That's the problem. If it is the day when in group think, everyone decides to leave, you will be in a traffic jam that can take hours to get to the airport. With 5 million cars on the road on exodus day, assuming 2 passengers per car (probably a very low estimate), ten million, or more than one out of six people living in Italy will be on the highway that day. It is the mother of all traffic jams when you get stuck in that. That's why I'd pay attention, and consider a late train or cab to the Airport Hilton if it looks like I'm going to get stuck in that.