How can I stop my dog from "going crazy" in the car for Bikes, Trucks, Buses

When I take my 3 yr old Lab/boxer for a car ride, she barks like crazy when she sees a cyclist or a large vehicle...mainly trucks and buses...she does stop if she is told but, will start up again when you least expect it...We havent tried leashing her to the seat buckle because she would be unconfortable.....any ideas?

Right now the energy from the vehicles - mixed with her desire to protect her car and everyone in it is driving her to get frenzied.
It would be good to teach her the 'leave it' command and help her stop the behavior by catching her before she barks. Let her know that the barking is no longer an option and reward the heck out of her when she is quiet when someone buzzes by. Have her on the leash so you can enforce your words, but best to not even let her get to the barking frenzy at all.
You need to go and park near a busy street and stay there until she falls asleep with boredom.

Thank you for your help....I will let you know how it works...Im sure she'll calm down...I just needed some guidance!