The series comes from the 'Current Employment Statistics (Establishment Survey)'
The source code is: CES4348800001
Source: US. Bureau of Labor Statistics
Release: Employment Situation
US. Bureau of Labor Statistics, All Employees: Transportation and Warehousing: Support Activities For Transportation [CES4348800001], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/CES4348800001/, July 31, 2015.