There are 72 variations, not so sure about tracks.
At least that's what it seams from this pic:
This was posted yesterday here in other thread, and as you can see this is the game status and as we know the AI level is set individually for each track variation individually, so it's possible to know how manny variations are based in it...
Holy moly, that´s a lot to drive on On a sidenote, I love how it keeps track of "total distance driven". I don´t know why but I´m a sucker for little game statistics like that
What a pity, no night tracks, at least I don't see it.
Even the GT4 evening tracks, like Seattle or Twin Ring Motegi are modified so we can't enjoy our car lights, not to mention the ones with concealable headlamps, we never see them up