Minnesota Bridge Collapse

One Year Later

One year ago, during the evening rush hour in Minneapolis, the I-35W bridge over the Mississippi River collapsed killing 13 and injuring 145. What have we learned and are we any safer today? The terse response is there's been a lot of hot air but little progress.

I am one of the engineers on a forensic team on behalf of victims but I can't tell you much more than what has been reported. Not because I am constrained by lawyers but because the National Transportation Safety Board thwarted all attempts by the victims' engineers to visit the site until all steel and debris was cleared. We do know that the some of the gusset plates (steel plates that fasten two or more beams together) appeared to be too thin (1/2" vs. 1") when installed in 1967. We also know, from photos, that some plates were bent as early as 2003. The bridge was classified "fracture critical" meaning a failure in one beam could cause the entire bridge to collapse. Furthermore, work crews, on the day of the collapse, had piled up more than 550,000 lbs of material in one small area of the bridge.

Imagine a brief case handle attached by two flat metal plates screwed into the case. One of the plates is visibly bent and a bit separated from the main case. You continue to carry this around for four more years and one day fill it with bricks. Would you be surprised when the handle fell off and your briefcase fell to the ground? This is a simplistic analogy but based on what's been put out so far by the NTSB it may be a fair example.

The questions are how could this bridge have been built with steel plates that may have been too thin? Why did inspectors not flag the bent and too thin plates and urge action? What impact did the very heavy loading have? I don't have answers for this bridge in particular but it does raise concern for the health of our bridges nation-wide. In a nutshell, our inspections are insufficient, maintenance is poor, and we are way under budgeted for capital repairs. But this is not an intractable problem. Many European and Asian countries are handling their infrastructure issues satisfactorily.

The country's bridge inspection programs are largely visual and are, pretty much, subjective. Yet instruments exist that can measure subtle, unusual movements in bridges, spot cracks in steel before they are visible (disclosure: I am a shareholder in a company that does this), acoustically "listen" to bridges to identify changes in patterns and much more. Nonetheless, I estimate that 99% of inspections are still visual. These technologies are relatively low-cost and can be mandated by the feds where appropriate (I'd say in about 10-20% of bridges). In fact, engineers in Minnesota had contacted several companies to do such high-tech inspections in 2006, at least 10 months before the collapse, but never hired them. While I can't say what the outcome would have been I can tell you that when I was faced with a worrisome situation in 1987 with the Williamsburg Bridge I ordered the bridge "outfitted" with all the latest in bridge measuring technology.

The simplest and least expensive approach is maintenance. We can extend the "life" of our bridges by decades if we treat them like machines, which they are. They rise, fall and twist with the traffic loads, and expand/contract with temperature changes. The solution, unlike high-tech inspections, is 19th century mop and pail. Clean them regularly, wash off the deicing salts and lubricate the moving parts. An independent engineer's report, verifying an adequate maintenance program by each state, should be submitted before acceptance by the feds for any capital support.

Lastly, we need money because previous generations starved the bridges of adequate funds. As a country we are spending about 2% of our GDP on infrastructure while China is spending 9% and most of the European countries are at 4-5%. After last year's bridge collapse Minnesota Congressman Jim Oberstar floated a 5 cent gas tax. A bi-partisan commission recommended a 40 cent/gallon gas tax increase phased in over five years back in January. Both were DOA. While I support raising the gas tax (our taxes are about a tenth that of many countries in Europe) I concede it's a diminishing pool and a near impossible "sell." Instead, we should proceed on creating the Infrastructure Bank as proposed by Senators Dodd and Hagel and supported by Senator Obama. It would allow for the raising of bonds to rebuild infrastructure backed by user fees. Congress should pass Oberstar's Bridge Inspection bill that would increase frequency of inspections for bridges rated deficient and expand the use of high-tech inspections. Public-Private partnerships to rebuild bridges, with sufficient oversight, should be part of any long range plan.

It's too late for this administration to get anything meaningful done. Furthermore, the current transportation bill runs out in a little more than a year. This must become a debated issue for this presidential election and a major initiative by the new administration come January. Time is not on our side.

Samuel I. Schwartz is president of Sam Schwartz Engineering, PLLC and was New York City Department of Transportation Chief Engineer from 1986-1990.