People are people, the world over, without even an attempt at enforcing the traffic speed limit laws, people, even those who know better will and do take advantage. Try driving the speed limit on 95 or the Rickenbacker and watch the angry reaction from your fellow drivers, if you doubt it. It is not that they don't know what the speed limit is, it is that they know that they will not be ticketed for speeding.
Driving in Miami is frustrating, our lights seem timed against the flow of traffic, without any coordination between them. Sometimes I think it would be better if every single light in Dade County turned at the exact same moment, at least then the light 1 block away, wouldn't turn red as soon as the one you are sitting at turns green.