Short run costs of rail infrastructure do not include just the maintenance costs, but also the operation costs, due to the traffic management activities: management of the switches and time table setting. Though rarely addressed, these costs are not at all negligible; in France for instance, they represent about 35% of pure maintenance costs (i.e. about 25% of the total maintenance+operation costs). This text aims at providing some insights on them and on the associated marginal costs. The approach is primarily an econometric one, based on top-down process where correlation is assessed between operation costs and traffic level at some aggregate level of segments of track; the literature is very poor; indeed we have found no European reference on the subject. We will first present the technical content of this type of expense, second the framework of the econometric analysis, third the results.