The ERTMS/ETCS uses its own language to transmit information over radio or/and balise using variables, packets, messages, and telegrams. To allow flexible application, Packet 44 (P44) was specified in the Technical Specifications of Interoperability (TSI) for applications used outside the ERTMS/ETCS system.


The P44 can be used outside the ETCS application by associating with NID_XUSER, which is the variable that uniquely defines the identity number of a specific user system for which the remainder of P44 is intended. The NID_XUSER and P44 can be used for more than one purpose such as ASDO (Automatic Selective Door Operation ) and Speedo Meter Unit change.


Automatic Selective Door Operation (ASDO)

ASDO is a system that can be deployed with ETCS using Packet 44 to compare the length of the train with the length of the platform, sending a signal to the driver so that only the doors on the platform side are opened.

Automatic Selective Door Operation (ASDO)
Photo Credit: Petards Group

Platform information is transmitted by telegram that contains a set of packets including the P44 for each station platform by the balise group which contains information including but not limited to the side of the doors whether on the left or the right side and the length of the platform. This system is used in different countries like Australia (Transport for New South Wales), New Zealand (KiwiRail), and India (The National Capital Region Transport Corporation),... but they are deployed in different ways.

Automatic Train Operation - UK

In the United Kingdom, the Thameslink core section through Central London between St Pancras and Blackfriars became the first ATO route on the National Rail network in 2018. The Thameslink core represents the first deployment of ATO with the European Train Control System (ETCS), also called ATO over ETCS (AoE). The ATO in this project receives its timetable and regulation instructions via the Packet 44 telegram facility in the ETCS Eurobalise. 

ATO-OB. Credit Govia Thameslink Railway (GTR)

Migration to ETCS

Switzerland has been the early adopter of ETCS to control trains. All rail vehicles in Switzerland are equipped with the so-called ETM (Eurobalise Transmission Module). This enables them to read and process information from the national SIGNUM and ZUB train control systems provided by Eurobalises and Euroloops (in packet 44).

Migration to ETCS. Credit Stefan Sommer

Speedo Meter Unit change

Alstom supported by partners at Network Rail, Grand Central and Angel Trains completed FiC testing and accumulated endurance running to prove the reliability of the Alstom ATLAS 2 ETCS onboard system. The Onboard ETCS system fitted to the Class 180 is the first onboard system tested at RIDC that is compliant with ETCS standard Baseline 3 Release 2 (required standard for ECDP rollout). The onboard system is the first to support Packet 44, which enables operation with GB specifics such as miles per hour.

ETCS-fitted Class 180 Train. Credit Network Rail


23 EUG GDL Balise_Engineering v1.0
Presentation ERTMS / ETCS in Switzerland by Stefan Sommer, Head of Business Unit Train Control Systems, 01.11.2012
Modern Railways, Thameslink putting ETCS to work
Rail Business Daily, Rail Innovation & Development Centre carries out its first ETCS retrofit train tests