I'm not much of a pixelartist, but I've extended all roadtypes in pak64 to include diagonals as well. One zip file contains the paks, which will when extracted in the right place overwrite the old roads. The other zip file contains the changed image and dat files, so you can change things around if you don't like them.
You can find the files here:
http://www.combuijs.nl/ftp/pak64_diagonal_roads_pak.zip (http://www.combuijs.nl/ftp/pak64_diagonal_roads_pak.zip)
http://www.combuijs.nl/ftp/pak64_diagonal_roads_source.zip (http://www.combuijs.nl/ftp/pak64_diagonal_roads_source.zip)
Nice effort; but still vehicles keep driving outside the road. This was, which tose are not included in the standard pak so far. Timothy find a nice way out of this. I just lacked the time to do them like this.