3AAR. Class I railroad statistics[EB/OL]. (2013-01-10) [2014-11-20]. https://www.aar.org/StatisticsAndPublications/Documents/ AAR-Stats-2013-01-10.pdf.
4AAR. Class I railroad statistics[EB/OL]. (2014-07-15 ) [2014-11-20]. https://www.aar.org/BackgroundPapers/Class I Railroad Statistics.pdf.