  Recently the European Union Agency for Railways (ERA) has received a mandate
for 'the development of common safety methods for assessing the safety level
and the safety performance of railway operators at national and Union level'.
Currently, several methods are under development. It is of interest how a
possible candidate would behave and what would be the advantages and
disadvantages of a particular method. In this paper, we study a version of the
procedure. On the one hand side we analyze it based on the theory of
mathematical statistics. As a result, we present a statistically efficient
method the rate-ratio test based on a quantity that has smaller variance than
the quantity handled by the ERA. Then, we support the theoretical results with
the help of a simple simulation study in order to estimate failure
probabilities of the first and second kinds. We construct such alternative
distributions which the decision procedure cannot distinguish. We will show
that the use of procedures that are optimal in the sense of mathematical
statistics combined with the use of a characteristics that has small spread,
here the number of accidents, is advantageous.
