The speed limit is 55, of course, but that only bothers people who believe the cops will slow down that much to pull them over. So, the freeways are fast. 4 lanes each direction seems to be the norm, with the big freeways being 6 or even 8 lanes in each direction. All travelling 80 mph. The drivers, having their agressions stimulated by the driving speed, are just obnoxious.
Nobody uses turn signals, they are a sign of weakness.
Nobody slows down to merge or change lanes, you speed up to do that. If you need to go somewhere, you floor the accelerator, and take your space. It only works because everyone is expecting you to act like that, too. If you signalled and waited for a space to open up, you would never change lanes. I'm not normally an agressive driver.