Thank you all for your suggestions.

I'm not inclined to change the 'rules' at this time.

The so called rules are just guidelines and we all go Off Topic and off
on Tangents from time to time (including me).

The aim of the guidelines is to have a focussed group.  That focus is
trams (and light rail) meaning railed public transport in an urban
setting, often in the streets.

Inclusion of heavy electric rail and trolleybuses reflect the edges of
that focus.

No bus, including a trolley bus, has the key characteristics of light rail.

There are many other groups, including on facebook which allow
discussion of heavy rail and bus topics in full.

Mal Rowe -  dictator, but hopefully a benevolent example of the genre