Volvo B9S

The Volvo B9S was an articulated bus chassis constructed by Volvo Buses between 2002 and 2011. It was available as a low-entry bus (the B9SALE), a wholly low-floor bus (the B9SALF), and an integral bus bodied by Volvo (the 7500 or 8500).
The B9S was successful in few countries. It has been commercialized in Sweden, where it has been in use in the urban systems of Stockholm, Östergötland, Umeå and Gothenburg, being used there as a rapid transit buses; in Chile where it was a part of the biggest purchase order for Volvo buses: 1,159 articulated units entrusted for the urban system of Santiago; and in Brazil to be used in urban system of Sao Paulo by rapid transit corridors, in articulated and bi-articulated versions. Production of the B9S ceased in Europe in 2011 due to poor profitability, with Volvo offering the existing Volvo B9LA as a successor, which is rear-engined and used the same engine as in final generation of B9S.
History and Evolution of the Platform.
The B9S was launched in 2002 to replace the Volvo B7L, although production of the latter continued nonetheless. It was intended to replicate the success of the Volvo B10MA and Volvo B12MA in the past. So in this way, the new chassis was conceived initially as a mid-engined articulated bus, with low floor at least in 40 percent of his length and using an engine of less than 10 liters of displacement, taking advantage of the fact that Volvo had launched at that time a new 9,4 liter engine used in the FM truck series, appearing as alternative against models such as the Van-Hool AG300 and AGG300 that were using 12 liter engines. Placing a vertical engine in the centre of the front-most section of the articulated bus allows to avoid a wider useless space and to free up space in the back and create an even weight distribution throughout the bus favoring better on-road capabilities. Unlike the B10MA/B12MA that came before it, however, the B9S has a step-free entrance and is fully accessible to wheelchairs. 
Initially made on the plant of Volvo Buses in Borås, Sweden, it was offering in two versions: as Low Entry named B9SLEA, and as entirely Low Floor called B9SALF, offering in a front-most section wheelbase of 6.4 meters and bodied by Säffle, as a complete Volvo 7500 bus. The units made up to 2005 used the Volvo D9A engine with 340 bhp, later to that year they used the Volvo D9B engine with 360 bhp in order to achieve the Euro 4 and Euro 5 emissions rules. In year 2005 the production of this platform was extended to Volvo Buses' factory in Curitiba, Brazil, with external bodyworks to answer to the order of purchase of 1,159 B9SALF articulated units to be part of the urban system of Santiago of Chile, which involved to a modification of the front-most section to 5 meters, in order to avoid problems of maneuverability in narrow streets. From this year this platform is offered for the South American market, being entrusted later near 100 additional articulated units for Chile and 100 bi-articulated units for Brazil, between the year 2007 and 2010.