Let me correct what appears to be a miscommunication.<p>The numbers I gave don&#x27;t prove anything, other than show that there is a huge range in cost, depending on the intersection type. You say &quot;the lights, cameras, and network connections are already installed and paid for&quot;, but how many intersections are that way?<p>More specifically, the numbers I showed are that a fully equipped signal, like what you want, costs $450,000, while a roundabout is cheaper. If all lights already have &quot;lights, cameras, and network connections&quot; then it&#x27;s a sunken cost. If 1% of the signals are that way, then it&#x27;s entirely different.<p>I certainly don&#x27;t know how interconnected the lights are. But even with hard numbers - and you haven&#x27;t made any claims to any numbers - that&#x27;s only a part of the point. (FWIW, the best numbers I found are from <a href="http:&#x2F;&#x2F;readwrite.com&#x2F;2014&#x2F;01&#x2F;22&#x2F;ai-traffic-lights-intelligent" rel="nofollow">http:&#x2F;&#x2F;readwrite.com&#x2F;2014&#x2F;01&#x2F;22&#x2F;ai-traffic-lights-intelligen...</a> which says &quot;According to el-Tantawy, many of today’s traffic lights at intersections operate based on pre-programmed repeated cycles that run with little or no input from fluctuations in traffic.&quot;. That&#x27;s not really helpful, other than to show there are a lot of dumb signals in the US.)<p>Yes, <i>construction</i> is cheaper <i>on average</i> for signals, but bear in mind that signals with &#x27;lights, cameras, and network connections&#x27; are definitely not average signals.<p>But construction is only part of the cost-benefit analysis. The signals need to be powered, and replaced about every 10 years according to one of the URLs I gave. Roundabouts have a 25 year lifetime. Roundabouts are also safer, so there the benefits to human life must be included. And as I pointed out, you also have to consider the failure modes.<p>Sure, yes, there&#x27;s &#x27;low hanging fruit&#x27; (which is a misnomer, as the really &#x27;low hanging fruit&#x27;, like traffic light coordination and in-pavement detectors, have long since been picked). But that&#x27;s because you have a goal in mind, which is to &quot;improve traffic signals&quot;, not &quot;improve traffic systems&quot; (which roundabouts do), or &quot;improve quality of life&quot; (which &#x27;complete streets&#x27; and livable community advocates want to do).<p>Thus, if you think that &#x27;&quot;The reductions of 40 percent in vehicle wait time, nearly 26 percent in travel time and 21 percent in projected vehicle emissions realized in this pilot are remarkable,&quot;&#x27; is a good justification, then you have to compare it to <i>other</i> solutions which achieve or improve upon those same goals, and not just cherry-pick (again with the fruit metaphors!) the numbers that best support your goal.<p>As I also pointed out, the pathway to more roundabouts isn&#x27;t to wholescale replace existing signals, but to use them for new intersections, and for those with high accident rates where it&#x27;s most worthwhile to switch. The over time, as the old signals need replacing, switch many of them to roundabouts.<p>That too &quot;would substantially improve things, even without an AI&quot;.