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In-Depth Information
tions result from violations of the safety-critical rules that define safe system
performance. The table below illustrates railway accidents in Bulgaria in 10
years period.
Tabl e 1 . A91 - Railway accidents - non-o
cial draft from accidents in Safety Data
Base - for the period of 1998-2009 year, NRIC, BG
Accidents
Number of accidents Number of Fatalities
Collisions
52
5
Derailments
15
Of
persons
caused
by
390
201
rolling stock in motion
At level crossing
61
35
Others
2
9
The data presented includes probable-cause information for each accident.
The main causes for accidents, especially derailments, were reported to be
public behavior and poor maintenance.
2
Modeling Human Behaviour
Human operators are important components of the railway systems, and,
as such, can “fail” if their behavior deviates from the behavior stipulated in
the system specifications. Clearly, human operators are able to avoid and/or
correct incidents or accidents; however, they may also be the cause of such
events. Many methods can be used to analyze the potential deviation from
the rules, but, regardless of the method chosen, the designer must choose the
optimal means of prevention or protection, given the nature of the human
error. Thus, to protect a system from potentially unsafe human behavior is as
important as to protect the entire transportation process from unsafe railway
system behavior.
Human errors are regarded as one of the main causes for railway accidents
these days. In spite of this fact, the consideration of human error probabilities
in quantified risk analysis has been very rudimentary up to now. A lack of
comprehensive data and analysis in literature lead to incomplete estimates
and values.
In general, the human errors could be classified in two categories - errors
of omission and errors of commission [1,6]. The first implies the lost of one
or more steps in a procedure. The last is when a different procedure was
made. The main issue in both of them is that the person is unconscious
of the error. The models of such type of human errors are made using a
well-known techniques predicting human error probabilities and evaluating
