5) Train Brakes: Heavy haul transportation involves carrying
heavyweight railway freight. The trains have multiple
locomotives, which must coordinate their braking. Song et al.
[115] developed a WSN for brake coordination and monitoring
to reduce the maintenance and inspection requirements. They
attached air pressure sensors to the locomotives and train rear,
installed relay nodes on the carriage roofs, and placed accelerometers
and ultrasonic sensors along the track along with
railway relay nodes.When the front locomotive brakes, the sensors
in it detect the change of air pressure, and the relay node on
the locomotive transmits a message to the other locomotives via
the relay nodes on either the train or the track using a wireless
radio link. The other locomotives can then apply their brakes
according to the message from the lead locomotive. The track
relay nodes are used where transmission via train carriages is
weak such as bends and tunnels. The data regarding the railway
infrastructure from the accelerometers and ultrasonic sensors
along the track can be collected and analyzed for condition
monitoring.