If built, this proposed roundabout at Mankato Avenue and Highway 61 in Winona may see more traffic than any other roundabout in the state. The traffic load is still within the range two-lane roundabouts are designed to handle, and there are busier roundabouts elsewhere in the Midwest.

Hwy. 61 roundabout could be MN’s busiest


(7/29/2020)

by CHRIS ROGERS

 

The proposed roundabout at Mankato Avenue and Highway 61 in Winona may be the busiest roundabout in Minnesota, according to state records.

A 2017 Minnesota Department of Transportation (Mn/DOT) report detailed 144 roundabouts in the state, the most comprehensive recent study. The intersection of Mankato Avenue and Highway 61 is 27-percent busier — as measured by average daily traffic (ADT) — than the most heavily traveled roundabouts in that report. Mn/DOT officials could not point to a Minnesota roundabout with more traffic.

Mn/DOT Project Manager Chad Hanson acknowledged the proposed circle at Highway 61 and Mankato Avenue would be one of the busiest roundabouts in the state, but pointed out that the traffic loads at Mankato Avenue and Highway 61 are well within the range two-lane roundabouts can handle. He also noted that ADT is a simplistic look at the intersection and more detailed traffic analyses show a roundabout will work better than the current stoplights — reducing both congestion and serious crashes. “We’re confident it’s the right solution,” he stated.

Roundabouts have been gaining popularity across the country for their ability to simultaneously relieve congestion, reduce serious accidents, and improve pedestrian and bicycle safety, according to state and national studies. “The traffic performance is just better with the roundabouts,” Winona City Engineer Brian DeFrang said.

Some Winonans are skeptical of Mn/DOT’s plan to build four roundabouts on Mankato Avenue. City and Mn/DOT officials have, at times, characterized that sentiment as a resistance to change or a fear of the unknown. Other Winonans offered more nuanced critiques, saying three out of the four roundabouts might work, but Highway 61 is too hectic. Winonan Jack Stoltman asked at a public forum this spring, “Have they seen this somewhere that’s this busy and it’s worked?”

 

Busiest in Minnesota, but not the Midwest

The intersection of Highway 61 and Mankato Avenue averages 36,200 vehicles a day, according to Mn/DOT traffic counts. Minnesota’s busiest existing roundabouts are in Forest Lake, Cottage Grove, and Mankato, with ADT counts between 28,175 and 28,500 vehicles per day, according to Mn/DOT’s 2017 roundabout study and ADT records. That makes the Winona intersection more than 25-percent busier than the most heavily traveled roundabouts in the state, according to available data.

The 2017 study did not include every last roundabout in Minnesota, and its author acknowledged there is no comprehensive list. It is also possible that busier roundabouts have been built in the state since the 2017 study. Mn/DOT District Six officials said they were not familiar with what roundabout is the state’s most heavily traveled. However, all of the roundabouts they offered up as comparable to the Winona intersection — intersections in Forest Lake, Richfield, Woodbury, Mankato, and Cottage Grove, Minn. — fell at least 7,700 vehicles per day short of the ADT at Mankato Avenue and Highway 61.

While the North Star State doesn’t appear to have any existing roundabouts that rival it, the traffic load at a Mankato Avenue and Highway 61 circle would be far from unprecedented. A roundabout in De Pere, Wis., gets 34,700 vehicles per day, according to Wisconsin ADT records. In New Berlin, Wis., a roundabout near Interstate 43 tops 43,000 vehicles per day and another roundabout in Dublin, Ohio, sees nearly 47,000.

The Federal Highway Administration recommends that single-lane roundabouts are suitable for up to 25,000 vehicles per day and two-lane roundabouts — like the one proposed at Highway 61 in Winona — can handle up to 45,000 vehicles per day. “I think the key takeaway is we’re still significantly under that 45,000,” Hanson said. “No matter what numbers we’re looking at, if we’re well below that, that would tend to show [the intersection of Mankato Avenue and Highway 61] is well within the capacity of a two-lane roundabout,” he added.

 

Mn/DOT: ADT is a rudimentary tool

There are many ways to measure how busy an intersection is, and ADT is a very simplistic one, Hanson said. “That’s the starting point,” he stated. Engineers use ADT in the early stages of planning — a quick, rough guide to whether a roundabout is likely to work before they spend more time on more detailed analyses.

ADT counts average the total traffic load in a year to come up with a single number. Truly understanding how a roundabout would function at a given intersection is far more complicated, Hanson said, and requires looking at the traffic load for each leg of the intersection, how many vehicles are turning right, how many are going straight, and how many are turning left, and what the peak traffic loads are during rush hours. Mn/DOT has done that, developing a computerized simulation — imagine SimCity — for how traffic would flow through Mankato Avenue and Highway 61 with a roundabout versus stoplights. ADT is one number. Traffic models crunch pages and pages of data. “There’s hundreds and hundreds of variables that are within these models,” Hanson said. “Our consultant — they actually spent months on these traffic models,” he explained. Those computer simulations are also tested against the real world — to check how well they predict what people actually do at the existing intersection — and calibrated. “It’s a much more in-depth look at all of the dimensions and all the factors that would come into play here,” Hanson stated.

So Mankato Avenue and Highway 61 is well within the ADT range where a roundabout would be expected to perform well, and more importantly, detailed traffic analyses have borne that out — showing that a roundabout would reduce congestion compared to stoplights because cars wouldn’t have to wait so long at red lights, Hanson said. There will be lines to enter the roundabout during rush hour, but they have shorter waits than the current intersection, he stated.

 

Mn/DOT: Current intersection has a safety problem

Mankato Avenue and Highway 61 may be one of busiest roundabouts in the state, but it’s also one of the busiest signalized intersections in the state, Hanson stated. That high volume of traffic creates problems for the existing stoplights, too, he said.

During rush hour, motorists sometimes have to wait through two cycles of the stoplights, lasting up to six minutes in total, just to turn left, Hanson reported. As an alternative to a roundabout, Mn/DOT considered keeping the stoplights and adding double left-turn lanes to better handle all that traffic. However, that would force the state to make the intersection even wider — 150 feet wide on Highway 61 — and harder for pedestrians and cyclists to cross. It would also introduce more potential conflicts for motorists, Hanson stated.

As it is, Mankato Avenue and Highway 61 is the second-worst intersection in all of Southeast Minnesota for high-cost accidents, with 120 crashes in 10 years, including 41 injury accidents and two fatalities, according to Mn/DOT. “Obviously, there are some real issues going on here that we wanted to address,” Hanson told the Winona City Council earlier this month.

According to Mn/DOT’s 2017 study, roundabouts reduced the rate of fatal crashes at intersections by 86 percent, cut serious injury accidents by 83 percent, and significantly reduced bicycle and pedestrian accidents, as well. The Mn/DOT proposal for Mankato Avenue would add numerous crosswalks where none exist today, extend a 10-foot-wide bicycle path from Lake Park across Highway 61, and drastically reduce the amount of pavement walkers and cyclists would have to cross to make it safely from the core city to the middle school.

 

City Council vote coming up

Mn/DOT officials plan to ask the City Council early this fall to consent to the agency’s plan to reconstruct Mankato Avenue next year with four roundabouts. So far, the entire council appears on-board. City Council member George Borzyskowski has been an outspoken critic of another major roadway change with promised safety benefits — the Broadway “road diet.” However, after studying Mn/DOT’s Mankato Avenue proposal, he is convinced. “Let the engineers engineer this project out,” Borzyskowski said in an interview this summer. “The state pays them hundreds of thousands of dollars a year. They’re well-educated men and women who design roads and roundabouts and bridges. Let them design this,” he stated.

At a July 6 meeting with Hanson, City Council member Michelle Alexander said that the concerns she hears about the project mostly center around the Highway 61 roundabout. “Some of this is going to be education and just doing it and realizing how it functions,” she said. Borzyskowski added, “The more I hear about the plans and talk about it, the clearer it gets.”

Hanson told the council, “We would not build these if we did feel they were safe or could operate with this volume of traffic.”

Chris@winonapost.com

 

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