It seems to me that the whole "save AM in cars" movement is predicated on a world that simply doesn't exist anymore.
There are almost no "white areas" (no local FM service) left in any populated part of the US. Whether you're in McGrath, Alaska (hi, Paul!) or Dyer, Nevada, there's something available to you on FM.
There's nothing magical about AM transmission in an emergency situation these days. I can throw a Gates GX or a Nautel VX kilowatt rig in a travel case, rig up an antenna and be on the air on FM just as fast, if not faster, as I could rig up a longwire and get on AM.
The typical FM site these days is a lot newer and more robust than an AM site, which can often be 80 years old or worse and usually suffering from long-deferred maintenance.
Everything else is imagination, myth and nostalgia. Sure, the FCC *would* let you keep an AM on with day power at night in a massive emergency, but what AM station is actually going to do that in 2023? When was the last time any AM did that? I literally cannot think of a single 21st century example of a station using that authority, and I've been reading FCC filings every day since before the turn of the century.
What kind of emergency would wipe out every FM signal in an area and still somehow magically leave an AM standing - and one that would magically have the resources to provide live emergency coverage to whatever listeners still have AM radios? It literally HAS NEVER HAPPENED in this century, or even in the last 20 years of the last century.
Skywave at night? OK, sure - but that doesn't help you in a daytime emergency, and in any event, if northern Arizona is somehow wiped off the face of the map, what AM skywave signal is going to drop what it's doing to provide targeted coverage to somewhere far outside its market? KNX? KCBS? It doesn't help that the company that is the dominant owner of news AM signals is also teetering on the brink of bankruptcy.
I'd like to see the proponents of the save-AM-in-cars movement point to even a single example of an emergency situation where AM radio was the exclusive source of emergency information to an affected area.
Hasn't happened, doesn't happen, won't happen.