The United States' net public investment in infrastructure dropped by more than 50 percent between 1968 and 2005, according to a report from the Washington-based Economic Policy Institute (EPI). EPI's Global Policy Network Coordinator Tony Avirgan, motivated by the collapse of the Interstate 35W bridge in Minneapolis in July, studied infrastructure spending nationwide. According to Avirgan's study, infrastructure spending took up 2.2 percent of the U.S. gross domestic product in 1968, a time when the nation's interstates were being built, but dropped to 1 percent in 2005.

Avirgan cites the political difficulty of raising taxes to finance further infrastructure spending as the reason for the decline. Avirgan's study is an “Economic Snapshot” on EPI's Web site, www.epi.org.