The metric system makes it easier to divide by ten (which you could do anyway without changing your units) at the expense of making it impossible to divide by three.

Yes John, traffic circles do slow down traffic, most need to be larger and need an extra merge lane around the outside with enforced alternate merge.

Four way stops are not too good because some of them are not marked as such; this means that any stop sign could be a four way stop, and the knowledge of your right of way is dependent upon a sign that is down another street (and you can only see it edge on, if at all). I still think that it is a better idea to just slow down the traffic instead of stopping it completely.

Bill, there was a town in Germany recently that removed all traffic signs. They found that drivers behaved more politely and there were less accidents. Probably needs more study though.