For what it's worth, having the tracks and the car lane together is very prototypical at least where I live. So, maybe the one way idea is a good solution. Or, have the car lane go the other direction and just don't have cars on the lane in which the streetcar runs.
On my layout, I have some old abandoned train tracks buried in cobblestone that run through the town and now "car traffic" uses that road. Sort of the same idea in reverse, I think.
