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Infrastructure  >  Signalling  >  ETCS    

> Lineside signals
> The block systems
> Routes and interlocking
> ERTMS / ETCS concept
The author:
Frédéric de Kemmeter 
Railway signalling systems. I'm a rail observer for over 30 years. How has the railway evolved over the decades? Which futur for railways? That's what I'm analyzing and explaining.

Limits of the current system
Train detection
It is very importance for railway traffic management. Regardless of the technology used, this detection: 
1) confirms the occupancy of a section of track. As the system is nested, this results in protection of the section and a warning for downstream sections;  
2) confirms the presence of a convoy at a given location and provides an overall view of the traffic, and therefore its management, in the signal boxes.  
Problem: the technologies used for this detection are very varied and incompatible. A locomotive valid on a network can cause disturbances on the neighboring network, endangering the whole system.
Speed and braking 
These are the two major criteria for railway operations. You can go fast, but you must also be able to brake on time. However, this depends on many factors, first and foremost the weight of the train and the braking capacities of the vehicles.
The lineside signals 
They have illuminating lamps since the 50s and 60s, but their interpretation depends entirely on the driver's attention. Above 200km/h, the interpretation of a signal becomes difficult in bad weather conditions. Errors are still possible (overtaking signals...)

It is based on each national operation. While the three colours - red/yellow/green - are internationally recognized, the same cannot be said for the appearance of each signal, as some countries using multiple combinations of colours to indicate speed limits or an invitation to brake.

The railway concept "one train in one block" contributes to restricting the capacity of a railway line.
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The consequences of the current system
Major technological progress
They are shown above: this map of Europe provides an eloquent picture of the technological salad represented by each National Signalling System (STM). On the other hand, each national system has only one supplier, which thus has a de facto monopoly on design...and on the prices, perpetuating a very expensive closed circuit, especially for small networks with no real room for negotiation.  
The major consequence is the costly change of locomotive at the borders of each network to avoid disrupting the signalling of the neighboring network. An international train thus knows several locomotives over the entire route. It has been possible to eliminate this problem by using locomotives with several national systems, but their maintenance costs are still high and originally these locomotives were built in small series, making them even more expensive.
Strong evolution. The current collected at the catenary is de facto transformed on board the locomotive and the current motors are all three-phase asynchronous. Their possible disturbances on the signalling could cause costly intervention on the railway network (cabling to upgrade).  
Train driving 
The High Sped Train has shown the value of signalling in the driver's cab. Current technologies allow large flows of ground/train data as well as a monitoring of speed and braking curves on board with great precision. 
Signalling management 
Fibre optics nowadays allows to manage large areas of traffic management as well as to encode thousands of routes.
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