1st Which version of OMSI 1 or OMSI 2 is being used? Omsi2 - Editor
I always though that it was not possible, in the game, to create those kind of patern, where you connect 3 splines together to make and onramp or offramp with splines :
But after playing and looking at Express91.06c, I figured that this trick was used using the default invisstreet splines from the base game.
I'm pretty sure that you need to use an object to do this but it looks like there is any in this case.