here is what i found on cynamite
http://www.cynamite.de/Gran-Turismo...iels-von-der-gamescom-Praesentation-768487/3/
and a fast translation with google "yeah sry about that" Oo
"The next feature of the track editor of Gran Turismo 5 was unveiled that is truly unique in this form. Falls from the junk box is not really complicated, but works independently totally random routes. As a player, it only determines the environment, the weather, the density curve or how tight should be the curves. In every curve can be tailored for each sector. There is also the choice of circuit or rally circuit. Self-created routes may be followed, of course, stored and shared with friends."
so in my view it is not a real "editor" more a random track with some weather etc. to choice!