(USA TODAY) -- Six years after a Minneapolis bridge collapse that killed 13 people called attention to the state of the nation's bridges, there has been minimal improvement and insufficient funding to repair and replace aging spans.
The collapse Thursday of the Interstate Highway 5 in Washington state shined the spotlight once again on troubled bridges.
In 2012, the Federal Highway Administration said 67,000 - 11% - of the nation's 607,000 bridges were structurally deficient. That means the bridges are not unsafe but must be closely monitored and inspected or repaired.
That percentage is little changed since 2007 when 12% of the nation's bridges were listed as structurally deficient and the I-35 bridge collapsed in Minneapolis.
In the wake of that accident, states closed bridges, reduced weight limits or made immediate repairs. All states inspected bridges designed like the one that fell. Some, including Arizona, Delaware, Louisiana, Maine, Minnesota, New Jersey, New York and Tennessee, conducted broader reviews to identify bridges needing the most work.
And others, such as South Carolina and Wisconsin, installed high-tech sensors that record the deterioration of a bridge, which inspectors can track on the Internet.
But funding repairs and replacements continues to be a problem, especially because bridges are getting older, says Andrew Herrmann, an engineer and past president of the American Society of Civil Engineers.
The average bridge in the USA is 42 years old, Herrmann says.
"As bridges get older, we're going to see more problems," he says. "State departments of transportation are going to make hard decisions about what bridges to maintain, what bridges to replace and what bridges to close. We are going to see more closed bridges."
In a 2013 report on the nation's infrastructure, the group said one out of every nine bridges is structurally deficient, but the spans are vital to motorists, who take 210 million trips daily across a deficient bridge.
The group gave the nation a C+ in its report card for maintaining bridges, saying federal, state and local governments need to increase bridge investment by $8 billion annually to meet the needs of deficient bridges.
Washington state was given a C for the overall state of its infrastructure and a C- when it came to its bridges. The group said more than a quarter of the state's 7,840 bridges are considered structurally deficient or functionally obsolete.
The collapse of the I-5 bridge over the Skagit River was triggered by a truck with an excessively tall load that struck a steel girder. Two vehicles fell into the icy water 50-feet below, Washington State Patrol Chief John Batiste said Friday. Three people were hospitalized but there were no fatalities.
The 1,111-foot steel-and-concrete bridge, built in 1955, is listed by the National Bridge Inventory as "fracture critical," which means that the entire structure can be brought down if even one major part fails, the Seattle Times reported.
Bridges that have redundant features are designed to remain intact if a single section is damaged.
The bridge was not classified as structurally deficient, but a Federal Highway Administration database listed it as being "functionally obsolete" - a category for bridges whose design is outdated, such as having narrow shoulders and low clearance underneath.
The bridge, which was inspected last August and November, had a sufficiency rating of 47 out of 100 at its November 2012 inspection, state Transportation Department spokesman Noel Brady said Friday.
The state average is 80, according to an Associated Press analysis.
The 180-foot-wide bridge has two lanes in each direction, Brady said. There are four spans, or sections, over the water supported by piers. The span on the north side is the one that collapsed. It's a steel truss bridge, meaning it has a boxy steel frame.
Maria Feng, a civil engineering professor at Columbia University, said, "It's time we rethink the way we manage our massive infrastructure assets."
She researches new tools and technology to care for aging infrastructure. She says there's obviously a need for more funding, but she says it's not very realistic to expect more.
So she says governments need to do a better job spending the money they do get to care for the structures. She says detailed inspections and analysis of the nation's bridges, based on their use and condition, can help governments prioritize which get fixed first.
"We need to make this a national priority," she says of tackling the problem of aging bridges, roadways and waterways.
Contributing: Associated Press