The operation of AVL and RTPI systems is based on various
technical approaches and concepts. Some of these interact
directly with the vehicle location systems and use similar satellite-
based communications networks to calculate vehicle arrival
times. The most common satellite-based type of identifying and
locating a vehicle is a Global Positioning System (GPS). A GPSbased
system is able to determine a vehicle’s longitudinal and
latitudinal location through the calculation of reference data
from at least four GPS satellites. Other technical approaches use
cellular-based communication to determine vehicle location and
from that calculate the vehicle arrival times to upcoming destination
points. The usage of GPS technology in automatic detection
(tracking) of a vehicle has been described in detail by
Mintsis, Basbas, Papaioannou, Taxiltaris, and Tziavos (2003). In
addition, the utility of GSM/GPRS applications in vehicle tracking
is extensively described by Elahi, Malkani, and Fraz (2009) and
Papadoglou and Stipidis (2001). The installation and operation of
such systems, is critical for the provision of reliable and accurate
real time transit information.