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Railway Localization

Introduction

Despite high braking distances and track guiding the railway is one of the safest means of transport. There are only 2.7 injuries and 0.04 deaths per one billion passenger kilometers. On the opposite there are 275.8 injured and 2.93 deaths in passenger cars [Statistisches Bundesamt, Unfallstatistik – Verkehrs­mittel im Risiko­vergleich, 2010-12-01]. This safety is due to the extensive control and safety systems in the rail sector, which ensure that no dangerous movements can take place.

In road traffic the driver always drives on sight, which means that regardless of the signal stated by a traffic light, he can respond to obstacles in front of him. In contrast the railway runs strictly signal based. The driver always trusts in the correctness of the given signal and obeys it.
The distance between two signals is called block section. A train may enter the next block section only if it has been surely declared to be vacant. This procedure is called drive in fixed spatial distance. The utilization of a track is thus dependent on the length of each block section. The shorter the block sections are the better the utilization will be, however the signaling and control effort increases as well.

To ensure an efficient railway operation in the future it is important to optimize the utilization of the rail network. In this context a safe railway localization is becoming more and more important.

Research

It is investigated by what means a safe localization can be realized.

Amongst other things, a safe localization is of interest by the following reasons:

  • As driving in absolute braking distance gets possible, existing lines can be utilized better.
  • The existing signaling equipment on the track can be made unnecessary which means huge cost savings.
  • It is the basis for further applications such as automated train operations.
  • More accurate information for the driver or passengers can be provided.

The research is part of the innovation alliance between the Deutsche Bahn AG and the TU Darmstadt within the AG Signalling.

Challenge

At a first glance the localization of a train may seem simple, considering that nowadays every owner of a smartphone can almost everywhere track down his position up to a few centimeters within seconds. Why should that not be possible for trains as well?

Here the problem is less the technological realization of an accurate localization system. The difficulty is to develop a system which demonstrably meets the simultaneously high requirements of accuracy, availability and reliability necessary to ensure safe railway operations.

Modern train control systems such as Linienförmige Zugbeeinflussung (LZB) or the European Train Control System (ETCS) already allow a safe and more accurate localization compared to a block section based precision. However these systems are very complex in installation and maintenance, so they are only worthwhile for busy routes.

Therefore the challenge is to ensure a safe localization under all circumstances and to keep the implementation complexity of the localization system as low as possible at the same time.

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