Border Security: Barriers Along the U.S. International Border [Updated December 12, 2006] [open pdf - 616KB]
From the Summary: "Congress has been considering expanding the barriers currently deployed along the U.S. international land border. Currently, the United States Border Patrol (USBP) deploys fencing, which aims to impede the illegal entry of individuals, and vehicle barriers, which aim to impede the illegal entry of vehicles (but not individuals) along the border. While the San Diego fence, combined with an increase in agents and other resources in the USBP's San Diego sector, has proven effective in reducing the number of apprehensions made in that sector, there is considerable evidence that the flow of illegal immigration has adapted to this enforcement posture and has shifted to the more remote areas of the Arizona desert. A number of policy issues concerning border barriers generally and fencing specifically may be of interest to Congress, including, but not limited, to their effectiveness, costs versus benefits, location, design, environmental impact, potential diplomatic ramifications, and the costs of acquiring the land needed for construction."
CRS Report for Congress, RL33659