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You’ve probably heard about the ESC process here and there… but do you really know what it means?

The ESC process was originally introduced because, in the Control‑Command and Signalling (CCS) domain, even a successful certification process cannot always guarantee that an on‑board subsystem and a trackside subsystem will consistently interact as intended under all conditions.

There may be differences in national engineering and operational rules, specification gaps, different interpretations, design issues, or incorrect installation.

For this reason, a quality check may be necessary to demonstrate the technical compatibility of CCS subsystems within the intended area of use for a given vehicle.

These checks demonstrate what we call the ETCS System Compatibility (ESC). 

What is UNIFE/UNISIG opinion on ESC?

Let us clear something up: ESC is a quality check – full stop. Before any ETCS on-board goes live on a real line, proof of that check needs to be in place. 

What ESC is not – and this distinction matters – is a substitute for safety, certification, or authorisation. Its lane is route compatibility, and route compatibility alone.

The problem? Today, that boundary is not being respected. And that is something we need to fix.

While there are positive examples, the ESC process is implemented very differently across countries, creating high costs and limiting the flexible use of rail vehicles. Constant updates to ESC checks and types add significant effort for infrastructure managers, a challenge that will only grow with ETCS Baseline 4 and future system evolutions.

Although a few compatibility issues remain, they are minimal and sometimes linked to unexpected trackside engineering and increasingly less linked to ETCS on-board.

UNIFE/UNISIG supports the EU goal of a Single European Railway Area and is ready to take a more proactive role in ESC checks, including wider access to supplier labs, provided that effort at application level can be reduced.