This brief is the fourth in a series describing commuting in America. This body ofwork, sponsored by American Association of State Highway and Transportation Officials(AASHTO) and carried out in conjunction with a National Cooperative Highway ResearchProgram (NCHRP) project that provided supporting data, builds on three prior Commutingin America documents that were issued over the past three decades. Unlike the priorreports that were single volumes, this effort consists of a series of briefs, each of whichaddresses a critical aspect of commuting in America. These briefs, taken together, comprisea comprehensive summary of American commuting. The briefs are disseminated throughthe AASHTO website (www.transportation.org). Accompanying data tables and an ExecutiveSummary complete the body of information known as Commuting in America 2013(CIA 2013).