Cottage Grove loves its concrete roundabouts. In 2006, it was the first city in the state to build a concrete roundabout. Today, this growing community of just over 35,000 residents located 10 miles southeast of St. Paul is home to five all-concrete roundabouts, with two more planned for 2017.

Project description

In the summer of 2016, the fifth roundabout was built at the intersection of 70th Street (County Highway 22) and Jamaica Avenue, a joint project of the city and Washington County. Like another roundabout constructed this year at 95th and Hadley, the city chose concrete for the project.

“Concrete is in our blood. It’s our standard design (for roundabouts),” said Community Development Director and City Engineer Jennifer Levitt, citing concrete’s durability and performance.

With asphalt, she said, the turning movements of traffic cause rutting and require more maintenance. Washington County Engineer Wayne Sandberg agreed, saying there is less shoving and heaving in concrete roundabouts than those constructed with asphalt.

Unique to the 70th Street and Jamaica Avenue roundabout project was the county’s desire to keep east-west traffic moving during construction, according to Project Engineer Dave Sanocki of Stantec. For this to happen, a bypass lane was constructed on the north side of the intersection. Improvements to 70th Street and Jamaica Avenue, from Indian Boulevard to Military Road, were also part of this project. This included storm improvements and a water main service extension.

The project’s total cost was $3.25 million. Cottage Grove’s portion was about $1.8 million.The county paid about $1.45 million. Approximately $1.7 million was paid with Municipal State Aid, which is funded in part by the state’s gas tax, motor vehicle fees and motor vehicle sales tax. Finally, property owners who benefited from the water and storm sewer extension were accessed $48,000.

The 70th Street and Jamaica Avenue roundabout was designed and constructed to accommodate projected population growth and the expected increase in traffic volume. By changing the markings in the concrete and striping within the roundabout, it can easily be expanded from a 1-by-2 roundabout to a 2-by-2 roundabout, allowing for two lanes of traffic throughout the roundabout. No additional construction or concrete will be needed.

Project Dates

May 2016-October 2016

Project details

• Concrete depth: 7.5 inches with 6 inches of Class 5 Aggregate sub base (100% crushed rock) and 24 inches of select granular borrow (clean sand)

• Total project length: 1.6 miles

• Total Concrete Placed: 4,020 CY for the roundabout, including concrete used for curb and gutter, sidewalks

Team

Owner: City of Cottage Grove and Washington County

Project Lead: City of Cottage Grove (City Engineer Jennifer Levitt)
 Project Designer: Dave Sanocki, Stantec, St. Paul, MN

Prime Contractor: Hardrives, Inc., Rogers, MN

Concrete contractor: Stapf Concrete Construction
Ready Mix Concrete Producer: Dakota Aggregates, Rosemount, MN

Download the case study.