I hope its strictly an American fantasy to think you're driving out of anywhere when something like that happens.

Buy a bicycle.

Following Hurricane Sandy, many were left without power and ultimately even gas was strictly rationed. So it's not out of the ordinary to imagine an event like that happening.

https://www.nj.com/news/2012/11/sandy_gas_ration_12_counties...

In Phoenix we all live in the shadow of the Palo Verde nuclear generation plant. And once on the radio I heard some pundits discussing contingencies if PV should glitch out and have a life-threatening disaster. And they matter-of-factly said, "you're gonna be walking." And that would be the truth; in a full-scale evacuation of a city like Phoenix, the freeways are not built to accommodate traffic like that, and yours truly has no car anyway, so I would be packing light and walking in the opposite direction, and/or ignoring the orders, to meet whatever fate awaits.

But I bet there would be a lot of bicycle and vehicle theft going on, in such an event.

I know I have a problem with "suspension of disbelief" but I find it always weird in those dystopian movies where they all drive monster trucks on an apparently endless supply of scavenged fuel and spare parts. But I'm positive exactly this Hollywood spirit is what fuels (pun intended) most of those hyper-optimistic answers.