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 iron 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 , which applied an estimated 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 century-old bridge was destroyed in less than 30 seconds. Aftermath The state decided not to rebuild the Kinzua Bridge, which would have cost an estimated $45 million. Instead, it was proposed that the ruins be used as a visitor attraction to show the forces of nature at work. Kinzua Bridge State Park had attracted 215,000 visitors annually before the bridge collapsed, and was chosen by the Pennsylvania Bureau of Parks for its list of "Twenty Must-See Pennsylvania State Parks". The viaduct and its collapse were featured in the History Channel's Life After People as an example of how corrosion and high winds would eventually lead to the collapse of any steel structure. The bridge was removed from the National Register of Historic Places on July 21, 2004. The Knox and Kane Railroad was forced to suspend operations in October 2004 after a 75 percent decline in the number of passengers, possibly brought about by the collapse of the Kinzua Bridge. The Kovalchick Corporation bought the Knox and Kane's tracks and all other property owned by the railroad, including the locomotives and rolling stock. The Kovalchick Corporation also owns the East Broad Top Railroad and was the company that owned the Kinzua Bridge before selling it to the state in 1963. The company disclosed plans in 2008 to remove the tracks and sell them for scrap. The right-of-way would then be used to establish a rail trail. Sky Walk The state of Pennsylvania reimagined the Kinzua State Park as one anchored by a "sky walk" viewing platform and network of hiking trails. It released $700,000 to design repairs on the remaining towers and plan development of