It only happens when there is alot of Post Processing going on, especially when there are more than one veichele crashing on screen, during the race at once.
Since each physic engine of the cars crash is offloaded to the SPE's.
I can understand the code not being fully optimized? Perhaps, but who em I to say something like this? Its a first gen game, for what it does, and what it is; its one of the best!
Imagine the possiblities of MS 2?