Plymouth points conversions - a cost-effective solution

21 May 2021
Image of railway tracks.
When an incompatibility problem compromised a point machine renewal scheme, Amey devised a cost-effective solution that satisfied the client and enabled the project to proceed.

The Cornwall Life Extensions project for Network Rail included the renewal of 15 point machines at Plymouth with a modern style unit. The existing point machines were obsolete and had become difficult to maintain. Since the line was due to be re-signalled within the next five years, the client specified use of a functionally equivalent design (FED) to keep the renewal costs to a minimum.

The point machine renewals were split between the East End and West End of the layout, roughly 50/50 in terms of units. The East End renewals were delivered as requested using the simplified FED approach. However, on starting the West End design works the Amey team identified a subtlety in the existing circuitry that meant the new point machines were not compatible, necessitating more intrusive alterations to the contactor control relays. Since these alterations fell outside the FED remit, a full design process would be required, increasing costs to the extent the feasibility of the West End points renewal might be called into question.

In response, Amey worked up a revised scope for the renewals which identified a ‘minimal alterations’ approach. The exercise produced a detailed scoping document that individually assessed the renewal requirements on a point end by point end basis. The scoping analysed each individual end and recommended the most appropriate approach while still delivering a safe and maintainable end configuration. The recommendation varied for each point machine, from making the required circuitry alterations in the disconnection box to fully bypassing the existing location with new cabling where this was deemed the most cost-effective solution.

The scoping exercise was instigated and led by the design team but drew on the requirements of the installation and commissioning engineers. It was conducted in close collaboration with the Network Rail project team to ensure the solution was acceptable to the route asset management engineers.

Amey’s flexible, collaborative approach to solving the problem resulted in reduced design and commissioning costs and ensured the renewal of the West End points could go ahead.