I've sometimes wondered why modern tramcar makers don't make double deckers.
Suggestions:
(1) Do you need two bods to 'police' both decks when one will do for an artic.

(2) With tightly knotted streets and high peak demand such as you would get in
say for example Dundee when the mill shifts ended, the smaller footprint would
be desirable. These conditions have largely gone.

(3) If you want a tunnel for your trams to burrow through the city centre or
just do dive-unders you're adding to the civil engineering costs.

--
Peter 'Prof' Fox
Multitude of things for beer, cycling and curiosities at www.vulpeculox.net
2 Tees Close, Witham, Essex, England +44 (01376) 517206