In 2001, a Volpe Center study assessed the vulnerability of the transportation system to loss of the Global Positioning System (GPS).1 Subsequent to this assessment, the Secretary of the U.S. Department of Transportation initiated an examination of approaches to mitigating this vulnerability. One system-wide possibility is to modify plans for the existing LORAN system, which is currently scheduled to cease operations in 20082, to serve as a back-up to GPS. Within the U.S. Department of Transportation, there is a concurrent activity to provide a technical assessment of LORAN's capability to provide this mitigation.