This kind of question crops up frequently and comes from thinking of Trainz in model railway/railroad terms whereas it is in fact a railway/railroad simulator. One can imagine a route as being to any scale one likes - even five barleycorns to the ell, to go back a few (hundred) years in the UK - but it makes no difference whatever to the size of the models. The best approach in my view is to enjoy Trainz for what it is and take full advantage of the enormous space offered compared with even the largest model railway/railroad.
If thinking in a non-standard modelling scale is really important, the answer would be to make a measuring spline in GMax or Blender. I've just made - because I needed them - two splines (visible only in Surveyor) which place a marker every five or ten metres, to help with accurate spacing of assets like street or platform lamps, tram poles, etc. I will upload these to the DLS when I've taken screenshots.
Speaking of screenshots (and way off topic, I know) I've also made what I call a Photostage for taking screenshots of individual models without needing to create a background or seeing grid lines etc. It's a simple platform 100 metres square, with a background dividing it into two halves, one plain for buildings etc., the other with a length of updating track for rolling stock.
Ray