I understand that cars serve a purpose. But trains and buses move orders of magnitude more people than cars could ever dream. With a properly functioning transit system (including the aforementioned high speed rails) traffic would clear up (because traffic didn't happen to you, you are traffic), and fewer distracted operators would be on the road.
And in removing those people from operating vehicles, the distraction of a billboard, and the subsequent potential accidents, are mitigated.
Have you considered a conversation with someone like Lina Khan? Even if it's just to get you talking to the right people in government. I love this!