I'd wish new construction aimed for that, but converting existing four-way stops to roundabouts would require widening of the road at all four corners which is

I'd wish new construction aimed for that, but converting existing four-way stops to roundabouts would require widening of the road at all four corners which is impractical (i.e. you may have to knock down buildings, but certainly have to re-place sidewalks). The data shows that roundabouts are safer and even improve traffic flow. But they're also a nightmare to install after the fact, which is why it is so uncommon. All we can do is stop making the same mistakes going forward. Same thing with burying power lines: Far cheaper to do with new construction, substantially more reliable and better able to withstand natural disasters, but we aren't. Society is just bad at planning for tomorrow if it costs us a little today at every level.