Mark Fischenich: Ask Us: Roundabouts aren't just safer; they're healthier

Aug. 21—Q: This question randomly came to mind after that guy rammed through the roundabout the other day. A MnDOT study from 2017 found roundabouts in Minnesota reduced fatal and serious injury crashes at intersections by 80%, including zero documented multi-vehicle fatalities at roundabouts.

So roundabouts appear to be safer than traffic-light intersections, but are they also considered greener? By "greener," I mean more environmentally friendly in terms of car emissions. My impression is cars idling at stoplights would produce more overall emissions than relatively smoother flows of traffic at roundabouts, but it'd be fascinating to learn if that's actually the case, or if there's any real tangible difference between the two. Thank you!

A: Sometimes, when Ask Us Guy is poking around the internet hoping to find a quick answer to a question, he comes across a document that looks to be so perfect that he hears the angels singing. That was the case when he came across a research report titled "Quantitatively Determining the Emissions Reduction Benefits of the Replacement of a Signalized Intersection by a Roundabout."

Then he looked at the date and saw the study was 2007. Then he noticed the research wasn't done by the Federal Highway Administration or the Environmental Protection Agency. And it wasn't done by a scientist at an acclaimed university. Or even by an adult.

It was done by Maxine Hesch of the Academy of the Holy Names, which — as it turns out — is a high school, and Hesch had kicked off her project as an eighth grader. But it actually is an impressive piece of high school science and found that a roundabout in Rotterdam, New York, reduced various vehicle emissions by anywhere from 16.36% (nitrous oxide) to 26.05% (hydrocarbons) compared to a traffic signal because of reduced vehicle idling time.

Ask Us Guy kept looking and found a more recent (2021) study published in a scholarly journal dedicated to the impacts of transportation on the environment. It looked at replacing stop signs with roundabouts and came to the same general conclusion as Hesch. The study also determined the environmental costs of converting an intersection from stop signs to a roundabout — adding up all the emissions from creating the construction materials and running the heavy equipment — was quickly offset by the reduced emissions from vehicles once the roundabout was in use.

"The case study estimated that converting 72 stop signs to roundabouts within El Paso, TX, reduced daily vehicular CO2 emissions by more than 50 tonnes, paying back the CO2 from construction and maintenance within 2.5 to 2.9 years," according to the report titled "Regional CO2 impact assessment of road infrastructure improvements."

And a 2018 study in the Journal of Transport and Health found that city dwellers could breathe easier if roundabouts replaced signalized intersections. At least in certain places, roundabouts can reduce PM2.5 pollution — the especially fine particulate matter from vehicle exhaust that can penetrate deep into a person's lungs — up to 40%.

"As planners and policy-makers propose roundabouts to relieve congestion and improve safety, this research provides additional evidence that the benefits of doing so can extend beyond the immediate intersection in certain communities; particularly when a community simultaneously installs roundabouts at all of its failing signalized intersections," the report concluded.

So, in summary, roundabouts are greener than stoplights. And Maxine Hesch rocked that high school science project 15 years ago.

Contact Ask Us at The Free Press, 418 S. Second St., Mankato, MN 56001. Call Mark Fischenich at 344-6321 or email your question to mfischenich@mankatofreepress.com; put Ask Us in the subject line.