It's not yet fully funded and much of it is still on the drawing board, but the Interchange multivehicle transit hub slated for the Target Field area in downtown Minneapolis is about to enter a final planning phase before construction begins early next year.

This week, Interchange manager Ed Hunter will update the Hennepin County Board on plans for the $70 million project. Making the rounds among officials is a draft of the project's environmental assessment, which holds the key to federal funding.

Public meetings will be held this fall to test the right look and feel for the plaza space, which would be the project's public face. The county will tear down its Environmental Services Building to make room for the plaza, and bids will be solicited for design work.

"We have this tabletop that all these functions are going to take place on, but we haven't designed the place settings or the centerpiece yet," Hunter said.

He said he hopes the transit hub will be finished and ready for operations by spring of 2014, in time for the baseball season at Target Field and the Central Corridor light-rail line now under construction in St. Paul and Minneapolis.

Hunter said construction is sure to be disruptive during the next two Twins seasons. Even so, he said, "Everybody gets why it's so essentially important. You've seen the crowds at the ballpark and the success of light rail. When Central comes in, it's only going to get crazier."

The Interchange will consist of the pedestrian plaza, elevated light-rail tracks and underground parking with 550 spaces on the north side of Target Field, close to the current station.

The 1 1/2-acre plaza would accommodate more than 20,000 riders coming and going once the Central line opens.

"This thing is starting to gain momentum and it needs to, because it has a critical timeline here," said Hennepin County Commissioner Peter McLaughlin, chair of the county's rail authority. "We're still on the path to doing that."

The most important next step is filling out funding for the project. To do that, officials are counting on federal dollars.

Cost: Less than $70 million

The project's estimated cost has come down, from $86 million to just less than $70 million. That's partly because construction costs are flat and the project's scope has been pared back somewhat, Hunter said.

The Metropolitan Council this week is expected to allocate $11 million for the project, out of a $20 million bonding package awarded by the Legislature this year to metro transit projects.

Hennepin County's rail authority has awarded $6.7 million for design and start-up purposes. The Minnesota Ballpark Authority -- Target Field's owner-operator -- has committed $1.7 million, including $200,000 a couple of weeks ago to develop the project's look.

Once federal officials sign off on the project's environmental assessment, the project will apply for federal funds. One possible source: the U.S. Department of Transportation's TIGER III program for innovative and multimodal projects, which awarded $35 million last year to the Union Depot project in St. Paul.

"We definitely want to hit the ground running in the spring with construction, so we have two full construction seasons out there," Hunter said.

McLaughlin said he was feeling positive about the Interchange's progress. "I don't see any major stumbling blocks. This project is hard to put together, but it's not as hard as a light-rail line," he said.

Kevin Duchschere • 612-673-4455