That varies by location. In Baltimore the news radio with traffic and school closings is AM but in DC it is FM.
Update: the Baltimore AM station also is on FM. The DC news station has three on air stations in the metro area including Warrenton VA and Frederick MD.
About every state hss up to date road conditions on line at their dot site. If you go to safe travel.com you can select the state you want. Some even give you the dash cams from the plow drivers so you can see for yourself. For traffic though or hazards up ahead, it’s Waze. Like the pireps for pilots except drivers. Can’t look at your shone though while driving.
I can’t watch dash cam video of other drivers while I drive to work, I would rather listen to the radio.
Someday I might buy a used car, modern vehicles with HD Radio can show traffic and weather on the display screen.
I listened to AM radio growing up, because that’s all there was. My father listened to FM classical music, but there was no popular music or sports on FM, then. Once all that moved to FM, so did I because the quality of the sound was far better. And the AM radio on my 53 Buick was pretty powerful, but it took a while to warm up and the headlights dimmed a bit when I turned it on. Now people stream things with their phone linked to the car’s audio system. It’s not a conspiracy, it’s people wanting more and more choices.
Yes, NJ’s 511.org is very useful in that regard–before I leave home. But, as you stated, that isn’t very practical to do once you’re on the road. That’s when I sporadically listen to an AM station for traffic reports.