The U.S. Department of Transportation announced on Thursday it would maintain the adequacy of backup systems for the Global Positioning System (GPS) used for critical transportation applications. Transportation Secretary Norman Mineta said the agency would launch a plan to include back-up strategies and a continued partnership with the Defense Department to modernize satellite navigation systems used in civil transportation. The announcement follows the department's review of a study assessing the vulnerability of the national transportation infrastructure that relies on GPS. The study noted that GPS is susceptible to unintentional disruption from atmospheric effects, signal blockage from buildings and radio signals. There is also the potential for deliberate disruption. The study concluded that air, rail, road and sea users of GPS technology should be prepared for outages and keep ground-based navigation aids on line as back-up. The Volpe report, Vulnerability Assessment of the Transportation Infrastructure Relying on the Global Positioning System, is available online at www.navcen.uscg.gov.