Tram-train's are operating in quite few EU countries already.
And by co-incidence the first Tram-train set for testing purposes in the UK arrived only a few days ago.
There are to be tests on the Sheffield network with an extension over the Network Rail lines from Meadowhall into Rotherham in around a years time.
The main concerns of the rail industry are potential crash resistance and tyre wear as rails have differing profiles.
On satisfactory completion of tests the Manchester system may move forward to converting a number of suburban routes from heavy rail to Tram-train.
All irrelevant to Glasgow through.