People rarely think about culverts until they are gone. These plain pipes and boxes carry roads over streams and span less than 20 feet—the federal cutoff for what counts as a bridge. That means road-stream crossings stay out of the National Bridge Inventory and therefore, off the inspection schedule. Yet, when Tropical Storm Irene tore through New England in 2011, it destroyed more than 960 of them in Vermont’s Green Mountains alone and left 13 communities entirely cut off for days.
