Source: Derived By NBER By Dividing Traffic Units By Series 08157 (Man-Hours Worked, Railroad Employees). The Seasonal Index For This Data From 1920-1926 Was Derived By Dividing The Seasonal Index For Series 03003 (Revenue Ton-Miles) By Series 08157 (Man-Hours Worked, Railroad Employees).
This NBER data series m03064 appears on the NBER website in Chapter 3 at http://www.nber.org/databases/macrohistory/contents/chapter03.html.
NBER Indicator: m03064
Release: NBER Macrohistory Database
National Bureau of Economic Research, Traffic Units Per Man-Hour Worked By Railway Employees For Whom Hours Are Reported for United States [M03064USM613SNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M03064USM613SNBR/, July 7, 2015.