I work in Japan in the Anime industry and those are typical of many smaller and older towns. Never seen a spline of anything like that. Have not looked into Japanese routes in Trainz, that sounds like a great project. Any chance it will touch the steam era? that is my own special interest. Of course most of the steam infrastructure and stock was destroyed in the war, or much of it. but pre war it was a flourishing system of great interest, much of it modeled on the UK style but with some distinctive touches and widely used by everyone of all classes.
good luck on it, i am working on some japanese houses both rural and town, for a MSTS/Open Rails project but i can convert them to Trainz if it helps ..just have hands full at the moment with another project, give me a PM if you want to talk about things.
Chris