Thanks all!
@Ulco: I have a method to even out the road angle against the hill angle somewhat (but not completely). To be clear I'm talking about the effect that the road would tilt in one direction if it runs alongside a hill. But this method is pretty destructive if the angle gets too high, and it has other unwanted side effects. So all in all, no, I don't have a really good solution yet.
And indeed, the dashed line would have to be created using a trigenometric function. Something based on e^sin(x) s going to be best I reckon, rounded up with a hard step or so.
Regards,
Frank