Double-decker comeback

FRANK BEETON reports on important bus news from overseas.

Late in 2009 we reported on the competition staged the previous year by London’s mayor, Boris Johnson, for the design of a new double-decker bus for the British capital.

The objective was to find a layout that would replicate the success of the iconic AEC Routemaster, which served London with distinction from 1959 to 2005 and to take over from several generations of more recent double-deck and articulated single-deck replacements that were less than popular with the travelling public.

One of the two-person-operated Routemaster’s prime features was its open rear platform, which allowed passengers to hop on or off easily and quickly, but this could not be replicated in more modern single-operator designs. The design brief for the 2008 competition had included requirements for an open rear entrance, along with disabled access and green technology.

The joint winners of the £25 000 first prize in the 2008 competition were sports car manufacturer Aston Martin (working with architects Foster and Partners) and bus, coach and truck designers, Capoco Design. Both winning proposals were subsequently passed on to bus manufacturers, which were invited to tender their final detailed designs for consideration by the British capital’s public transport service authority, Transport for London.

Northern Ireland-based Wrightbus was declared the successful tenderer on 23 December 2009 and the company set to work on interpreting and developing elements of the competition-winning designs into a practical application. Its final design surprisingly featured no less than  three entrances, including the required open rear loading platform, and was unveiled in May 2010.

The Wrightbus design, developed in conjunction with Heatherwick Studio, is certainly striking and includes a number of interesting features. Dimensions are 11,2 m x 2,55 m x 4,4 m, with a seating capacity of 62 and provision for 25 standing passengers, plus one wheelchair bay. The entrances are positioned at the extreme front (opposite the driver), immediately behind the set-back front axle and at the rear nearside corner. These are complemented by two staircases leading to the upper deck – one opposite the central entrance and the other in the traditional rear offside corner position. Both staircases are well illuminated by adjacent transparent panels which have been cleverly integrated into the styling of the vehicle. The rear platform can be closed at off-peak times, allowing the bus to be operated by one person when passenger loads are reduced.

The published technical specification of the bus includes a diesel-electric hybrid drive system made up of a high-performance, low-emission diesel engine driving a generator to sustain a lithium-phosphate battery pack. This, in turn, provides power to electric drive motors.

Regenerative braking is also employed to return recovered kinetic energy to the battery pack. In the absence of any published detailed layout, it can be assumed that the hybrid system is of the “series” type, with no mechanical connection between the engine and the drive axle, and it appears most likely that mobility is enabled by individual rear wheel motors, rather than through a live rear portal-type axle with shaft drive from one electric motor.

The presence of cooling vents, at the offside rear and between decks above the rear loading platform, suggest that these are the most likely locations for the diesel engine and battery pack, respectively.

It has been reported that development of the new design will cost £7-million, but the unit cost is expected to work out at around £300 000 when orders are finally placed for several hundred buses.

This project has its critics, who have branded it “an exercise in vanity” by Boris Johnson. But the mayor certainly appears to be fully committed to the project and a running engineering prototype is currently under test, with the first trial unit expected to be delivered before the end of this year. Production units are planned to follow during the course of 2012.