Relearning Lessons Learned
Engineering failures, like the Atlanta highway collapse, inspire real-time class discussions on risk, responsibility, and repeated mistakes.
By Henry Petroski
When an elevated section of Atlanta’s Interstate 85 collapsed during a fire in late March, commuters and highway officials alike anticipated an apocalyptic traffic snarl. Another “carmageddon” was predicted, five years after the name was used during a shutdown of Los Angeles’s I-405 for weekend construction. Just as their counterparts had in California, drivers in Georgia adapted brilliantly, and the dreaded traffic nightmare never materialized.
Shortly after the Atlanta collapse, the Department of Transportation announced that the road, which carries as many as 250,000 vehicles daily, would be out of service for about 10 weeks. In the engineering classroom, this allowed plenty of time for an extended teachable moment. Even if based on media reports rather than official failure assessments, which might not come for many months, tentative analyses of the highway collapse could be worked out on the whiteboard and updated as revised information became available.
And therein might be lesson one: Facts take a while to shake out after a failure. The cause of the fire, for example, was at first muddled, with early reports stating that it involved PVC piping, or rubber tires, or an old couch that a homeless person set aflame. Whatever the cause and the fuel, the fire burned very hot.
Structurally, the affected section of viaduct consisted of a series of bridge spans over a highway department storage area. The mechanics of the failure are not difficult to posit: The flames engulfed the bridge beams, and the intense heat affected the strength of the concrete and the steel threaded through it. The weight of the weakened beams themselves, plus that of the roadway they supported, became too much to bear.
This is not a complicated or exotic scenario, so why was the highway not designed to obviate it? Why weren’t the beams designed to be stronger or more fire resistant? Aren’t engineers expected to think, as part of any design, of all the ways in which a structure can fail? Or can designs, like broths, have too many cooks?
These kinds of questions can turn a classroom of passive note takers into a discussion group of thinkers. As a byproduct, students can become engaged in current events and how they are affected by engineering and other decision making—or the lack thereof.
Should ensuring that a fire cannot start beneath a highway be part of its design? Should the underside of a bridge over a storage area be equipped with fire suppression systems? Where does the structural engineer’s responsibility end? The professional and ethical issues are as numerous as the technical.
The Atlanta collapse can also prompt questions relating to the uniqueness—and therefore the likelihood—of a large fire damaging an elevated highway structure. Has there ever before been such an occurrence? If so, what is their excuse for not having taken the risk into account?
If not, are engineers absolved from not having anticipated its possibility?
Among precursors to the Atlanta “accident”—if that is ever a meaningful word to describe a foreseeable failure—was an incident that occurred on the city’s I-285 in 2001. In that case, a tanker truck overturned as it entered the interstate loop, igniting 1,000 gallons of spilled gasoline. The flames engulfed the overpass, causing enough structural damage to close four lanes for weeks.
Good design is about using engineering judgment to whittle down any list of potential failure scenarios. While judgment itself cannot easily be taught, it can be developed through experience, and that can be hastened through exposure to case studies. An actual case of failure contemporaneous with an engineering course can provide a real-time lesson that almost teaches itself.
Carmageddon did not happen in Atlanta because drivers used common sense to avoid the affected section of I-85. For engineers, common sense means using sound engineering judgment and not having to relearn lessons already learned. We engineering educators can help by teaching those lessons as they are unfolding.
Henry Petroski is the Aleksandar S. Vesic Professor of Civil Engineering and a professor of history at Duke. His most recent book is The Road Taken: The History and Future of America’s Infrastructure.
Image Courtesy of Catherine Petroski