Colorado Public Works Journal, Spring 2021

Spring 2021 | 11 about-first” policy in Colorado as well. He estimates he’s given his “Roundabouts 101” presentation to about 20 groups around the state as he pushes for their adoption. One of his clients was the town of Superior, where he helped install a few before leaving his consulting business in 2012 to direct public works. During his eight years in that position, four more roundabouts have gone in. He figures he’s been involved with “several dozen” across the state. The Colorado Department of Transportation estimates that about 140 roundabouts on the state’s highways have replaced traditional traffic signals or signs at intersections. Twenty-six of those have been constructed on or adjacent to state highways, including some that facilitate entry to or exit from interstate highways. Ben Kiene, CDOT traffic operations engineer for the region that includes Denver and surrounding counties, says that roundabouts have come to be regarded as one of the primary options for solving traffic problems across the state. “Whenever we have a major interchange project, a roundabout is usually looked at as one of the alternatives,” Kiene says, noting space constraints in urban areas can make roundabouts unworkable or, if they’d require a lot of property acquisition, too costly. “It's not necessarily that there's a designer preference or anything, it's that they're kind of in the mix.” Last summer, CDOT even produced a roundabout education video, a birds-eye-view animation of how different types of roundabouts work. “You don't have what’s called lost time at a signal,” Kiene says. “Every time the signal changes, during that ‘clear interval’ nobody is supposed to enter the intersection—so that's time that, with a roundabout, you have traffic flowing continuously. They're very advantageous that way. And they do have an injury-crash rate that is pretty significantly lower.” He adds that research has shown the average range is about a 70% reduction in injury crashes as a result of conversion of a conventional intersection to a roundabout. There’s some nuance to that—the number of lanes in the roundabout, which vary with traffic capacity at a given intersection, can have an impact on its safety performance. “When roundabouts first open,” Kiene says, “there might be a slight increase in property damage crashes that are mainly merely fender- benders as drivers get used to them. And then they drop off.” So what took Colorado—and the United States in general—so long to warm up to roundabouts? Brian Walsh, chair of the Transportation Research Board’s standing committee on roundabouts as well as an operations engineer at Washington state’s transportation department, says the reasons stem from the country’s decision, early on, to go all-in on traffic signals. “We just decided that was what we're going to do anytime we had an intersection issue from a capacity standpoint, or a safety issue,” Walsh says. “So consequently, I think we have 300,000-plus traffic signals in this country, and what was missed a little bit with that was the idea that you can build intersection control that was self- regulating and also was dirt cheap, meaning you didn't have to put anything out there, other than a circle. And the Europeans had figured that out.” Oddly enough, American designer William Phelps Eno largely gets credit for the invention of the roundabout. Built in 1905, Columbus Circle was his handiwork, though it doesn’t quite conform to today’s definition. Walsh notes that what was missing from that circular traffic pattern in New York City was one essential concept: the yield rule, which states that vehicles currently in the circular pattern always have the right of way. Meanwhile, in the 1960s, both the United Kingdom and Australia figured out that roundabouts using that simple rule of the road could maximize both safety and capacity. “Then we had a couple Americans give it a shot and said, ‘Hey, this makes sense. Why haven't we had more of these?’” Walsh says. “So now you have a culture that's very biased towards one thing—and the other thing looks like it's a foreign thing. It's an us-against-them type of thing that’s in play with two intersection-control devices.” Eventually, Walsh’s Washington state and about a half-dozen others became early adopters of the most recent wave. Colorado was in that mix—particularly locations like Colorado Springs, Vail and Golden. Still, those Colorado experimenters acted primarily on the municipal agency level to address specific problems. In particular, Golden stood out, in large part because traffic engineer Ariniello, its consultant on the project on South Golden Road through