This article proposes a methodology to determine the operational risk, defined as the negative effect resulting from improper operation, of a highly distributed system such as the Railways Overhead Contact Line. This operational risk may be measured by an indicator obtained for each of the sections in which the rail network is divided from information concerning its reliability, status, type, remaining useful life, usage, etc.. With these data and after proper statistical treatment, the indicator will be created in the most objective way, in order to have a tool that helps to the manager to prioritize in the decision ,making optimizing investments in order to raise levels of system availability.