I beg to differ. Exodus of ~1m people in about one day is frequently observed in Europe. It can't be done with cars, of course, because cars are not a means of mass transportation. It can be done easily with trains, though.

Example: Street Parade Zurich, attended by about a million people. Virtually all of those people arrive by train immediately before the event, and are gone the next day. Watching > 100k people pour out of a train station in less than an hour is really a spectacle. Remember that Zurich is not a huge city in the first place.

Example: Paris goes on holiday. All-but-literally everybody leaves Paris for summer holiday, pretty much simultaneously. You don't know what an urban evacuation means until you've witnessed this.