The tanker truck full of gasoline lost control and burst into flames on a California highway exit ramp, blasting the bridge above it with intense heat. The bridge was supported by girders made of steel — the reliable workhorse material of modern infrastructure, used to support skyscrapers and bridges the world over. Yet it lasted all of 17 minutes. That fire, in Oakland, Calif. in April 2007, was eerily similar to what happened in Northeast Philadelphia on Sunday morning, when a tanker fire brought down an overpass on Interstate 95. Investigators have just begun to analyze what caused the 105-...