This argument always seems a little strange to me. I think I can count on one hand the number of times, in 14 years, I've ever made eye contact with another driver while driving, or used some kind of hand signals. And in all of those cases, if the signaling had failed, the situation would have resolved itself just fine in less than a minute anyway. Most of the time, I can't even see the other drivers through reflections on their windshields. Sure, sometimes I'll stick an arm out the window to wave my thanks when somebody lets me merge, but that's not a critical communication.