1) Add the road texture to the terrain
2) Create a road with EasyRoads3D Free tool. (read EasyRoads3D documentation)
3) Before clicking "Finalize Object" do the following:
- Check Apply Splatmap checkbox in the Road Object (Terrain Settings section)
- Choose your road texture
- Setup other parameters in the Terrain Settings section.
4) Click Finalize Object
5) Delete The road object from the scene.