The .7z package contains a layout for "LA Canyons" in which the road has added one transparent top-most layer that reacts to dynamic changes of "Sol" weather. That way all of the original features of the road are preserved since it`s not replacement of the "main_roads.kn5".
Edit 07.02.2020 - Install: unzip in game`s "MODS" subfolder and use JSGME to enable or disable this add-on. If you want to use this road for races or traffic, edit the respective "models_******.ini" to add
[MODEL_25] FILE=lac_wet.kn5 POSITION=0,0,0 ROTATION=0,0,0
NB: In case of problems connecting servers which return the checksum error make sure the track`s layout you are using is in it`s original state.
Of course the "extension" subfolder has a role to play in this and it has to be present in the respective layout for the wetFX to work in CSP and make the road change from wet to dry in sync with Sol. It doesn`t replace the default "extension" for the whole track but works along with it.