Inspired by aircraft control systems, researchers from the University of Birmingham have developed a new cutting-edge ‘fault tolerant’ railway switch (points) technology that they say will continue to work when two out of three of its actuators fail.
While conventional railway switches guide trains from one track to another by sliding a pair of tapering rails horizontally, the new design, dubbed Repoint, uses a lift-and-move mechanism that includes a passive lock for when the points are in place. This is combined with a stub-switch type layout, which offers advantages in many situations. Importantly, the switch is fault tolerant, continuing to work even when two of the three actuators, which control the movement of the points, have failed.
The team developed a digital twin (dynamic simulation model) that it then used to show that the design meets and exceeds requirements for speed and performance. The researchers investigated the performance of the switch using a novel method for simulating track system behaviour, which combines rail bending with physics-based models of actuators and control systems. The simulation scenarios included one of power failure to four of the six motors that drive the actuators and showed that a single actuator is capable of lifting and moving the points to the desired position.
Repoint was developed by Professor Roger Dixon, who led a team at Loughborough University until 2018, and is now professor of control systems engineering at the Birmingham Centre for Railway Research and Education.
The research was inspired by a joint call from the Engineering and Physics Research Council and the UK Rail Safety and Standards Board to look at ways of improving capacity on existing lines. It was clear that railway track switching was a significant limiting factor to growing capacity, and so a project to re-imagine the switch was proposed and subsequently funded.
‘Although switches account for less than five per cent of railway track miles, they contribute to 18 per cent of delay minutes, and 17.5 per cent of delay costs in the UK,’ Dixon said.
The team engaged with operators, maintainers and designers to understand the limits and issues with existing switch technology, which has been in use for more than 200 years. One of the most significant findings was the ‘single point of failure’ that’s embedded in traditional switches and their detection systems, which is why the new switch incorporates a fault-tolerant design.
According to the researchers, Repoint actuation is at technology readiness level 4–5. It has been successfully tested at a test track, which demonstrated its compatibility and functionality with conventional switch rail arrangements. The researchers are now seeking partners and funding to design and fully test the full Repoint system, including the actuators, p-way and interfaces to signalling.
The research has been published in Railway Engineering Science.