1. Federal Highway Administration, Highway Statistics 2006 (Washington, DC: U.S. Department of Transportation, 2008), Tables VM-3 and HM-15.
2. Federal Highway Administration, 2006 Status of the Nation's Highways, Bridges, and Transit: Conditions & Performance (Washington, DC: U.S. Department of Transportation, 2007), Chapter 6.
3. According to the Brookings Institution, "the working poor spend 6.1 percent of their income on commuting compared to 3.8 percent for other workers" and the "working poor that commute using their own car spend the most; 8.4 percent." Robert Puentes, A Bridge to Somewhere: Rethinking American Transportation for the 21st Century, Blueprint Policy Series (Washington, DC: Brookings Institution, 2008), p. 34.