Negotiations to buy land to build a four-lane highway leading to the Wisconsin side of a new St. Croix River bridge will begin as soon as April.

About a half dozen landowners — some of them living on farms begun by earlier generations of their families — will be presented with appraisals and purchase offers just months before the Wisconsin Department of Transportation (WisDOT) lets bids for construction. Those bids, in December, will allow road work to begin a year from now.

"It's been the most work in the most compressed amount of time I've ever been involved with," said Dave Solberg, the engineer leading the WisDOT project team.

The three-mile highway project, estimated to cost between $30 and $40 million, is a key piece of the overall $675 million bridge project that will link Oak Park Heights with St. Joseph Township, Wis. Once the new bridge opens in late 2016 or early 2017, the Stillwater Lift Bridge will close to vehicle traffic and become part of a pedestrian and cycling loop trail on both sides of the river.

Some landowners who live in the vicinity of the new highway, which will connect the bridge with Hwy. 64, an existing four-lane highway near Somerset, have said they're unhappy with the plan. One owner, Ed Gillstrom, has said that the highway will splinter farm property and render it unusable.

When the bridge opens, it will bring an estimated 18,000 to 20,000 vehicles on the new highway into Wisconsin, Solberg said Thursday.

The first purchase offers will involve six parcels of land. Prices will be structured on state-arranged appraisals, but landowners who want independent appraisals can do so at WisDOT expense. If no agreement can be reached after that, the agency will proceed with eminent domain, known in Wisconsin as "jurisdictional offer," said Troy Stapelmann, a WisDOT real estate acquisition supervisor.

"It's our last resort. We don't want to do that, we want to come to agreement with the property owners," he said.

Solberg said the highway will be built in two segments. The first will extend about 1 mile from the bridge site to County Road E near Houlton School, where a diamond interchange will be built. The second will run about 2 miles from County Road E north to Hwy. 64.

The first section will be graded, bermed with gravel and used as a construction access road, Solberg said. Lanes will be paved at the same time the new bridge is paved, he said. Two smaller projects allow for a "more robust bidding environment" and allow engineers to better determine soil stability, he said.

"We're trying to identify what we can that will make the bridge [project] more economical to construct," he said.

WisDOT also will construct the Wisconsin portion of the loop trail, which will circle over the Lift Bridge, follow some of the new highway in Wisconsin, cross the new bridge and lead back to downtown Stillwater along the river.

On the Minnesota side, work begins this spring on Hwy. 36 improvements in Oak Park Heights. Initial work will involve reconstruction of frontage roads and removing trees in a neighborhood near the river that was abandoned years ago to make room for new approach roads.

A year ago, Congress approved an exception to U.S. Wild and Scenic Rivers Act, the federal law protecting the St. Croix River. That decision, and President Obama's signature, allowed construction to proceed.