I may well be wrong on this, but purely from a laymans point of view it
seems to me that Boris's new buses tend to glide around quietly with the
diesel engine off for quite a lot of the time. The older style buses that
also are marked as "hybrid" however seem to have their diesels turning over
constantly and barely less engine noise than an ordinary bus.

Is there some significant difference in the way they work or are the older
style ones just ****?

--
Spud