Automatic vehicle location (AVL or ~locating; telelocating in EU) is a means for automatically determining the geographic location of a vehicle and transmitting the information to a requester.

Most commonly, the location is determined using GPS, and the transmission mechanism is a satellite, terrestrial radio or cellular connection from the vehicle to a radio receiver, satellite or nearby cell tower. Other options for determining actual location, for example in environments where GPS illumination is poor, are dead reckoning, i.e. inertial navigation, or active RFID systems or cooperative RTLS systems. With advantage, combinations of these systems may be applied. In addition, terrestrial radio positioning systems utilizing an LF (Low Frequency) switched packet radio network were also used as an alternative to GPS based systems.

After capture, the tracking data is transmitted using any choice of telemetry or wireless communications systems. GSM and EVDO are the most common services applied, because of the low data rate needed for AVL, and the low cost and near-ubiquitous nature of these public networks. The low bandwidth requirements also allow for satellite technology to receive telemetry data at a moderately higher cost, but across a global coverage area and into very remote locations not covered well by terrestrial radio or public carriers. One system description discloses that locations are polled every thirty seconds.

Applications

From Wikipedia under the GNU Free Documentation License
Tue Aug 11 12:32:13 2009

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Transit management fy 2000 Results Objectives of Transit Management

From Yahoo Image Search: "Automatic vehicle location"
Sun Jul 12 12:29:40 2009