You need to work on desensitising her, start further away from the road at a point where she barely reacts to the cars and do as you have been doing, reward good behaviour and distract from unwanted behaviour.

Slowly get closer to the road as she becomes less reactive to the cars continuing to reward and distract. It might take a while but it will work if you're consistent and patient. [/QUOTE]

The only trouble I can see from this approach is that it's very easy for someone to be unintentionally rewarding the excited behaviour, if they don't read the dog properly.

I always think that if you take the dog to the situation and act on it there and then, the dog will have a clearer idea about what your disagreeing with. I am no professional though...