In accordance with art. 55 of Directive 2012/34/EU establishing a single European railway area, each Member State must establish a single regulatory authority for the railway sector. In Poland, tasks of this body are carried out by the President of the Office of Rail Transport (UTK). Changes in position and tasks of this authority are associated with implementation of Fourth Railway Package, six legal acts which means a continuation of reforms of rail market in Europe. 4th Railway Package imposes new obligations on regulators, i.e. in matters related to rail traffic management, and planned or unplanned maintenance works on the lines. In the package it is also proposed a new model of cooperation between national regulatory bodies and European Union Railway Agency. National authorities may, among others, ask European Union Railway Agency for an opinion on safety and interoperability aspects. European Union Railway Agency may also carry out a visit into a Member State. In addition, President of UTK is also polish national safety authority and is the competent authority to issue a single safety certificate. In tasks of the national safety authority, President of UTK is also obliged to cooperate with the Agency The purpose of this article is to present new obligations imposed on the Office of Rail Transport in relation to implementation of 4th railway package, in scope of both roles.