Series Is Presented Here As Two Variables--(1)--Original Data, 1917-1927 (2)-- Original Data 1926-1939. Data Include Passengers On Subways, Elevated Trains, Street Car, And Buses Operated By Street Car Companies, Their Affiliates, And Companies Formerly In The Street Railway Business. Source: Direct From American Transit Association Files; And "Bus Transportation".
This NBER data series a03012ba appears on the NBER website in Chapter 3 at http://www.nber.org/databases/macrohistory/contents/chapter03.html.
NBER Indicator: a03012ba
Release: NBER Macrohistory Database
National Bureau of Economic Research, Total Revenue Passengers Carried By The Transit Industry for United States [A032BAUSA442NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/A032BAUSA442NNBR/, July 28, 2015.