How to Convert a Four-Way Stop to a Roundabout

If you've got an intersection with four stop signs, it will be cheaper to build a roundabout. That's because of all the traffic light costs that Zachary Crockett told us about. But what if an intersection already has traffic lights and you want to convert it to a roundabout? Brainerd says this easily pays off in the long run, but in the short run...