I didn't always feel this way, but I think the use of cellphones has created and environment where even slow moving drivers are unpredictable. I now walk to work and frequently see people on their phones while driving, if a line of ten cars are stopped at a light at least three people are on their phones. The result isn't an extreme increase in accidents but a constricting deficit of attention which incrementally lengthens every encounter on the road. More short stopping, more people missing green lights or just driving super conservatively and not merging holding up traffic.
Also I never use my phone while driving, but the fact that I can't even look at it when I know someone is trying to contact me is incredibly frustrating and impacts my enjoyment of driving.