These two bridges stretching between Biloxi and Ocean Springs, Miss., show in stark contrast the role that engineering design plays in the fate of structures during storms surges. The bridge on US 90, in the foreground, broke apart, while the railroad bridge behind it stood strong. Air trapped between the girders of the US 90 bridge, while it was submerged in seawater, made highway segments buoyant, causing them to pop loose. By contrast, the railway bridge girders and deck remained intact. The researchers say it performed so well because its girders were closely spaced. Credit: Princeton University School of Engineering and Applied Science