ST. PAUL — Two bridges that, for now, span the Mississippi River side by side are more than just old and new crossings of the heavily traveled Highway 61 in Hastings. They are symbols of an aggressive push in Minnesota to deal with deteriorating bridges after an eye-opening tragedy.

The skinnier steel truss bridge — long identified as a worrisome structure — is being demolished a section at a time now that two lanes of a state-of-the-art concrete bridge carry the load. By winter, all four lanes will be open.

As these projects go, the swap happened in a flash once state transportation officials determined the old bridge had been pushed to its limit. It was originally scheduled to be replaced starting in 2018. The project moved ahead with haste following the collapse of the Interstate 35W bridge in Minneapolis.

The city’s residents had grown leery of the rusting bridge and are ecstatic about its $130 million replacement, said Mayor Paul Hicks. “They’re proud of how it looks and that it is new and that they don’t have to worry about traveling over a rickety old bridge,” he said.

Bridge safety remains a topic of concern nationwide as aging structures take on serious signs of wear. A new Associated Press analysis of federally collected data shows that thousands of bridges coast-to-coast have multiple red flags.

More than most places, Minnesota has a heightened vigilance around bridge conditions since the I-35W bridge buckled during an August 2007 rush hour — a disaster that killed 13 people. In response, lawmakers raised the state’s gas tax to finance a 10-year bridge construction program focused on tackling those with deep-seated problems. Some $1.2 billion has gone into the effort so far, according to the Minnesota Department of Transportation.

The campaign has helped to roughly cut in half the starting-point list of 172 state bridges deemed structurally deficient, fracture critical or both. Among the remaining bridges, 27 were determined to need only routine maintenance in the near term. A few others have private owners.

A bridge is typically labeled “structurally deficient” if regular inspections uncover significant deterioration such as advanced cracking in concrete or steel components. The rating often leads to weight restrictions and increased monitoring and maintenance. “Fracture critical” is applied to bridges without multiple backup features, meaning that if one critical component failed, the entire structure could give way.

In the years since the I-35W collapse, dozens of Minnesota bridges, including some managed by local governments, have undergone significant rehabilitation or outright replacement. Many were simply closed. Still more will be fixed or torn down before the current campaign ends. Some, like the Hastings bridge, leaped years ahead on the construction schedule. Along the Mississippi River alone, six Minnesota bridges will have been rehabbed or replaced by 2018.

Nationally, the AP’s analysis identified 7,795 bridges that are both fracture critical and structurally deficient. The tally relies on data that states submitted a year or more ago for the federal government’s National Bridge Inventory.

After factoring out bridges that were since closed, fixed or replaced, Minnesota’s count of bridges with both designations stood at 33. They range from the Highway 1 bridge over the Red River in far northwestern Minnesota to the Highway 43 span over the Mississippi River in Winona. Many are township bridges crossing small creeks.

The number is hardly static; as some bridges get reworked, others gain the structurally deficient label as inspectors come across new faults. There is also a lag in updating the data in the federal clearinghouse. Two bridges were added to Minnesota’s list after inspections in 2011 and 2012 found deficiencies, officials said.

MnDOT’s State Bridge Engineer Nancy Daubenberger said without the significant infusion of money, it would have been hard to make so much progress so fast. Some of the bridges required tens of millions of dollars in work — what those in the field regard as “budget busters.” And getting the number of bridges that are structurally deficient and fracture critical down to zero might not be practical, she said.

“Will there be a day where we have no fracture critical bridges in the system? Quite possibly,” Daubenberger said. “But at this time we recognize that we need to preserve some of these old bridges that might be fracture critical because of their historic nature.”

The extra money devoted to Minnesota bridge work is due to run out in about five years. Minnesota lawmakers tried but failed to advance a major transportation financing plan last session, but plan to try again in 2014.

Senate Transportation and Public Safety Committee Chairman Scott Dibble said it’s imperative that he and his colleagues avoid a funding lapse that could stall progress. He thinks the 35W bridge tragedy will continue to keep the pressure on.

“I don’t think the collapse is ever going to be too far from minds,” the Minneapolis Democrat said. “That was very, very defining. We will have a long-lasting connection to that.”