Actually, now that I think about it, the only time we had a real Emergency Broadcast Alert here in the Bay Area was during the big quake of 1989. All radio stations went off the air except the two authorized to broadcast during an EBA. We have had a few alerts for storms, fires, etc, but those were warnings, not emergencies. I wonder if the rules have changed for EBA?
In some markets (areas), some radio programming might be available only on AM.
Boston, MA is SOMEWHAT an example. WBZ (AM) is known for its comprehensive traffic reports updated every 10 minutes. I think WBZ might simulcast on an "HD" channel on FM, but I have not driven a car that can receive that. So *my* only option in a car is to hear them on an AM radio. Would FM stations pick up the void if AM radios disappeared? Doubtful.