Technical interoperability is at the core of virtually any reform of the EU railway sector. To create the single European railway area with smooth cross-border train operations, the EU decided to impose harmonisation of technical interfaces and subsystems in the form of technical specifications for Interoperability: Technical Specifications for Interoperability.

The first such Directive was adopted in 1996 with 1996/48/EC, which was amended 5 years later by 2001/16/EC, and again 3 years later by 2004/50/EC. These were amended 4 years later by recast directive 2008/57/EC, which received further amendments in 2009 by 2009/131/EC and 2011 by 2011/18/EU.

⇒ With each Directive, the EU extended the scope of interoperability and strengthened the role of the EU vs the Member States. However, the powers and the status of the ERA remained unchanged.