Cities have dabbled with temporary bans on cars before, but rarely (if ever) on this scale. Paris just held a third "Day Without Cars" that forbade nearly all private transport across the complete core of the city -- about 40 square miles of it. If you visited between 11AM and 6PM local time on October 1st, you had to bike, walk or take public transit like buses and taxis to make your way around the City of Lights. And officials were strict about enforcing the car ban, too. You risked facing a fine between €90 and €135 ($105 to $159) if you drove without an emergency or another good reason (such as visiting an elderly relative), and you still had to honor a 30KM/H (about 19MPH) speed limit on top of that.