I wish I could help. It never has happened to me that way. What I´ve experienced, is the game freezing when pausing and selecting restart in a long track, or one that requires most of the PS3 power, like the full Nurburgring, or Nurburgring time change, time change La Sarthe, etc. But this happens when I´ve just started the game, like if it hasn´t load everything yet, or something.
Possible solutions:
Install the full game. I haven´t tried that yet, but it might work.
Sign off the PSN if not playing online. Other than the game freezing like three times since I got it, I have never had any other problems regarding lagging, disappearing roads or such... Most people that have problems are the ones with old beat up PS3´s working all the time, as well as being online all the time. I know that most of you guys are all about playing online, but there is proof that when signing off, the game stops showing these problems, in like 80% of the cases. The good care of your console always helps. Again, I know that most of you treat the PS3 like a computer, but I can assure you that thats killing your PS3. I have a five year old 40GB PS3, and it has never shownd any signs of malfunctioning. I keep it free from dust, well ventilated, and I don´t have it on for more than two to three hours a day, when temperatures are "friendly"( it can get up to 86 degrees farenhiet in these summer days). Sometimes I don´t even use my PS3 for days if I´m more into my old PS2 games.
