There might be something different in these. This is just a feeling and nothing that I could say with any assurance is correct. But the attara from may mean "If I had a car..." whereas the areba form could mean "If there were cars..." I don't know about the last one. I mean, even if you can say that.

I think that the difference is in the use where the tara ending is " ... if you had" or " ... if you do (something)" Well, anyway good luck -- the library is closing.