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 so long that they would not otherwise be able to negotiate city traffic. 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). 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 a double decker (e.g., the London Routemaster 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.
On the negative side, articulated buses have been criticised as being dangerous to cyclists and motorcyclists, as the driver cannot fully control the path of the vehicle as it goes round corners.
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.
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.
Articulated buses in use
- Arnhem: operates bendy trolleybuses.
- Bangalore: bendy buses are operated by BMTC(Corporation).
- Boston: Siemens-built dual-power rubber-tire diesel/electric hybrid articulated buses were recently rolled out on the MBTA's South Boston Piers Transitway subway line.
- Chicago: very old fleet of articulated buses were to be phased out in 2002, but the CTA changed its mind and purchased a new fleet of articulated buses instead. Used on only a few heavily congested routes.
- Dublin
- Geneva: operates bendy trolleybuses to and from the airport.
- Groningen (city): operated by Arriva and NoordNed.
- Hamburg: uses single articulated buses, currently testing double articulated buses (as of 2004).
- Miskolc: runs 133 bendy buses on 33 of the 45 bus lines of the city.
- Munich
- New York: Used on many Bronx and Manhattan Routes.
- London: Bendy buses are used on routes 507, 521, 436, 453, 18, 149, 25 and 73. They were introduced and then withdrawn after several caught fire, then reintroduced after safety checks were completed.
- Ottawa: operated by OC Transpo.
- San Francisco: Muni currently has 60 articulated buses in use.
- Singapore: Bendy buses are operated mainly by SMRT Corporation.
- Utrecht (city) - bi-articulated buses.
- Vancouver, British Columbia: Operated by Translink on some high-capacity 'B-Line' routes.
- Washington DC: WMATA operates a large fleet of artic's on its urban and suburban routes.
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