I have been spending a lot of time making some new road textures, such as lines, pavements, etc.
I want to make proper road intersection corners for roads without sidewalks.
I have managed to make a rather nice Sidewalk corner, which looks like this:



Now, I want to make a corner without a sidewalk for rural roads. I made this texture:


However, the transparent parts are apparently not actually transparent, and CAW seems to think it knows what should be put there instead...


Upon closer look, the curve can be seen, but it continues the pavement texture beyond it:


It seems like CAW is simply not supporting transparency on surface textures (that is: non Road Detail textures), however both the sidewalk and dirt corner textures of the base game have transparency. How are they made?

what file format have you used? Have you googled for sims3 transparency templates for caw? I know there are transparency templates out there. I have them on my main machine, but I don't start it up that often these days. I use my laptop for school work. I don't quite remember, but I have been struggling with the same issues for Angkor Wat. I didn't get what I wanted either, but didn't have the time to check it out.

What I ended up doing lots of the time though, is to just paste my texture onto an EA texture to make it work. I don't know what is wrong, but it seemed to work at some time.

The format is DDS (BC3; Linear DTX5).
I have not tried searching for transparency templates. However, I don't understand your search... CAW doesn't exist for Sims 4, much less files templates for it in Sims 4.
[EDIT] Search results gave me nothing useful, only a few posts about this same issue with no real answers and well as a post about making transparent terrain paints (I am trying to make transparent road surfaces, not terrain paints).

Yes. I have 2 games to think about. It's typical of me to muddle them together. I will have to check what I have when I get to the stationary I do caw on. I have tried making transparency templates myself too, but I have to check on my stationary. I'm very busy with school these days.