invisible one way road (to control town expansion)

[robo]

you can use this invisible one way road to surround towns as a barriere and towns won't expand over it. There are other possibilities, for example you can create protected space in towns to plant trees or other things.
Junctions are not possible and computer opponents don't use this invisible road.
You can see these invisible one way roads only if you activate the build menu for roads. They can be build and removed the same way as normal one way roads and have to be activated in the sceanario editor if you want to use them (I called it "protected space"). They use only the brick bridge.
First I tried to show trees instead of invisble roads, but they looked too steril.
I made a quick game and didn't encounter any problems, but I'm not experienced with these things, so suggestions for improvments are always welcome.