I have to believe it's the perils of living in, or close to, a large city. Some days I would prefer a small town.
In the Minneapolis area "minnesota nice" doesn't always apply. I get to work @ 6, I leave early (around 3 pm) and am lucky. Why? Because after 3:30, the rush hour starts and lasts until 6 pm at least.
Lots of road construction around here makes detours, which overloads other roads, and people just are in a real big hurry. On Highway 100 which is what I mainly drive, it's routine to have people doing 70-80 mph - speed limit is 60 and I drive around 60-65. Each week it seems I have someone cut me off, tons of people tailgating me, flashing their lights - even in the right lane.
It's not as bad as OP described their city. At least we don't seem have a lot of accidents.
In general, I believe it's a loss of respect for each other. We all want to get home quick so we can pursue that happiness.