Hi all,
I have a simple setup, a directional light and some planes on the ground, I have built some roads meshes and puting them over ground makes this kind of glitch in the shadow, I check if there is any not-attached edge or the images have any alpha area on the edges or something but all seem to be correct, just the shadow seem to detect where the road wall is and make that kind of light line there where it ends, Im using Unity 5.6.1. Thanks beforehand for any help =)

I believe this is called “Shadow Acne” which is a problem in unity, and possibly not your fault, it basically happens when a mesh does not have inside depth (2d) and the light of the directional light leaks through the mesh. Just turn down Shadow Bias and i believe that should be fixed.