Splinebased grass tool erasing

hey guys, maybe one of you can help me out a little bit here.

i am trying to figure out how to get spline informations of an terrain into my procedurally material.

as you can see the RED square shows the painted landscape with gravel under the road , while the White one is just grass painted …

the material is a mix of landscape layer blend and automatic lerping from grass to rocks based on vertex gradient

my question how is :" how can i achieve getting the spline info and erase the grass beneath it WITHOUT layer painting it so i can simply drag splinestreets into the world and it refreshes its foliage "

i want to get rid of the layer painting thing, thank you very much for help , if theres no solution i have to paint every road by myself Q.Q :smiley: