I always loved Steve Jackson's Car Wars ...
"Drive offensively. The life you save may be your own."
Seriously now, I've driven all over the US.
I'd say New England -- especially Connecticut -- are the absolute worst. Why? Because you will have people doing 90mph on the Interstate and then people doing 20mph! Speed doesn't kill, but difference in speed does kill! It's the place you will consistently see people moving at 40-50mph DIFFERENCE from each other in the same direction. DEADLY!
At least in Atlanta, everyone does the same speed for the most part -- about 20mph over the limit. When someone doesn't, that's a problem, but not as bad as doing 20mph under the limit like in New England.
New York drivers are the most efficient. Although I've never driven outside the US, I do know that American drivers are too hesistant, and don't know how to merge efficiently. We've been spoiled with superhighways and other things. But in New York, they're much more like non-US drivers -- they know how to move efficiently, because it's the only way to get somewhere.
You'll never see more stalled cars than in Las Vegas. People out of money, with not enough for gas.
BTW, the worst place to obey the speed limit is on I-95 south through the space coast. Always do 5mph over the limit! If you drop to just under the speed limit heading south, they will pull you over and assume you are running money to buy drugs and "trying not to be conspicuous." By strictly obeying the law, they think you are very conspicuous! Just FYI, in case you travel on I-95 in Florida -- at least in east central Florida.
I keep up to speed with traffic, typically 5mph over. I use the on-ramp/off-ramp to accelerate/decelerate -- not before and not after. If people did that, we'd decrease the number of accidents ten-fold! Why?
Remember, difference is speed kills (and not speed itself).
At 15mph difference, you double the chances for an accident.
At 20mph difference, you triple the chances for an accident.
It's exponential from there -- which is why 15mph is usually used to increase fines/points, and you can be arrested at 25mph over in some locales.
Which is why I would like to see an uniform speed limit zone law here in the US.
10mph neighborhood, be prepared to stop.
25mph residential or downtown, you may need to stop at times (no minimum).
40mph for intra-city highway, 25mph minimum, no excuses (except turn lanes)
55mph for inter-city highway, 40mph minimum, no excuses, period
70mph for interstate or major highway, 55mph minimum, strictly enforced
left lane "maximum safe speed" for western US states with 25+ miles between exists, right lane is 70/55 max/min (as previous), left lane is minimum 70mph and "maximum safe speed."
In this uniform speed limit zone design, other than 25mph, no speed differential should be more than 15mph!