Dubuque, Iowa, is one city getting a leg up from the feds as it tries to revitalize its downtown. Photo courtesy SD Dirk via Flickr The word "silos" is most often used to talk about grain or coal, not the federal government. But in the case of transportation and housing -- two sectors that accounted for more than 43 percent of the nation's carbon emissions in 2008 -- Washington's siloed approach of divided, blindered policymaking could put wheat farmers to shame. The Obama administration is starting to break down those barriers between agencies, asking the Department of Transportation (DOT), the …