I think that's the key. In person, you're somewhat accountable for how you act. Rudeness doesn't usually pay off; there are social checks and balances. But in your car on the road, it's a whole different story. Unless you do something flagrantly illegal or dangerous, you can be as rude as you want, and most likely you won't see any consequences; you're dealing at a safe distance with strangers who you will probably never meet face-to-face. How a person acts when they feel anonymous is probably a truer measure of their character than how they act around people they know.

Do morals hold when they're not enforced? Sadly, I think many people would answer this question differently in their heart of hearts than they do on a regular basis with their behavior. I wish I could exempt myself fully from this criticism.