From the Document: "The Bureau of Transportation Statistics (BTS), a part of DOT's [Department of Transportation] Research and Innovative Technology Administration (RITA), presents 'State Transportation Statistics 2010,' a statistical profile of transportation in the 50 states and the District of Columbia. This is the eighth annual edition of the 'State Transportation Statistics,' and a companion document to the 'National Transportation Statistics (NTS),' which is updated quarterly on the BTS website. [...] Included in this 'State Transportation Statistics 2010' report is a brief description of the data sources used and a glossary of terms. Also contained in this publication is a summary table that displays the approximate timing of future data releases and contact information for each state's department of transportation."
U.S. Bureau of Transportation Statistics: http://www.bts.gov/