The National Waterways Foundation (NWF), in cooperation with the Maritime Administration (MARAD), released this study to examine the economic impacts of unscheduled lock outages that highlight economic benefits associated with reliable inland waterways navigation. The study was conducted by the Center for Transportation Research at the University of Tennessee, and the Vanderbilt Engineering Center for Transportation and Operational Resiliency at Vanderbilt University.   It studied four geographically different locks on the inland waterways system:  Markland Locks and Dam (Ohio River near Cincinnati), which opened in 1959; Calcasieu Lock (Gulf Intracoastal Waterway in Louisiana), which opened in 1950; LaGrange Lock and Dam (southern-most of the navigation structures on the Illinois River), which opened in 1939; and Lock and Dam 25 (Mississippi River, north of St. Louis), which opened in 1939.  These four locks support traffic on every segment of the Mississippi River system.