Kinzua Bridge, Mount Jewett, McKean County, Pennsylvania

When the tornado touched down, the winds had increased to at least 94 miles per hour (151 km/h) and were coming from the east, perpendicular to the bridge, which ran north–south. An investigation determined that Towers 10 and 11 had collapsed first, in a westerly direction. Meanwhile, Towers 12 through 14 had actually been picked up off of their foundations, moved slightly to the northwest and set back down intact and upright, held together by only the railroad tracks on the bridge. Next towers four through nine collapsed to the west, twisting clockwise, as the tornado started to move northward. As it moved north, inflow winds came in from the south and caused Towers 12, 13, and 14 to finally collapse towards the north, twisting counterclockwise.
The failures were caused by the badly rusted base bolts holding the bases of the towers to concrete anchor blocks embedded into the ground. An investigation determined that the tornado had a wind speed of at least 94 miles per hour (151 km/h), which applied an estimated 90 short tons-force (800 kN) of lateral force against the bridge. The investigation also hypothesized that the whole structure oscillated laterally four to five times before fatigue started to cause the base bolts to fail. The towers fell intact in sections and suffered damage upon impact with the ground. The tornado took less than 30 seconds to destroy a bridge that had stood for over a century.