Every five years a new random sample of trucks is selected for the VIUS survey (U.
Our data source is the VIUS (known before 1997 as the Truck Inventory and Use Survey, or TIUS; U.
The VIUS data for 2002, while available, are not used in the present study because the Census Bureau radically changed the industry and commodity definitions used in the survey, and so the 2002 data are not directly comparable to the earlier data years using our present framework.
We found a minimal level of usage of multiple trailers in the VIUS data set.
This is also why our core productivity analysis only covers the years 1982-1997, even though we make use of the VIUS data set for 1977.