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 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 buses without steps and having low floors along their entire length, 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. Some consider this an outdated design, as it prohibits floor levels lower than approximately 750 millimetres (30 in), and can produce passenger discomfort due to high noise and vibration levels. On the other hand, the puller bus is cheaper to manufacture, and can be used in very narrow or severely potholed streets. This type of bus also performs better in snowy or icy conditions, as the thrust from the driving wheels does not cause the vehicle to jacknife. Also, the unpowered C-axle is much simpler and carries no engine weight, facilitating the installation of counter-steering mechanisms to further decrease the turning radius.
Modern low-floor pusher articulated buses also tend to suffer from suspension problems because their wheels lack the ampleness of travel that would enable them to absorb surface unevennesses. This also leads to passenger discomfort and relatively rapid disintegration of the vehicle's superstructure.
Although the majority of articulated 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 in order 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 Hungarian-made Ikarus 280, the articulated version of the Ikarus 260, of which more than 200,000 buses were 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 in which both the B-axle and C-axle were driven, with a driveshaft passing through the turntable between the two driving axles. Very few companies specialise in manufacturing the articulated section for the buses. One that does is ATG Autotechnik GmbH in Siek near Hamburg.
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