Guessing from your picture your terrain is a .dae object and you use Over Object for your decalroad. As far as I remember this function is sometimes buggy because the nodes may not correctly snap to the mesh, it will sink into or float above the mesh if you move it. You can check the nodes and replace some of them to see if it works, or split the road into segments and try. Another possibility is that it's just not refreshing with your changes, and you can refresh the road by editing some properties of the decalroad and then change that back, e.g. hide and unhide, change road texture. Sorry for my English, hope I've described that correctly!
Your image is broken for me, but I can venture a guess: while it's technically possible to place a decalroad on a static mesh or groundplane, I've found that this only works if the level also has a terrain block too for some reason.
