the elderly. Articulated buses can be used in some cities with a tram network, while double-deckers sometimes cannot fit under the overhead electric cable; however, there are other cities, such as Berlin, Croydon in London, and Singapore, where double-deckers and trams coexist in some areas, and Hong Kong, where the trams are also double deckers.

One disadvantage that appears in an articulated bus is the effective power available to it. It is common for articulated buses to use the same engine as non-articulated busesFact|date=March 2008; this leads to a slower speed and acceleration, due to an increase of weight. When used in cities with many slopes (e.g. Vancouver, B.C. or San Francisco, California) the vehicle is prone to overheating, leading to stalling in the milder case and a fully fledged fire in the worst caseFact|date=March 2008.

Use

Articulated buses have been used in most European countries for many years. Until 1980, they were considered illegal on roads in the UK. Experiments by South Yorkshire PTE with buses by MAN and Leyland-DAB during 1979 led to a change in the law, but the experiment was abandoned in 1981 because Double-decker buses were generally considered less expensive to purchase and operate. The cost and weight of the strengthened deck framing and staircase in a Double-decker was lower than the cost and weight of the additional axle(s) and coupling mechanism of an articulated bus. Modern technology has reduced the weight issues, and the benefits of a continuous low floor allowing easier access and additional entrance doors for smoother loading have seen a reconsideration of the use of articulated buses.

Articulated buses became popular in mainland Europe as a means of increasing capacity. In many cities lower railway bridge clearances have precluded the use of double deck vehicles and they have never gained great popularity there. Overhead wires for trams, trolleybuses etc. are not really relevant as the minimum normal clearance above road level is standard across the EU and is well clear of a double deck vehicle (otherwise many goods vehicles would have severe problems).

In London, articulated buses and their double-decker counterparts, have replaced AEC Routemasters on most routes. Elsewhere in the UK they are generally operated on specific routes to bolster patronage rather than on entire networks.The recent popularity of articulated buses in the UK is because any double deck vehicle must be full seated upstairs. This limits the capacity to around 80 - 90 depending on the seating layout downstairs. An articulated single deck vehicle can be mainly of 'standee' configuration with a much lower percentage of people seated than a double deck vehicle. This however gives it a much higher capacity (120 - 140) for an 18 metre vehicle. With the same one driver, this should notionally reduce the cost per passenger kilometre, although their multi door design does present very real challenges in ensuring that all revenue is actually collected due to passengers in London entering through all three doors. The vehicles are also more expensive to buy and maintain and use more fuel than conventional double deck buses so it may be some time before the true economics of their operation can be assessed.

In Israel, the use of articulated buses—commonly called "long buses"—is widespread, particularly in Gush Dan and Jerusalem, the two great urban centers of the country. The long buses are considered reliable and useful and they served in Israel since the mid-seventies. During the Israeli-Palestinian conflict, such buses were often targeted by Palestinian terrorists and suicide bombers during rush hours, since a crowded long bus can contain more than 100 passengers. Due to the al-Aqsa Intifada wave of mass bombings, security measures were enforced and today many long buses in Israel are accompanied by a security guard.

An articulated bus is a long vehicle and usually requires a specially trained driver, as maneuvering (particularly reversing) can be difficult. Articulated electric trolleybuses can be difficult to control with engines having momentary peak power in excess of 500 kW (800 hp). The trailer section of a "puller" bus can be subject to unusual centripetal forces, which can be a discomfort for many people although this is not an issue in "pushers." Nonetheless the articulated bus is a total success in Budapest, Hungary, where the BKV city transit company has been running more than one thousand of them every single day since the early 1970s. The Hungarian company Volán also runs hundreds of articulated buses on intercity lines.

Articulated buses are common fare in the US urban centres such as Boston, Minneapolis-St.Paul, Chicago, Columbus, Detroit, MI, Los Angeles, New York City, Orange County, California, Philadelphia, the Quad Cities, San Francisco, Seattle, and Washington, DC. In Canada they are used in Vancouver, Ottawa, Calgary, Edmonton, Halifax, suburban Montreal, London, and Mississauga. In Asia, many major Chinese cities had fleets of articulated buses prior to the late 1990s. Many of these fleets have since been replaced by single section units, with the exception of a few cities, namely Beijing. In South America in São Paulo, Curitiba, Santiago and Bogotá.

In Adelaide, Australia, articulated buses are used on the O-Bahn guided busway. The first Articulated buses to use it were the Mercedes Benz O305G buses, however three MAN SG280H buses are also fitted for O-Bahn use. Trouble has been encountered in recent years trying to find suitable low-floor articulated buses as replacements for the 1984-built Mercedes buses. Unfortunately the design of the O-Bahn track prohibits most modern type of articulated bus.

Types of buses

Articulated buses can be of pusher or puller configuration. In pusher buses only the rear C-axle is powered by a rear-mounted engine and the longitudinal stability of the vehicle is maintained by active hydraulics mounted under the turntable. This modern system makes it possible to build entire length low-floor buses without any steps, which simplifies access for passengers with limited mobility. In puller articulated buses, the engine is mounted under the floor between the front and middle A- and B-axles, and only the B-axle is powered. This is an outdated design, which prohibits floor levels lower than approximately 750 mm (30 in) and causes passengers discomfort due to high noise and vibration levels. On the other hand, the puller bus is cheaper to make and can be used in very narrow or severely pot-holed streets Fact|date=June 2008. Also, modern, low-floor pusher articulated buses usually suffer from suspension problems, because their wheels lack ample travel to absorb street unevenness, leading to passenger discomfort and relatively rapid disintegration of the superstructure Fact|date=June 2008. During late 2003, early 2004, a series of onboard fires on newly delivered Mercedes-Benz Citaros led to Londoners humorously nicknaming the vehicles "chariots of fire". Mercedes-Benz quickly addressed the problem, although the vehicles were out of service for a period.cite web
url = http://news.bbc.co.uk/1/hi/england/london/3563279.stm
title = Bendy-buses withdrawn after fires
publisher = BBC News
author =
date = 24 March, 2004
accessdate = 2007-01-07 ]

Although the majority of bendy buses are diesel powered, a number of operators (primarily outside of North America and by LACMTA) are adopting compressed natural gas power to reduce pollution. Many other transit authorities in the United States and Canada are adopting articulated buses that are diesel-electric hybrids such as the New Flyer DE60LF.

A typical puller model is the Ikarus 280, the articulated version of the Ikarus 260, from Hungary, with more than 200,000 buses manufactured between 1973 and 2000, mostly for Soviet bloc customers. Well-known makers of pusher-type articulated buses include Mercedes-Benz, New Flyer Industries, and Scania. In the past, Volvo and MAN produced puller bendies but both manufacturers have since abandoned these designs for more modern pusher designs. The Renault PR 180 and PR 180.2 (articulated versions of the PR 100 and PR 100.2) were a special variation of the pusher design where both the B-axle and C-axle were driven, with a driveshaft passing through the turntable between the two driving axles. There are very few companies that specialize in manufacturing the articulated section for the buses. One company that does is ATG Autotechnik GmbH in Siek near Hamburg.

Bi-articulated buses

Articulated buses have been extended further since the late 1980s, with the addition of a second trailer section, extending the bus to near tram length and capacity as a Bi-articulated bus. The Chinese manufacturer Zhejiang Youngman (Jinhua Neoplan) has developed the 25-meter JNP6280G bi-articulated bus, deemed the "world's largest", which will be used in Beijing. Bi-articulated buses are still rare, having been trialled and rejected in some places. Due to their length, they find use on very high capacity routes, or as part of a bus rapid transit scheme.

Double-decker articulated buses

A few attempts have been made to create a double-decker articulated bus. Neoplan built a handful of Jumbocruisers between 1975 and 1992. In these models, it is only possible to move between the two parts via the upper deck, so they have separate doors and two sets of stairs.

See also

* Trailer bus
* Articulated buses in the United Kingdom

References

External links

* [http://www.nabiusa.com/resource_page.cfm?res_id=11 Steering Considerations & Engine Placements]