Copyright Infringement in Traffic?

I wonder why blasting music over a car audio system, so loud that it can be heard (and often: felt) several lanes over, does not legally constitute a public performance.  If you play music anywhere else, it is deemed a public performance and qualifies for royalty compensation, according to the RIAA and the DMCA.  Ask anyone who runs a skating rink, doctor's office, or grocery store.  They typically pay a monthly fee to keep that Muzak crap pumping through your ears while you narrow down which cereal you're going to buy, or rinse and spit after your cleaning.

I know someone personally who used to manage a skating rink, who was visited by an attorney with papers ordering him to either stop playing his own music (his collection and his stereo system) or pay for each song played, along with keeping a play log.  His third option was to subscribe to Muzak.  The attorney was supposedly representing BMI/ASCAP, but he's probably paid by Muzak as far as I'm concerned.

So, the criterion is playing music for the "benefit" or "participation" of an audience?  Does that distinguish what constitutes an "audience"?  Is there a difference between an audience by "circumstance" (traffic) from "intentional" (parties, sports, recreation centers)? Or is there a clause that excludes cars as a source of the "performance"?

I can see it now, RIAA attornies roaming around in traffic, in the Summer, trying to hand out "cease and desist" letters to gangster kids in their tinted-glass BMW's and spinner-wheel Escalades.  Wow.  That would be a scene to watch.  How about they try to pull that off in Crenshaw, Watts or East L.A.?  Brooklyn, East Chicago, East Philly, and so on.  Where's Howie Mandel when you need him?  Personally, I would LOVE to see this.  I'm so tired of the bass thump beating my ear drums to death in traffic.  Country on the left, Rap on the right, Dance/Trance in front of me.  Oh well.

I have very little sympathy for "artists" and the RIAA.  MTV Cribs took care of my sympathy worries.  Apparently, all the piracy they talk about hasn't hurt the ability of artists to buy nice houses and fill them with nice stuff.  But loud, pumping "music" in traffic is one situation where I would probably applaud an army of RIAA attornies swarming in to issue legal warnings.  I guess I shouldn't hold my breath.