208 PART | V The future of ITS applications
piezoelectric sensors, magnetic loops). The sensor detects vehicles using pres-
sure or magnetic effects and transfers this information to the data recorder on
the roadside. The main problems with such devices are their short life as they
are affected by the passing of heavy vehicles and the high cost of application and
maintenance. Noninvasive on-site techniques employ local range, but remote,
observations. Human observers have been replaced by machines that employ
technologies such as infrared, magnetic fields, microwave or acoustic radars, or
video cameras. The latter is the most popular on-site nonintrusive technique, in
which the road section under consideration is systematically recorded and then
analyzed with special image recognition algorithms, that output the traffic load,
speed and traffic composition from video streams (Fig. 19.2). On-site observa-
tion technologies have lower cost and longer life than invasive technologies,
but require advanced processing capabilities in the collection step and faster
network connection when data processing takes place in a remote location.
FIGURE 19.1 The structure of an ITS from the data perspective.