Editor's note: This story was updated at 12:40 p.m. with an additional map.
Draft plans for a new roundabout at the intersection of State Street and Ellsworth Road in Pittsfield Township. Costco is to the northwest of the intersection.
Courtesy Washtenaw County Road Commission
The $2.3 million project will install a two-lane roundabout 160 feet wide, replacing a signal-controlled intersection.
The congested intersection is a main north-south route, as many motorists use the route to get from points south to Interstate 94 and the city of Ann Arbor.
The road commission estimated that traffic at the intersection would only continue to increase after the June 2012 opening of the Costco store near the intersection.
The Costco also has sparked plans for other development in the corridor, as plans for two new retail buildings on South State Street north of Ellsworth were announced in October.
A new Tim Hortons location also is in progress at the intersection at the site of the former Enzo's Sports Bar.
Included in the cost of the $2.3 million roundabout project is a $470,000 water main replacement project by the city of Ann Arbor, said Mark McCulloch, project engineer for the road commission.
That's higher than the $135,000 to $350,000 Ann Arbor officials initially estimated they would need to pay for the project when they approved the plan in May.
The city will be replacing a 30-inch-wide pipe that runs from south to north in the middle of State Street that carries water from wells at the Ann Arbor Municipal Airport to the city’s Water Treatment Plant.
The road improvement project will be paid for by federal dollars, using a mix of Congestion Mitigation and Air Quality grant from the Federal Highway Administration and Surface Transportation Program-Urban funds.
In December, the road commission awarded Stantec Consulting Michigan Inc. with a $173,684 contract for field inspection services for the project.
The road commission plans to put the construction project out to bid March 1 and begin construction in June.
State Street will remain open to traffic during the construction.
Ellsworth Road will be closed in phases to through traffic, although access to businesses in the area will be maintained, McCulloch said.
The roundabout will be the 10th in Washtenaw County.
A public meeting is planned for 6:30 p.m. Tuesday, Jan. 22 at the Superior Township Hall, which is at 3040 N. Prospect Road, for a proposed roundabout at Geddes and Ridge roads in Superior Township.
View Washtenaw County Road Commission work in a larger map
Amy Biolchini covers Washtenaw County, health and environmental issues for AnnArbor.com. Reach her at (734) 623-2552, amybiolchini@annarbor.com or on Twitter.