What's eating the American transportation infrastructure? Corrosion. Even the strongest structures eventually fall victim to natural law, but the process is accelerated by human neglect. When will the next bridge collapse? Absent regular care and maintenance, ''it's not a question of whether – it's a question of when,'' says Richard Grant, a principal with Russell Corrosion Consultants. He pinpoints the crisis that's affecting every metal-based structure in the nation's transportation network, and talks about what we must do address it. It's time to ''shift our mindset from reactive to proactive,'' he says.