@inbook{NBERc9319,
 Crossref = "NBERhult53-1",
 title = "Traffic and Operations since 1938",
 author = "Thor  Hultgren and William I. Greenwald",
 BookTitle = "Transport and the State of Trade in Britain",
 Publisher = "NBER",
 pages = "81-91",
 year = "1953",
 URL = "http://www.nber.org/chapters/c9319",
}
@book{NBERhult53-1,
 title = "Transport and the State of Trade in Britain",
 author = "Thor  Hultgren and William I. Greenwald",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "NBER",
 year = "1953",
 URL = "http://www.nber.org/books/hult53-1",
}