I don't think it would be bad to increase the length on those very long trams.
I think, with the updated length calculation code, the sheffield supertram (34.5m) doesn't fit inside 1 tile anyways, on some rotations.
And then there is also the Edinburgh Tram, which is slated to be 42.85m long, which definitely doesn't fit inside one tile.
I already mentioned that the Edinburgh Tram would be more than one tile. Sheffield Supertram can also be more than one tile as there should be a Manchester Metrolink (29m) available at a similar time which does fit in one tile.
In summary trams which should fit in one tile (at most) are:
DLR stock (all varients 8+8)
Croydon CR4000 (8+8)
Manchester T-68 (8+8)
Manchester M5000 (8+8)
Birmingham T-69 (length 7+7)
Tyne and Wear Metro (length 7+7)
Units of each type should be able to be coupled together to form longer trains.
Ones which should be scale length are:
Croydon Variobahn (prototype is 18=4+4+2+4+4, 4+4+2+4 could be allowed fitting into one tile?)
Edinburgh Tram (prototype is 24=4+4+2+4+2+4+4, 4+2+4+2+4 could be allowed fitting into one tile, maybe allow 4+4+2+4+2+4+2+4+4=30?)
Birmingham Urbos 3 (prototype is 19=4+4+3+4+4, 4+4+3+4 could be allowed fitting into one tile?)
Sheffield Supertram (prototype is 20=8+4+8 - no alternatives)
I've given prototype lengths for these with suggested alternatives that we could let players choose to enable them to fit in one tile. Should players be given this choice or is that just a needless complication?
Some of these trams haven't been drawn yet it should be noted. Also for the Tyne and Wear Metro I can't get a source for a unit length, however from http://en.wikipedia.org/wiki/File:Tyne_and_Wear_Metro_Capacity_and_Saloon.jpg
it appears to be around 24m long (assuming a width of 2.6m), so easily fitting within one tile.