Traffic will be restricted starting next week on the Kellogg Boulevard-3rd Street bridge linking downtown St. Paul with Dayton's Bluff, following a determination by engineers that the cantilevered piers on the 32-year-old span need to be repaired.

A consultant hired by the Minnesota Department of Transportation (MnDOT) to inspect the bridge last month found that the outer edges of the four-lane bridge aren't properly designed, under existing federal code, to support the heavy daily traffic that the bridge bears.

The pier caps on which the beams sit are cracking, said City Engineer John Maczko.

"It isn't that the bridge is in danger of falling, but the information that we have now, that we are seeing deterioration in the piers, means that we are always going to err on the side of safety," Maczko said. "One can think back not too far to the 35W bridge, and that's nothing that we want to happen."

Technically, the bridge is deemed "structurally deficient" — which doesn't mean it's unsafe, but that it needs significant maintenance, rehabilitation or replacement.

The latter option appeared to be the favorite of Mayor Chris Coleman and City Council President Kathy Lantry, who said Tuesday that they will seek state and federal money to rebuild the bridge.

"We are working in collaboration with our county, state and federal partners to identify funding sources to build a new bridge as soon as possible," Lantry said in a statement.

Maczko estimated it might cost $8 million to repair the bridge, which is 1,914 feet long — a little more than a third of a mile — and rises above Interstate 94, train tracks and the Bruce Vento Nature Sanctuary.

He couldn't say how much a new bridge would cost. About 10,300 vehicles use the bridge daily.

"We're basically looking at the option of spending millions to rehab it, or spending a few million more to get something that meets today's needs," he said. "That's the evaluation that's taking place."

Other considerations in deciding on repairing vs. rebuilding: possible transit use, better cycling and pedestrian lanes, and streetscape improvements such as historic-style lanterns and ornamental iron railings that the Dayton's Bluff Community Council has been lobbying for since 2006.

Lane closures start Monday

One in nine bridges in the United States was considered structurally deficient in 2013, according to a report by the coalition Transportation for America. Minnesota was ranked 32nd — meaning that 30 states and the District of Columbia scored worse — with 9.1 percent of its bridges judged structurally deficient. But the average age of those bridges is 67 years, far older than the Kellogg bridge.

Coleman said that the city is "acting swiftly in the interest of public safety … despite the fact that the bridge has functioned for more than 30 years and the obvious challenges this will pose to movement in the city."

The city will close the bridge to traffic at 9 a.m. Friday for previously scheduled work on nearby Prince Street, giving engineers the chance to restripe the bridge and equip it with signs and traffic devices over the weekend.

The bridge will reopen at 6 a.m. Monday in time for rush hour, but with traffic lanes restricted to three lanes in the middle of the bridge deck. Alternative routes include Interstate 94 and 7th Street. A path will be provided for pedestrians and cyclists.

The bridge was built by MnDOT in 1982 and a year later turned over to the city, which has maintained it since.

Maczko said the city has performed annual inspections in accord with federal standards and has been monitoring the bridge more closely since 1995, when cracks were first discovered in the cantilevers. Funding was budgeted this year to address signs of stress in the pier caps, he said.

"The inspection system has done exactly what it was supposed to do," he said. "It allowed us to catch this and plan appropriately before disaster would happen."