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 longer than a standard bus. Lengths of these buses usually are around 60 feet, while a regular bus is 35 to 45 feet. To make them nimble enough they are fitted with an extra pair of wheels and a flexible 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 fire trucks operating in city environs.

Some buses have two flexible 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.

The main benefits of a bendy 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 would not fit under the overhead electric cable; however, there are other cities, such as Berlin, where double-deckers and trams coexist in some areas. Bendy buses are more suitable for mass transit purposes, because they have more doors (usually 3 dual-lane and 1 single-lane door or 4 duals) for rapid exchange of passengers.

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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-deck 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 are being used to replace AEC Routemasters on certain routes.

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 target by Palestinian terrorists and suicide bomber during rush hours, since crowded long bus can contain more than 100 passangers. 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.

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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 bendy can be subject to unusual centripetal forces, which can be a discomfort for many people. 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 the USA and Asia.

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 is a modern system, which makes it possible to build entire length low-floor buses, which do not have any steps and you can get in from the pavement. 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 app. 750 mm (30") and hurts passengers with high noise and vibration levels. In contrast, the puller bendy bus is cheaper to make and can be used in very narrow or severely pot-holed streets.

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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.

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). Engine nacelle fire in pusher bendys is also a common peril, probably because the hot-running, turbo-assisted, rear-mounted engine is fitted into a very cramped space with non-optimal cooling layout. Fortunately, city buses are fitted with diesel fueled engines, which means fires seldom cause personal injury, yet serious damage to the vehicle is quite common. 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.

Contents

Articulated buses in use

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Cities which no longer have Articulated buses

See also

External links

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