The state’s overhaul of Robert Street in St. Paul will begin this summer with the six-week closure of the historic rainbow-arched bridge over the Mississippi River.

After the Fourth of July, the Robert Street Bridge, used by about 18,000 motorists each day, will close for preventive maintenance.

The cost of the project is not yet known, but Carolyn Adamson, the state’s project manager, said the Minnesota Department of Transportation will gather bids from contractors this month.

The work will remove and replace the seal-coat on the bridge deck, add a thin layer of blacktop and cement and fix internal drainage problems that have eroded concrete on the structure. Despite those problems, state transportation officials said the bridge is safe.

The bridge work is the first step to overhauling Robert Street between Interstate 94 and Annapolis Street.

“It is really one of the poorest roads we have right now,” said Kevin Walker, a spokesman for MnDOT.

MnDOT will work with the West Side Community Organization to learn how future construction projects can meet the needs of the community. Walker said the road could eventually look “totally different,” potentially with a narrower roadway to encourage drivers to slow down.

In about 10 years, Walker said, MnDOT will do more to restore the Art Deco-style Robert Street Bridge, which opened in 1926. The bridge last had major work done in 1989.

While arch bridges are common in the Twin Cities, the Robert Street Bridge is the only one in the area with a rainbow arch design, meaning the arch starts under the bridge and crests above the deck.

The bridge was built to carry streetcars and auto and pedestrian traffic while accommodating river traffic and railroad lines underneath.

It was added to the National Register of Historic Places in 1989.

“[Bridges] really play a prominent part in the visual life of the city,” said Larry Millett, a local architectural historian. “It is one of the more unusual bridges in the Twin Cities because of all the practical elements it had to meet when they built it.”

The bridge will tentatively close on July 10 and reopen by the end of August, though weather could affect the timeline. Detours will likely direct motorists over the Wabasha Street Bridge.

Dylan Anderson (dylan.anderson@startribune.com) is a University of Minnesota student on assignment for the Star Tribune.