Source: U.S. Bureau of Transportation Statistics  

Release: Transportation Services Index and Seasonally-Adjusted Transportation Data  

Units:  Containers and Trailers, Seasonally Adjusted

Frequency:  Monthly

Monthly rail carloads and intermodals are estimated by dividing the weekly sum by 7 (7 days in a week) and then summing for the number of days in the month (31 days for May, 30 days for June, etc.).

This data is collected by the U.S. Department of Transportation, Bureau of Transportation Statistics (BTS) calculation from data collected by Association of American Railroads.