Resilient railways


Always on



Metro operators are under huge pressure to improve operational availability. One way they can achieve this is by increasing the level of redundancy in signalling systems.
 
Eliminating single points of failure and creating the right level of redundancy increases the percentage of ‘on-time’ operations on metro networks. Redundancy principles can be applied both to individual subsystems and to communication links. This ensures that operations continue smoothly if primary equipment or communications paths fail.
 
Wi-Fi communication is now commonly applied on urban rail CBTC systems. Thales is using Wi-Fi communications with built-in security to protect against unfriendly interference. Redundant rolling radio coverage further enhances the resilience of metro networks
 
In response to the ever-increasing risk from the external environment, Thales is continuously developing countermeasures. This meets the growing customer need for resilience and increases the mean time between service-affecting failures (MTBSAF), as well as minimising the impact of service-affecting failures, which results in greater levels of operational availability. Some examples:
 

Full radio redundancy
Modern signalling relies on radio communications between the track and train. Maintaining communications is vital: if the radio link is interrupted for any reason, and although operation continues, eventually, trains stop automatically once they’ve reached their limit of safe movement authority.
 
To avoid hold-ups and boost availability, Thales uses a specially-designed secure Wi-Fi solution with overlapping radio coverage. One of the benefits of this solution is that it is resilient against interference from co-located Wi-Fi systems, especially in stations.
 
To reduce the risk of interference still further, Thales can provide secure Wi-Fi with a backup radio communications link for its SelTracTM CBTC signalling system. This offers an extra layer of assurance: if the Wi-Fi link is lost, communication to the train can be maintained using a commercial mobile network such as LTE instead.
 
The benefit for operators is that normal service is maintained, even if the primary radio link is not available. The changeover from Wi-Fi to mobile communications is seamless, instant and secure.
 

Subsystem redundancy
Metro operators increasingly rely on software for key applications, such as train supervision and interlocking. These applications are at the heart of metro operations.
 
To meet the need for constant availability, Thales builds solutions that incorporate high levels of software redundancy. Each application is classically run “hot” on synchronised redundant servers, so it’s possible to switch from one to the other with no impact on system performance if there’s a problem.
 
Thales is continuously enhancing availability as a key requirement of its product policy. This will influence not only the way systems are built, but also the architecture of subsystems and selection of components used in their construction.