I do not see any good reason for any of the parameters to be other than normal metric units, so that a unit of bulk cargo should be one ton. Passengers are a bit different, it looks like a unit of passengers is four persons. I guess that is in order to keep a reasonable number of people walking around.
It seems the power curve used for steam engines is wrong, initial acceleration is quite fast. A steam locomotive has good pulling power from a standstill, but poor acceleration. Rated effect is only available at maximum speed. This is why they are not fond of grades – they cannot shift gears.
For road vehicles it looks like the rolling resistance of carriage wheels on dirt roads is seriously underestimated, and even on cobblestones carriages move rather too easy.
Keeping at least the internal workings working rationally with SI units will avoid lots of misunderstandings and bugs. If users want to see something different, it can always be converted for display.