How many people would actually know to try the AM band in an emergency? How many people even still know how to turn their radio to an AM band? And know what station to listen to?

I think this number is waaaay smaller than anyone thinks. Especially with modern buttonless car systems.

Where I am in Mass, highways often have big billboards saying "Tune to 1610 AM for emergency info" or whatever.

This is common in mountains in WA too.

To replace the AM in cars isn’t just the cars - it’s all the signage and transmitters, for regional information.