On Fri, 23 Dec 2005 00:26:51 +0000, "Alan J. Flavell"
wrote:

To the best of my recollection, some German trolleybuses have (or have
had) a fully fledged diesel motor, used routinely on the outer parts
of their routes, and only switch to/from OHL power for the more
central parts of the town/city. Evidently, in the event of a problem
(road blockage, OHL or power failure) they would be capable of
continuing in service on the other power source.

Seattle's system does this, running as trolley buses underground
through the city centre, and using diesel once on the surface. They
are articulated but I don't know who made them.
--
Terry Harper
Website Coordinator, The Omnibus Society
http://www.omnibussoc.org