On Tue, 20 Dec 2011 13:00:28 -0000, "Graham Harrison"
wrote:

A double deck tram has by nature about
the capacity of a double deck bus, so given the choice the operator
opts for the bus which is more flexible and cheaper.

You're limiting your thinking. In effect I'm asking why you can't take a
modern multi section single deck tram and build a double deck version.

One reason might be that doubling the height does not enable a
doubling of the number of doors while lengthening a tram should allow
that. A single deck tram can also pass under lower off-road
obstructions where the OHLE does not have to allow for the passage of
the highest standard road vehicles.