United States. Government Accountability Office. Freight Railroad Safety: Hours of Service Changes Have Increased Rest Time, but More Can Be Done to Address Fatigue Risks, report, September 28, 2011; (https://digital.library.unt.edu/ark:/67531/metadc298306/m1/1/: accessed September 25, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .