Well, the fact that people stayed and survived to procreate[1] suggests that it's not all doom, or at least not for the relevant prior occasions (This Time May VaryTM).
Anyway, what you need to have is some situation where not being in the city is easier and more convenient than staying. This involves getting out. (If you're pretty sure the roads are going to be clogged up, perhaps you'd rather prefer to risk it in your town-house... But if you're a resident of a 'mobile' home park, on the outskirts, with your truck already gassed up and no elderly or infirm members of the family you need to manhandle (probably protesting) onto the garden chair in the flatbed, and there's nothing on telly[2], then you take a jaunt, way ahead of most of the urbanites that have just decided to flee from the inner environs.
Really, I'm stuck for something (not already mentioned) that'll get anywhere near a total evacuation. Now, if Friendly Aliens (or Pretending-To-Be-Friendly-Aliens, who were the actual cause of the hypothetical disaster) were to offer to pluck every individual up with their combined Tractor Beams/Transporter Devices/Sky Hooks/whatever, and what's more offer to transport everyone to a replacement city, built so that everyone gets a fully equipped replica of their original home and an extra 50% floorspace/other improvement, and with the added benefit of magnificent views of whichever moons of Saturn are not the ones they are actually on, with all the appropriate environmental measures (and one or other easy transportation option available to visit their non-City families and friends almost as if nothing had happened), then maybe there'd be an uptake.
But, really, if something happened like that erroneous assumption that Cern would suck us all into a black hole of our own making, I'm betting there'd be plenty of people waiting around for a good view from the 'rim' of the expanding crater caused by the singularity's consumption of the Earth. (I mean, you could go to the other side of the world, still ultimately get consumed and yet have had a rubbish view, all things considered. Personally I could see myself setting up a chair and seeing what I could see, before that pesky Event Horizon obscured most of my view, or that pesky Spaghettification tore me apart, whichever came sooner.) Albeit that this seems like an overkill disaster, given the OP's original presumptions. (A provably 'localised' black-hole-consumption-effect might pursuade me to move to just beyond where the military set up their checkpoints to keep over-inquisitive people from outside out, and Invisible Warp Demons From Another Dimension in.)
(Ninjaed a bit, so put the quote at the top to qualify what I'm actually replying to.)
[1] Or at least survived to see their offspring, who also stayed and also procreated, unless we're talking about Pappy and Grandpappy not evacuating at the point last year when Junior (themselves beyond middle age) brought them over to the island for the first time.
[2] Apart from The Disaster. Actually, that's probably the clincher. "Hey, there I am! There I am! See that insignificant white spot in the middle of that trailer park, just slightly in front of the wave of destruction! Let me open a window! Hey, Maw! Look! I'm on teevee!"
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Topic: Making a City Evacuate (Read 7041 times)