"The security threat posed by the nearly 16 million shipping containers that arrive each year at U.S. ports is a major concern for policymakers.1 That concern is partly motivated by the loss of life and damage to property that could occur from a terrorist attack using incoming containers. Another source of concern is the potential loss to the economy if one or more major U.S. ports were shut down for any length of time. At the request of the Permanent Subcommittee on Investigations of the Senate Committee on Homeland Security and Governmental Affairs, the Congressional Budget Office (CBO) analyzed the national economic costs of disruptions in container traffic, regardless of their cause. This report summarizes the structure and economics of the U.S. port industry and container traffic, estimates the economic cost of various disruptions in that traffic, and discusses how such disruptions might affect the economy."
Congressional Budget Office: http://www.cbo.gov/