@inbook{NBERc3197,
 Crossref = "NBERbarg51-1",
 title = "Appendix C Steam Railroads: How Would a Weighted Ton-Mile Index Behave?",
 author = "Harold Barger",
 BookTitle = "The Transportation Industries, 1889-1946: A Study of Output, Employment, and Productivity",
 Publisher = "NBER",
 pages = "191-214",
 year = "1951",
 URL = "http://www.nber.org/chapters/c3197",
}
@book{NBERbarg51-1,
 title = "The Transportation Industries, 1889-1946: A Study of Output, Employment, and Productivity",
 author = "Harold Barger",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "NBER",
 year = "1951",
 URL = "http://www.nber.org/books/barg51-1",
}