Rise of the roundabout: Design favored by engineers at more and more intersections
Traveling Hargis Parkway from Radio Drive to HealthEast Sports Center and East Ridge High School, drivers pass through as many as six roundabouts. Fifteen years ago, the roundabout design may not have even entered local engineers' minds.
The first of 16 roundabouts in Woodbury opened in 2005 — and six were constructed in 2008 alone, alongside the opening of East Ridge High School.
Those particular loops were designed with the high school — and its accompanying teenage drivers, bikers and walkers — in mind, as roundabouts offer a "calming effect" on traffic, Woodbury engineer Tony Kutzke said, by slowing speeds to 20 miles per hour or lower.
The slower speeds required to enter a roundabout can help prevent serious crashes.
The roundabouts along Hargis Parkway were added as similar designs were embraced for roads elsewhere in the southeast metro. The alternative to traditional four-way intersections has continued to be used in existing road upgrades and new construction throughout the area.
Minnesota Department of Transportation studies found that fatal crashes decreased by 89 percent, a 74 percent decrease in crashes that result in injury and a 39 percent decrease in all crashes when an intersection is converted to a roundabout.
It not only slows drivers down, but removes the risk of a T-bone collision, or 90-degree collision, the most severe kind of crash.
"They reduce the severe types of crashes at the right locations," Washington County Traffic Engineer Joe Gustafson said.
Roundabouts are not a cure for all collisions, just the right ones, Dakota County Traffic Engineer Kristi Sebastian said.
"Some of our roundabouts have more property damage, (but are) better at preventing fatal and serious injury crashes," she said.
When collisions do occur in roundabouts, Sebastian said, it's because drivers are not yielding to all lanes or traffic, entering the roundabout without yielding, choosing the correct lane or crossing lanes improperly.
There was a bit of a learning curve when Dakota County started implementing roundabouts, Sebastian said, especially when it came to the multi-laners. About 10 years out from their first county-built roundabout, drivers are far more used to taking the curve.
"There's definitely decline in those collisions from some of those typical errors," Sebastian said.
Gustafson said the real telling point is that rather than county staff having to defend their decision to install roundabouts, in many cases they now have to justify why they aren't using one.
"People who tend to be more vocal are the proponents," he said. "Five, 10 years ago it was the opponents."
Kutzke said as they became more standardized across the country, cities such as Woodbury gained "confidence in them as a tool." Once staff became comfortable with them, and drivers became comfortable with them, there was a lot of positive feedback.
While the British have been using roundabouts in their roadways since first creating the modern roundabout in the 1960s, American engineers weren't comfortable with it until 1990, when one was built in the deserts of Nevada.
Twenty years later they could be found in every state, with over 3,200 built by 2013.
MnDOT latched onto the trend in 2002 when it constructed its first. A handful had been built by cities and counties prior.
Brooklyn Park and Farmington were a little before their time, building roundabouts in 1995 and 1997, several years before the state had devised their first.
The roundabout in Farmington — a picturesque loop found at Spruce and 12th streets — was specifically constructed as part of a development, as a trendy bit of engineering in a unique residential development.
There were 140 accounted for across the state when the MnDOT stopped keeping track in 2014. Gustafson predicts there are now between 200 and 400.
Hastings notably lacks the roundabouts most other cities in the region boast, but not because the city is anti-roundabout, Public Works Director Nick Egger said.
Because "traffic patterns are kind of stagnant," Egger said, they don't have a reason to modify any intersections at this time.
"It would be in the mix if we ran into an applicable situation in the future," Egger said. "We're probably a little way from having that conversation."
When building or reconstructing an intersection, the state requires that engineers consider each type, including roundabouts, to ensure they've chosen the most effective solution at each location. Their decision is based on a number of factors, including drainage, road construction schedules, safety and traffic flow.
Roundabouts often move traffic through more quickly than lights or stop signs. Gustafson said even during peak traffic times, roundabouts can be more efficient.
"At a roundabout, you're always going to have to slow down, but ... it processes traffic more efficiently," Gustafson said. "It's less of a roll of the dice than the lights."
This high efficiency really depends on what Gustafson calls "conflicting volume."
If there is a significantly greater amount of traffic on one road in an intersection, it may be more efficient to have a longer green on the more densely traveled road. However, if both roads have a high volume, the roundabout will boost efficiency.
As communities such as Cottage Grove continue to grow, intersections must be updated to take on the increased volume, Cottage Grove City Engineer Jennifer Levitt said, and increasingly, that solution is the roundabout.