Idea for an App: Will Humans Talk to One another Through Cars?

Here's an idea for an app -- if not already though of -- one where you can send written or oral messages to other cars on the road that have also downloaded the app. Or even people in your proximity. The logical next step beyond Waze.

Or imagine a cross between CB and Waze. One where you voluntarily, directly send messages to cars where you can consent to either identify yourselves or remain anonymous.

Has someone already thought of this (usually when I get a Eureka moment, I find out, alas, someone has)?