Automatic vehicle location (AVL) systems use GPS and other technologies to track vehicles in real-time and relay their location, status, heading and speed to a control center. AVL uses satellite navigation systems like GPS as well as land-based communication methods. There are two main types of tracking systems - passive tracking uses GPS to store location data for later retrieval, while real-time tracking combines GPS and cellular networks to transmit vehicle position continuously. AVL provides benefits like monitoring vehicle location, arrival/departure times, and driving behaviors, and has applications in fields like military logistics, delivery services, and fleet management.