This reminds me of a documentary I saw about the fall of Saigon. When the SHTF, Americans and selected Vietnamese were supposed to hop on special buses and go to the airport for evacuation.
It never occurred to anyone that the roads are impassable once the SHTF.
All Americans got out but many of the select Vietnamese were screwed. The signal for Americans to get out was the American Radio Service* played “White Christmas.” This was at the end of April.
*Successor to AFVN.