Vehicular Sensor Networks: General Aspects and Implementation Issues - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 227

in conjunction with existing train operations, patterns, and rules. The system is
developed to prevent track authority and speed limit violations and ultimately reduce
the potential for train accidents. It uses wireless communication technology to trans-
mit train movement-related information between locomotives and Network
Operation Center (NOC) computer systems. Information about the train comprises
the track database, speed limits, movement authorities, and work zones loads into
the on-board computer. The system also integrates and interlocks the train informa-
tion with data from a GPS to create, in effect, a safety overlay for train operations.
It considers movement-related information, like the movement authority limits,
speed limits and work zones through both WiFi and radio frequency communication
networks and displays it in a graphic interface inside the locomotive cab. At the same
time, the system pings wayside devices along the track through a low band wireless
communication network checking for broken rails, proper switch alignment, and
signal aspect information. As the train moves, the computer constantly calculates a
warning and braking curve based on all mentioned information. The warning curve
provides a margin of safety to warn the crew so that they can slow or stop the train
before it reaches the braking curve boundary. For example, as the train's warning
curve reaches the limit of the train authority, the train crew receives a warning signal
on the on-board computer to stop. If the locomotive engineer does not stop the train
before the stopping distance is reached, the system will automatically use enforce-
ment braking and stop the train with a full service brake application.
Railway bridge monitoring [ 42 ]. Railway systems consist of huge number of
bridges being used over several decades. It is important to have a system to monitor
the bridge health and report when and where maintenance operations are need. The
railway bridge monitoring systems usually implement battery-operated wireless sen-
sor nodes. The use of wireless transceivers and battery eliminates the need of having
to lay cable to route data or power to the various sensors that are spread on the
bridge. The choice of a battery-operated wireless nodes is key for low-energy con-
sumption so that the maintenance requirements are kept to a minimum. The nodes
need to sleep most of the time to conserve power, but they also need to be ready for
taking accelerometer measurements when there is a passing train. This mechanism
of work is called sleep-wakeup mechanism. On detecting a train, nodes collect vibra-
tion data. The collected data then has to be transferred to a central location, where it
will be used for analyses. The passing trains can be used for the data transfer.

10.7.2 Non-Safety Applications

The non-safety VSN applications do not target safety per se, but allow for construction
of intelligent transportation and traffic management systems. There are numerous
examples in this group ranging from different traffic parameter monitoring (enabling
traffic efficiency), green light optimal speed advisory, automatic door/gate opening,
parking meters, railroad crossing control to unmanned vehicle operation. Some of the
most relevant representatives of the non-safety VSN applications are discussed below.