Our biggest hurdle when out for a walk with Ellie is her wanting very badly to chase cars. She lunges, barks, growls and acts like a nut when a car goes by. She has gotten a lot better about this over time, however, I have noticed something about her. If she is actually walking when a car goes by, she gets anxious and acts nuts. When she is sitting, or asked to sit when a car goes by, she is calm and really pays little attention it goes by. She is gotten to the point now that she sits when she sees a car coming. I am wondering if she is calming herself? Could this be it or do you think she anticipates being put into a sit and is just beating me to the punch? We have worked with her to "leave it" and "watch me" and keep walking when a car goes by and we have also have had her sit when a car goes by, so it's not like we ask her to sit each time a car goes by. We mix it up. Obviusly if sitting keeps her calm when a car goes by, would it be such a bad thing to just let her do that ?

He will sit like a champ, and continue barking. (Not to disagree with your point, just had to add that since I was very surprised that it didn't work for him!)
I did see him get all four off the ground in a bark the other day though