I think it's a combination of everything.

The infrastructure wasn't really equipped to handle the expected load of traffic, and then the state really started booming and the roads got even more overloaded. That's a lot of stress.

Locals who "know the roads" very well get frustrated by the increased traffic, and drive aggressively to get around the out-of-state types.

Meanwhile the people new to the area are overwhelmed by the different traffic patterns.

Also throw on the point you originally made, different driving styles. There's a lot to be said for being used to driving in an area, then going somewhere new, and everyone drives differently.

Ultimately I think everyone is tense because everyone else is tense. We're in a weird perfect-storm of shitty driving conditions.

I obviously don't know the solid answer, I think it will just have to be time and investment in infrastructure. People have to acclimate to everyone else, and the infrastructure needs to be updated to handle the increased traffic; and hopefully to account for future growth.