I didn&#x27;t say &quot;all&quot;, I said &quot;most&quot;. Even countries with roundabouts also have traffic signals.<p>My comment was not trying to establish what you are asking for. Instead, I was pointing out that there are many factors in addition to &quot;cost to replace&quot;. There is also the yearly upkeep costs (power to the light, landscaping), signal timing maintenance every few years, and a shorter lifespan for signals vs. roundabout.<p>Plus, of course, the savings in human time and lives.<p>Then there&#x27;s systemic issues which are harder to quantify. Roundabouts have higher throughput than signals, so switching to a roundabout might reduce the need to widen nearby parallel roads, which is an indirect cost savings. And roundabouts without signals work even when the power goes out.<p>Quoting from <a href="http:&#x2F;&#x2F;www.roundaboutresources.org&#x2F;when-should-roundabouts-replace-traffic-signals.html" rel="nofollow">http:&#x2F;&#x2F;www.roundaboutresources.org&#x2F;when-should-roundabouts-r...</a> :<p>&gt; Roundabouts give superior traffic and safety performance to signalized intersections and to cross intersections almost everywhere, but roundabouts cost more, and not every signalized intersection or cross intersection is in great need of correction. Therefore, a highway agency should start at the top of its high-crash list and its high-congestion list and work down, often converting the problem location into an offset intersection where crossing flows are not too high. ...<p>&gt; The modern roundabout should be recommended not only as a retrofit where there are present safety and capacity problems, but also as an intersection in new construction where roads join or cross each other for the first time.<p>That seems eminently reasonable to me.<p>Recall too that the challenge was to &quot;devise a traffic light that would not be monumentally inefficient and incompetent&quot;, so the question is, how much would that hypothetical system cost per intersection, vs. a known, good solution to the given problem?