@inbook{NBERc4612,
 Crossref = "NBERhult48-1",
 title = "Some Needed Composite Measures of Traffic",
 author = "Thor Hultgren",
 BookTitle = "American Transportation in Prosperity and Depression",
 Publisher = "NBER",
 pages = "73-79",
 year = "1948",
 URL = "http://www.nber.org/chapters/c4612",
}
@book{NBERhult48-1,
 title = "American Transportation in Prosperity and Depression",
 author = "Thor Hultgren",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "NBER",
 year = "1948",
 URL = "http://www.nber.org/books/hult48-1",
}