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In addition to using in-situ technologies, many network management applications
make use of in-vehicle devices, generically termed Automatic Vehicle Location
(AVL) systems.
AVL devices either provide positional information whenever a suitably equipped
vehicle passes a certain point in the network, or continuous information as the
vehicle travels through a network.
The former system typically relies on appropriate vehicles being equipped with
transponders which transmit and receive information from roadside units.
The latter system uses vehicles equipped with Global Positioning System (GPS)
technology.
The principle of FCD is to collect real-time traffic data by locating the
vehicle via mobile phones or GPS over the entire road network as shown in
Fig. 1.
It represents that all vehicles are equipped with mobile phone or GPS which will
act as a sensor for the road network.
Data such as car location, speed and direction of travel are sent anonymously to
a central processing centre.
After collecting and extracting, useful information such as status of traffic
and alternative routes it can be redistributed to the drivers on the road.
FCD is an alternative or rather complement source of high quality data to
existing technologies.
They will help improve safety, efficiency and reliability of the transportation
system.
They are becoming crucial in the development of ITS.
GPS is becoming more and more useful and inexpensive; few cars had been equipped
with GPS system and were made to pass a certain point in the network.
The vehicle location precision was found to be relatively high, typically less
than 30m.
Generally, traffic data obtained from private vehicles or trucks are more
suitable for motorways and rural areas.
Figure 1:
Communication from GPS, source
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Currently, GPS probe data are widely used as a source of real-time information
by many service providers but it suffers from a limited number of vehicles
equipped and high equipment costs compared to floating cellular data.
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