How to give back

I have seen people complain in letters to the editor when they let someone into traffic, and the person doesn't wave their thanks.  To tell the truth, before I read these letters, it never occurred to me that it was expected, whether I was the giver or receiver of the favor.  But now, I try to wave when someone lets me in (at least, as soon as it's safe to take my hand off the steering wheel).  For myself, it is more important to me if I do people the favor of letting them in, that they pass it on to others.

On the way to my present work, there is an intersection where we are normally backed up both ways.  My lane has the right of way, but is going very slowly.  It is really nice to see that most of the people in my lane will let someone in from the side road.