A search of the keywords "china evacuate million typhoon" yields many hits.

The Lunar New Year migration in China has several individual train stations seeing departures of over a million people over a few days. Change "departures" to "evacuation" and I see no reason they couldn't do a million+ population city.

The problem is translating those lessons to the US. Thanksgiving is the biggest migration in the US but I suspect there's a long period of behind-the-scenes preparation work in getting fuel & supplies pre-positioned for airplanes and cars. I doubt it would be possible to repeat that without a month or more or lead time. Ans the US doesn't have a train infrastructure that is useful for such a problem.