Photo Clearwater MR by Ken Sides

The Innovation of Modern Roundabouts

Have you ever wondered about traffic circles, like really geek-out wondered what they accomplish? Well, Ken Sides has spent some of his career studying and perfecting the Modern Roundabout. Ken was gracious enough to take me to lunch to teach me about them. In fact, I even had homework to do to complete my education. And it was fascinating.

First, you need to make the distinction between traffic circles and Modern Roundabouts (MRs for this blog). The iconic traffic circles-think Arc de Triomphe, or DuPont Circle, are nothing like Modern Roundabouts.

MRs eliminate sixteen deadly crash points. Graphic by Michael Wallwork, P.E.

Here’s what I learned, and why I am a now a great supporter of the Modern Roundabout:

  • Modern Roundabouts are compact, taking far less real estate than their obsolete traffic circle predecessors.

  • While MRs are low speed, they typically increase capacity and throughput by 30% during peak times, and even more during off peak times. Hard to believe, right? Amazingly, their slow speed increases capacity because more approaching cars can slip into smaller gaps in the slow circulating traffic.

  • The incidence of fatality and severe injury is greatly reduced through the use of MRs. FDOT and the Federal Highway Administration report that fatalities drop by 90%, and all  injuries by 76% when MRs replace standard intersections. Consider the economic impact of reducing fatalities and severe injuries—the economic cost of a fatality is estimated at $10.1 million, and severe injury at $818,000!

  • MRs require no electrical power. This may not sound important, but consider power outages due to hurricanes, and all of a sudden that benefit becomes huge.

  • MRs have green impact- since cars are not stopping and starting as much, they emit less exhaust.

  • With pretty, landscaped centers, MRs add to the ambience of their surrounding areas. In fact, their landscaped centers add to their throughput efficiency, as well as safety.

  • MRs have far fewer points of conflict. As you enter a MR, the only direction you need to watch is that off your left shoulder. You’re not even distracted with the cars entering opposite you as they are obscured by the pretty landscaping. Brilliant!

Keck Circle roundabout in Vermont by Dan Burden

And on to the Homework! There’s nothing like experiencing MRs for yourself under the tutelage of the master. So, Ken suggested I drive with him and visit a few of Tampa’s MRs where I learned even more.

  • MRs are friendly. Many motorists waved at us as we stood to the side watching the traffic. When does this ever happen? I loved it.

  • You feel like you’re going really, really fast when you’re only going 14 mph. Seriously. This is because MRs are built with negative super-elevation. Right. What the heck does that mean? It means that the MR banks in the opposite manner. Consider a race track turn- the driver side of the car is the lowest point in the curve structure. In a MR, the driver side of the car is at the highest point of the curve. This alternate driver position makes you feel like you’re flying. Try it for yourself. I’d never have believed it.

Want to learn more about MRs? Here’s a presentation by Ken.

Ken Sides, is licensed as a Professional Engineer (PE), certified as a Professional Traffic Operations Engineer (PTOE), and accredited by the Congress of the New Urbanism (CNU-a) and a Senior Transportation Engineer at Sam Schwartz Engineering on Rocky Point in Tampa. Engineer of the year 4 times, 2004, 2008, 2011 and 2014, Sam was instrumental in 40 modern roundabout construction and has more than 25 years of experience. Follow him on Linkedin! Here’s an example of one of his projects.