What do you do when someone lets you break in traffic?

This morning I had to yield to a steady stream of traffic. I was prepared for the long haul of waiting for a quick break, but a kind soul waved me on to my destination. She was actually smiling. I say that because I've had people with irritated looks on their faces wave me on. It's almost road rage during an act of kindness! Anyway, I waved my thank you back to this nice lady. But other times this happened to me, I felt like it wasn't enough to just wave. So now when someone waves me on~~~I say a prayer for them. And I hope they feel it for the rest of their day.