TIDGET mayday system for motorists

The development of an effective motorist mayday system for travelers in rural and urban parts of the United States and Canada has been hampered by the lack of an infrastructure to receive and process emergency requests and by the inability of most motorists to precisely define the location of their vehicle. The development of intelligent vehicle-highway systems and an expanded network of computer-switched radio systems will greatly improve the ability of highway agencies, both public and private, to respond to emergency requests. The missing element is still an inexpensive and reliable means of determining the location of vehicles in distress. GPS has been proposed as a potential method of providing location in support of a mayday service. NAVSYS has developed a low cost GPS sensor, the TIDGET, for a GPS mayday service. The TIDGET sensor does not track the GPS signals, but instead captures a brief "snapshot" of raw GPS sampled data. This "snapshot" is transmitted to the emergency dispatch facility where it is processed to compute the location of the motorist. The processing also includes aiding data from a map database to allow the vehicle's location to be determined when fewer than four satellites are in view of the sensor. In large quantities, the TIDGET sensor cost is reduced to less than $50 a unit (not including the communications link). The sophisticated software used to process this message at the dispatch center allows the solution to be derived in many cases when only two GPS satellites are in view. The paper includes a description of the TIDGET mayday system and presents preliminary test results.<>