I will try to explain it more detailed using the example of curbstones.
VERTICAL is not usabel in this case, because when the road is steep, the curbstones will be distortet (comparison1.jpg).
So the best option would be ADAPTATIVE, but in this case the curbstones will not stay straight and get twistet alont the path (comparison2.jpg).
Is there a way to lock the rotation along the path?