It's a numbers game: Eight lanes of pavement over a 2-mile stretch in a Washington County city of 4,700 residents -- and millions of dollars at stake.

Whether a new St. Croix River bridge gets off the ground now hinges on solving a public works riddle in Oak Park Heights, the potential new home of a four-lane bridge that will funnel motorists to and from western Wisconsin.

Even after years of discussion, a giant makeover of Hwy. 36 through Stillwater's smaller neighbor to the south remains in dispute. Rebuilding of that stretch of highway -- long planned as essential to the bridge project -- could mean millions of dollars in new taxes for property owners in Oak Park Heights to move and upgrade water and sewer lines.

"It's the next critical issue we have to work through," said Adam Josephson, east metro manager for the Minnesota Department of Transportation (MnDOT). "It's a large cost to the city. I'm confident we can resolve this."

But skepticism runs deep in Oak Park Heights, even as politicians celebrate the passage of legislation in Congress to allow construction of a new bridge and convert the old Stillwater Lift Bridge into a pedestrian and bicycle trail.

"We're not asking for trails, we're asking for sewer pipes," said Mike Runk, a City Council member in Oak Park Heights who sees a lack of enthusiasm in addressing his city's construction costs. The bridge is a big regional project that could leave Oak Park Heights strapped for cash for years, he said.

In the big picture, MnDOT envisions reducing driver delays and unsafe turns along Hwy. 36, a state highway. Slight hills would be eliminated, frontage roads would be moved back from two major intersections to improve safety and turn lanes would be added. The existing roadway would be torn up and rebuilt.

Significant improvements would occur at the intersection that joins Oakgreen Avenue in Oak Park Heights with Greeley Street in Stillwater. A mile farther east, the Osgood Avenue intersection would be reconfigured as well.

It's not the concept but the details that worry Oak Park Heights officials. They'll have to move or replace city water and sewer lines situated in the state's right of way along Hwy. 36. Or -- in a less costly but riskier scenario -- they could leave them alone while road builders pave over them.

"To me it doesn't make any sense to build a brand new road over 40-year-old pipes, which is what MnDOT wants to do," Runk said.

A cost analysis completed for the city in November shows three scenarios ranging from $1 million to $12 million in cost. In addition, combined costs for long-term maintenance and lost tax revenue could total as much as $6 million more.

Oak Park Heights doesn't qualify for state road aid because its population hasn't reached the required 5,000 residents. Josephson said that federal High Priority Program money would be available to pay 80 percent of the total cost of utility work, which would reduce the city's cost to less than $1 million under the scenario where most utilities are left alone.

Only about 20 to 30 percent of all utilities "need to be disturbed," Josephson said.

But the city sees things much differently. If city leaders choose to move their utilities outside the state right of way to city land to maintain more control over them, the cost could mount to $12 million.

"That's where the huge discrepancy in costs comes," Josephson said.

If Oak Park Heights raised property taxes to pay $12 million for the bridge project, the annual increase on a house valued at $250,000 would be $433, the study said.

On the low end, if the city risked leaving utility lines "as is" between the two major intersections that will be reconfigured, the annual increase to property taxpayers would fall to $28.

Because of MnDOT acquisitions that took 98 properties off the tax rolls, the cost study concluded, the city has lost $1.6 million in revenue since 1994. Most of those houses sat in a forested city neighborhood near the St. Croix River, where the major approach work for the bridge will occur. The city also could lose tax revenue on an additional 53 properties, depending on the need for a utility easement, the study said.

In the latest action, city engineer Chris Long will work with MnDOT engineers in hopes of finding a compromise.

Support is strong among business owners along Hwy. 36 for the bridge project, said Mark Swenson, another City Council member.

"It's a nightmare," he said of highway problems in his city. "People are getting sick of it."

But Les Abrahamson, another council member, said it's time for people who have made a big deal out of closing Stillwater's bridge to now make the new bridge project affordable for Oak Park Heights.

"Our gift to the city shouldn't be a tax bill," he said.

Kevin Giles • 651-925-5037 Twitter: @stribgiles