[1rudeboy]

One of which lives in the country, and is adapted to carnivores, and another group that lives in the city, and is adapted to cars?

I don't think it's unreasonable to assume that squirrels "adapt" to being around cars. A good number of dogs and cats do.

One thing I think you fail to recognize (sticking up for rural squirrels, here) is their perspective. Meaning that they observe the approaching car from six inches above the ground. Maybe they simply can't process the visual cue quickly enough . . . which might explain the erratic/panicked/whatever behavior.

I don't know, I've never laid my head on the pavement to watch an approaching car. I do know that, when driving, tapping the horn appears to help them make up their minds.

[Daffynition]

Here's what you 'n grey whiskers fail to realize ... the squirrel is showing YOU a behavior ... and YOU are the one who is supposed to imitate their zig-zag behavior with your car. See? It's simple. Nutty but simple. ;)