The paper is focused to relationship between rail infrastructure manager and railway undertaking as a subject in railway market. The rail capacity research offers response to questions about possibilities how to satisfy the railway undertaking requirements. The train path allocation is continuous process that is organised by European law in liberalised railway sector. This contribution provides a new look at the issue of rail capacity, its identification and provision for railway transport undertakings. The paper introduces the selected methodologies for railway infrastructure capacity calculation shortly and its importance for non-discriminatory capacity allocation.