Ah, I wish. Unfortunately, Greeks (not just Athenians) suffer from a horrible case of car-i-itis, meaning they have to go everywhere by car (I swear, people get in their car to go get milk or cigarettes) and every family must own a couple of cars, etc. This makes it a lot harder to pedestrianise large parts of the city, if nothing else because there's no space to put all those cars, other than on "pedestrianised" streets.
I've seen this often. Once, I was sitting at a cafe in a "pedestrianised" street and first one, then a second car, came through, in touching range of where I was seated - in a narrow street half of which was already occupied (illegally) by the cafe's chairs and tables. That has stuck into my mind because I have a big mouth and there was an er altercation with the drivers and some of his friends who was actually sitting at the same cafe as me and my friends. Anyway it's a common occurrence and a hard problem to solve.
Don't even think about going around on a bicylce in Athens, of course. You'll just cut years off your life, either because you'll be breathing cars' exhausts constantly or because someone will just run you over.