Transport operators are facing increasing demands for more efficiency, safety, and better security from the general public as well as from governments. Increasing the use of public transport is also consistent with improving the environment. An important part of the efforts deployed to meet these demands is the ever-increasing use of video surveillance cameras and other sensors throughout their networks (roads, rail, public transport, maritime), to monitor passenger flows, cars flows, and trains to enable staff to be informed of possible congestion, and detect incidents or potential incidents without delay. A major difficulty of this approach, however, is the very large number of sensing devices required to effectively monitor even a comparatively small network. In addition to the cost of the devices themselves, the cost and complexity of the required wiring and maintenance, plus the sheer impossibility of watching everything at the same time, make such a system increasingly ineffective as the number of sensors increases.