on the track. Monitoring the forces exerted using strain sensors
can identify defective axles and wheels [118] or incorrectly
loaded trains [41]. Analyzing the track vibration data produced
by accelerometers [16] and the AE signal transferred through
the rail [7], [22], [121] from AE sensors can also detect out
of round wheels as trains pass. Belotti et al. [16] incorporated
an inductive axle-counter block into their system for assessing
the train speed. The speed affects the expected vibrations; thus,
the speed can be built into the wheel analysis model. Detecting
wheel faults can also pinpoint trains that are at risk of causing a
derailment. In [10], [71], the risk of derailment is represented by
the ratio between the lateral and the vertical force (L/V ratio),
which quantifies the relationship between the applied load and
the deflection of the track [10].
Condition monitoring protects both the trains and the track,
increases the track and train reliability and allows repair to
be scheduled. If the track has been marked as defective and
awaiting repair but is still usable, AE sensors can be attached to
monitor the defects and ensure that they are not getting worse
[135]. Track awaiting repair usually has a speed restriction
enforced so, if it is monitored, this may not be required.