It's the perfect storm:
1. Aging and outdated infrastructure not meant to handle the amount of vehicles (of all types) on the roads. All the while PennDot is building a 6 lane highway west of Harrisburg to the middle of nowhere.
2. Aging population - PA is the 2nd "oldest" state in the country with the 2nd highest percentage of elderly, just behind Florida, leading to more of the "me first" and "I don't care about anyone behind me, I'm going to cruise in the passing lane b/c I'm going 2 miles over the speed limit" attitudes on the road.
3. Many folks from NY/NJ who have moved into the state over the last decade for cheaper housing adding both extra cars on the roads and those cars are usually filled with aggressive drivers.