Articulated bus
An articulated bus (either a bendy bus, motor bus or trolleybus), is a bus which is articulated, essentially meaning it can bend in the middle. They are usually of single-deck design. They comprise two rigid parts linked together by a pivoting joint. This arrangement allows a longer legal overall length, and thus a higher passenger capacity than rigid single decker buses, while still allowing the bus to be turned within the limitations of the roads it is used on.
Articulated buses have various synonyms known around the world alluding to their articulated nature, such as tandem buses, bendy buses, banana buses, slinky buses, caterpillar buses or accordion buses. Due to their high passenger capacity, articulated buses are often used as part of bus rapid transit schemes, and can include mechanical guidance.
Used almost exclusively on public transport bus services, articulated buses are approximately 18 metres (60 ft) in length, compared to standard rigid buses which are usually 11 to 14 metres (36 to 46 ft) long. The common arrangement of an articulated bus is to have a forward vehicle with two axles towing a rear trailer portion which has one axle, although the driving axle can be either on the front or rear vehicle. 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 crab-like fashion, similar to hook-and-ladder fire trucks operating in city environments.[1] A less common variant of the articulated bus is the bi-articulated bus, where the vehicle has two trailer portions instead of one. Their capacity is around 200 persons, and their length about 25 metres (82 ft).
Contents |
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 Australia and Europe (Austria (Gräf & Stift)[1], Italy, Germany (Gaubschat, Emmelmann, Göppel, Duewag, Vetter), Hungary (Ikarus), etc.) The first modern bendy buses in the UK were built by Leyland-DAB and used in the city of Sheffield, United Kingdom in the 1980s, but were withdrawn from service as they proved expensive to maintain.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 larger doors, much larger passenger capacity (120+ versus 80−90), increased stability from a lower center of gravity, a sometimes smaller turning radius, higher maximum speed, and accessibility to people with disabilities and the elderly.
One disadvantage that appears in some articulated bus is the effective motive power available to it. It is common for articulated buses to use the same engine as non-articulated buses (for example the Hungarian Ikarus 260 solo and IK 280 bendy share a common 10,350 cubic centimetres (631.6 cu in), 192 brake horsepower (143 kW; 195 PS) inline six diesel engine). 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 case if the bus is powered by a diesel engine. 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.[2] However, no overheating or fire incidents have ever been recorded in Vancouver's articulated electric trolley buses due to this. Likewise, articulated trolley buses were specifically chosen due to the higher torque output of electric motors, which typically outperform diesel-based low floor buses.
Under certain urban circumstances (such as in areas with high pedestrian volumes and narrow streets and tighter turns), articulated buses may also be involved in significantly more accidents. Estimates for the London articulated buses put their involvement at pedestrian accidents at over five times as high as for all other buses, and over twice as high with cyclist accidents. During a period in which articulated buses made up approximately 5% of the London bus fleet, they were involved in 20% of all bus-related deaths, statistics which eventually led to their replacement.[3] Some element of these safety statistics may however be skewed by the buses being used on the busiest routes (in the most crowded areas of town), thus making them look worse than the buses they were being compared with.[4]
Use
Articulated buses have been used in most European countries for many years. Until 1980, they were illegal on roads in the UK. Experiments by South Yorkshire Passenger Transport Executive, 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.[5]
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. Boris Johnson, the current Mayor of London has promised to rid the city of the controversial buses, and all articulated buses on route 38 already been decommissioned. He aims to replace all remaining buses within 12 years with a new generation of open-platform Future Routemaster.
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 600 kilowatts (816 PS; 805 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 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 centers such as Baltimore, Boston, Minneapolis-St.Paul, Chicago, Denver, Houston, Columbus, San Diego, Los Angeles, New York City, Pittsburgh, Orange County, California, Philadelphia, Phoenix, the Quad Cities, San Francisco, Seattle, and Washington, DC. In Canada they are used in Vancouver, Ottawa, Calgary, Edmonton, Halifax, suburban Montreal, London, southern York Region Hamilton, 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, Shanghai, and Hangzhou. 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.
In Singapore, articulated buses were first introduced in 1996 by Trans-Island Bus Services (now SMRT Buses) with the Mercedes-Benz O405G buses (bodied by Hispano). They were given the moniker "bendy buses", a name which is still in use today. In April that same year, SBS Transit introduced a demonstrator Volvo B10MA bus (registration SBS998Y), fitted with a three-door version of the Duple Metsec bodywork, similar to the Volvo B10M buses done by the said company. This bus, at 19 metres (62 ft), earned the title of "Asia's Longest Bus". In 1997, SBS Transit purchased another bendy bus, the Mercedes-Benz O405GN (registration SBS999U), again as a demonstrator. This bus had Volgren CR221 bodywork (as compared to the Hispano-and-later-Pininfarina-bodied buses of SMRT Buses), never before seen in Singapore. In March 2006, SBS Transit sold all of its bendy buses to New Zealand, after having encountered driveability problems with the Volvo B10MA bus and air-conditioning issues on the Mercedes-Benz bus, and also deciding that double-decker buses were able to carry more passengers while taking up less road space at the same time, as compared to "SMRT's stand that articulated buses offer greater accessibility and efficiency".[6]
Types of buses
Articulated buses can be of "pusher" or "puller" configuration.[1] In pusher buses, only the rear C-axle is powered by a rear-mounted internal combustion 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 considered an outdated design by some, as it prohibits floor levels lower than approximately 750 millimetres (30 in), and can causes passenger 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. This type of bus also performs better in snow or ice conditions as the thrust from the drive wheel dose not cause the vehicle to jacknife. Also unpowered C-axle is much simpler and freed form engine weight, easing installation of counter-steering to further decrease turning radius.
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.
Although the majority of bendy buses utilise diesel engines for their motive power, a number of operators (primarily outside of North America and by LACMTA) are adopting compressed natural gas (CNG) 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 AG Buses 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 specialise 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 metres (82 ft) 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 Bus GmbH built a handful of Neoplan Jumbocruisers between 1975 and 1992. In these models, it is possible to move between the two parts via only the upper deck, so they have separate doors and two sets of stairs.
See also
- Trailer bus
- Articulated buses in the United Kingdom
References
- ↑ 1.0 1.1 "Articulated Transit Bus Steering Considerations". North American Bus Industries. http://www.nabiusa.com/resource_page.cfm?res_id=11#. Retrieved 2007-01-07.
- ↑ "Bendy-buses withdrawn after fires". BBC. BBC News. 24 March 2004. http://news.bbc.co.uk/1/hi/england/london/3563279.stm. Retrieved 2007-01-07.
- ↑ Johnson ditches London's bendy buses
- ↑ Bendy buses - the fatal facts
- ↑ The Bendy Bus: A Transport Revolution Ingenia Magazine, March 2005
- ↑ http://sbs3758d.fotopic.net/c1644378.html. Desmond Tay. 27th January 2009. Retrieved 2009-11-13.
External links
|
||||||||||||||
|
||||||||||||||