Articulated bus
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Articulated buses, also known as bendy buses, accordion buses or jointed buses, have an increased passenger capacity. Found almost exclusively in public transportation use, these buses are usually around 60 feet (18 meters) long, while a regular bus is 35 to 45 feet (11 to 14 meters). To make them nimble enough to safely navigate streets at their increased length, they are fitted with an extra pair of wheels and a joint (usually located slightly behind the midpoint of the bus, behind the second pair of wheels). 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 firetrucks operating in city environs.
Some buses have two joints, and these are called bi-articulated. These are exotic and usually run in separate and often auto-guided lanes (quasi-trams or bus rapid transit). Some rare combinations between double-decker and jointed buses also exist, but neither are in common use.
Advantages and disadvantages
The main benefits of an articulated bus over the double-decker bus are increased stability (lower centre of gravity), lower roadwheel pressure, higher maximum speed, and compatibility with handicapped or elderly people. Bendy 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, Germany and Croydon (London Borough), United Kingdom, where double-deckers and trams coexist in some areas. Bendy buses are more suitable for mass transit purposes, because they have more doors (usually three dual-lane and one single-lane door or four duals) for rapid exchange of passengers.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 buses; this leads to a slower speed and acceleration, due to an increase of weight. When used in cities with many slopes (such as Vancouver, B.C.), the vehicle may overheat, leading to stalling in the milder case and a fully fledged fire in the worst case.
Use
Articulated buses have been used in most European countries for many years, however, they were considered illegal on British roads until 1980. Experiments by South Yorkshire PTE with buses by MAN and Leyland-DAB during 1979 led to the change, but the experiment was abandoned in 1981. Double-decker buses were generally considered less expensive to purchase and operate. The cost of the strengthened deck framing and staircase was more than offset by the additional axle(s) and coupling mechanism of an articulated bus. The additional weight of these components also led to higher operational costs. 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. Notably in London, they, with their double-decker counterparts, have replaced AEC Routemasters on all routes. Elsewhere in the UK they are generally operated on specific routes to bolster patronage rather than on entire networks.
In Israel, articulated buses — commonly called long buses — are very common, 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.
A bendy bus is a long vehicle and usually requires a specially trained driver, as maneuvering can be difficult (particularly reversing). 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 bendy can be subject to unusual centripetal forces, which can be a discomfort for many people although it's not an issue in Pushers (See Below). Nonetheless the bendy 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 "Volan" companies also run hundreds of articulated buses on intercity lines. Surprisingly, some people still regard any bendy as exotic, especially in Asia and the USA where any public transport except for single section buses are almost unknown. Major exceptions are Philadelphia, New York City, San Francisco, Boston (on the Silver Line BRT system and the #39 rail bustitution line), Seattle, and Chicago.
Types of buses
Bendy 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 bendy buses the diesel 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 bendy bus is cheaper to make and can be used in very narrow or severely pot-holed streets. Also, modern, low-floor pusher articulated buses usually suffer from suspension problems, because their wheels cannot have enough travel to absorb street unevenness, leading to passenger discomfort and relatively rapid disintegration of the superstructure (unless the road network is overhauled and constantly maintained to near-racetrack standards). 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.
Although the majority of bendy buses are diesel powered, a number of operators are adopting compressed natural gas power to reduce pollution. In North America, many transit authorities are adopting bendy buses that are diesel-electric hybrid powered, such as the New Flyer DE60LF or the North American Bus Industries 60-BRT Hybrid.
A typical puller bendy is the articulated version of the Ikarus 280 from Hungary, with more than 200,000 buses manufactured between 1973-2000, mostly for Soviet bloc customers. Well-known makers of pusher-type articulated buses include Mercedes Benz, Renault Agora, Volvo in Poland, etc.
The Belgian manufacturer Van Hool offers a bi-articulated bus of 25 m length with a capacity of about 180 passengers. In September 2002, fifteen were deployed on line 12 in the Dutch city of Utrecht, connecting the downtown railway station to office, college and university buildings at the edge of the city.[#endnote_UtrechtLine12] More have been added since. These buses are also used in the German cities of Hamburg (Metrobus 5) and Aachen (lines 5 and 45), where single articulated buses alone were not able to handle the huge amount of passengers per day.
Volvo have made a few bi-articulated buses running in Gothenburg. They are based on their pusher articulated low-floor bus model with the engine mounted on the floor on the side of the bus, and the cooling system on the roof.
The Brazillian bus body manufacturer Induscar CAIO has made many bi-articulated buses on top of Volvo chassis. They are currently used in São Paulo (without air conditioning) and Curitiba (with air conditioning). Those buses, called 'Top Bus' by Induscar, were nicknamed 'metrô sobre pneus' ('metro over tires') in Curitiba, and 'Martão' (something like 'Big Marta') in São Paulo, as a reference to the mayor Marta Suplicy, whose public transport program, Interligado, included those buses.
Reference
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External link
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