Bulldog, congrats on handling the situation so well! It wouldn't have done any good to yell at the other driver or threaten him, and could have caused additional stress for your wife and daughter.
The reality is that living in the greater DC area is stressful and traffic is horrendous. I've reached the point where I avoid shopping on Saturdays entirely. I've started going to the grocery store, pharmacy, or whatever after dinner on the weeknights. It's not fun after a full day of work, but it is saving my sanity. I also order as much through Amazon as possible.