East Yorkshire Motor Services and Reading Buses have both converted early model Alexander Dennis Enviro400H hybrids to straight diesel mechanical drive, retaining their fourcylinder Cummins ISB engines.
Both operators’ vehicles were early production models purchased with Department for Transport Green Bus Fund assistance, Reading Buses receiving 31 in 2010/11 and East Yorkshire taking 10 in 2011 for operation in Hull.
East Yorkshire is in the process of converting all 10, undertaking the conversion work at its Scarborough depot with assistance from a third party engineer. Four of them are already back in service equipped with a conventional gearbox and water-cooling system in place of their original BAE Systems HybriDrive.
‘They were delivering the fuel savings but had become unreliable and expensive to maintain and the imminent battery replacements were going to be very costly,’ says company chairman Peter Shipp. ‘The modified buses are very reliable so far.’
The prospect of replacing expensive batteries — Oxford Bus Company cites a figure of £35,000 per bus — is also driving Reading Buses’ search for an alternative driveline for its Enviro400Hs. It has had one converted to a plug-in electric with a small gas engine acting as a range extender and has now modified another in similar fashion to the East Yorkshire conversions.
Chief executive officer Martijn Gilbert says: ‘It retains the four-cylinder engine and I’m pleased to report that it is performing extremely well so far.’ The Reading vehicles are longer wheelbase versions.
Unlike Volvo, Wrightbus and Optare, which fit four-cylinder Euro6 engines in their B5TL, StreetDeck and MetroDecker double-deckers, and Alexander Dennis uses the 4.5litre fourcylinder Cummins in the much improved current versions of the Enviro400H, the only production option on the straight diesel Enviro400 is the 6.7litre six-cylinder ISB.