i think that the way gets blocked by some cars is not a bug, but perfectly fine. I would expect some troubles if you flee from a giant. And if you have to wait for him until he crushes that cars flat and... try to avoid getting underfoot is kind of funny. So i think there is no fix needed.... and how should you fix that? the cars fly randomly.^^
The giantess mode has indeed some bugs. I think there are too many objects in one direction... so the grafix card has extreme amount of work when you look into that direction.