SIMPLICE! SIMPLICE! TOJOURS LE SIMPLICE!

For years, I've groused about overdesigned rotaries.  "The point of rotaries is to simplify traffic flow, and it defeats their purpose to provide multiple lanes."  My gripe is impressionistic, based on my frustration with Wisconsin's penchant for slip lanes and overhead signage.  "Too much nuance in the construction of a rotary defeats its purpose."  Consider, dear reader, when among all the government follies to mock on April Fools Day, the Wisconsin rotary gets dinged.  "Overdesigned rotaries make motorists mad, so much so that Right Wisconsin posted an April Fool capturing the spirit in Wisconsin, a state notorious for overdoing the channeling and signage of the rotaries."

The good news is that Charles "Strong Towns" Marohn has the traffic engineering expertise to ask the Credentialed Experts to reconsider.  "A dangerous Minnesota roundabout shows what happens when engineers preserve future traffic capacity at the expense of safety today."  For "dangerous," read "overdesigned."  "This story ends with drivers being blamed for failing to navigate a design that engineers have spent more than a decade trying (and failing) to make understandable, and engineers continuing to deprioritize safety, in spite of recent policy directing them to make it their first priority."

But it's all with The Best of Intentions.  (Isn't it always?)

The intersection of Kenwood Trail and 185th Street West sits about a mile east of Interstate 35 in Lakeville, Minnesota. It was converted from a signalized intersection to a full two-lane roundabout in the fall of 2015, with two lanes entering, circulating, and exiting in all four directions.

The original signal struggled with growing traffic volumes, creating backups and a pattern of crashes that local residents remember as less frequent, but more severe. The roundabout was intended to keep traffic moving while replacing high-speed, right-angle conflicts with slower, less severe collisions. Because the design was unusual in Minnesota, researchers from the University of Minnesota began observing it almost immediately after it opened.

Now, amid an increasing number of crashes following more than a decade of study and modification, officials are considering everything from still more signs and markings to removing the roundabout and reinstalling the signals it replaced.

Is that really the only option left?

I'm not sure what "existing signal struggled" means, the crossing in question looks much like almost any crossing of section roads in Chicago's suburbs, which tend to have one or more dedicated left turn lanes with a controlling arrow and sometimes a slip lane for right turns, perhaps with a turn arrow, and any pedestrians in the area long since have given up on walking or relocated to Wrigleyville.

Because two lanes in each direction crossing two lanes in each other direction, some Bright Spark got the idea to provide two lanes around the roundabout.

Roundabouts achieve safety by slowing traffic and simplifying the decisions drivers must make. A single-lane roundabout eliminates high-speed crossing movements and asks drivers to do something relatively intuitive: slow down, yield to anyone already circulating, enter when there is an opening, and exit at the appropriate point.

The Lakeville roundabout compromises that simplicity in the pursuit of capacity. It has two lanes entering, two lanes circulating, and two lanes exiting in every direction. Drivers must choose the correct lane before entering, understand which movements are permitted from that lane, track the vehicle beside them, and anticipate whether a vehicle in the inner circulating lane will continue around or exit across their path. This is all done with generous, sweeping curves, forcing a driver to perform a lot of situational analysis at what are relatively high speeds.

That's asking for trouble, because somewhere around the circle a driver in the inner lane has to get to the outer lane to continue, or wind up like Homer Simpson trapped forever in Paris traffic.

Drivers were much more likely to pull in front of vehicles traveling in the inner circulating lane.

That pattern makes sense. An entering driver sees a vehicle in the inner lane and assumes it will continue around the circle. The circulating driver may instead be preparing to exit across the entering driver’s path. This is a known, common point of failure; the same misunderstanding appeared at other two-lane roundabouts included in the study.

The researchers then examined the standard engineering responses to this repeated failure: signs, pavement markings, extended solid lines, overhead lane designations, and changes intended to make the proper movements more obvious. Some treatments reduced certain improper turns. None solved the central failure-to-yield problem. The MnDOT report ultimately found no successful intervention that meaningfully corrected that behavior.

That should not be surprising. The problem is not simply that drivers lack information. The multi-lane design requires them to process too much information at once, especially when speeds aren’t dramatically reduced.

A single-lane roundabout reduces conflict by removing choices. A two-lane roundabout restores those choices so the intersection can move more vehicles. The additional lane does not merely add pavement. It adds ambiguity about where drivers are going, who must yield, and whether two vehicles can safely exit at the same time. The safety benefit a roundabout provides comes from simplification, but that benefit is lost when more lanes make the intersection complicated again.

After they've tried everything else, perhaps Minnesota will apply a little Yankee logic. "Make the roundabout one lane. Make it simple. Make it safe."

Undoubtedly, people will complain about having to merge before they enter the rotary, and complain about how long the wait is, but waiting your turn is what happens when there is traffic, whether it's to get into the rotary or for the traffic light to cycle through all the arrows.