Transport for Wales Cwmcynon Viaduct

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Case study snippet

Amey Consulting’s plan for the electrification of the Core Valley Lines (CVL) in Wales required the installation of overhead line equipment (OLE) at the Grade 2 listed Cwmcynon Viaduct. The task was to design a structure that did not compromise the fabric of the viaduct. The Amey designers collaborated with Amey Rail and the Amey structures team to produce a compliant solution that met the technical demands of the project, satisfied the local council and minimised construction delays.

The challenge

Amey Consulting is designing the systems and infrastructure required for electrification of the ageing Core Valley Lines rail network. The poor condition of many of the assets, such as bridges and viaducts, present a particular challenge for the design and installation of OLE.

Cwmcynon Viaduct in Rhondda Cynon Taf borough is a heritage asset built in 1862. An initial outline design for the OLE at the viaduct involved attaching steelwork to the structure. When approached for planning consent, the council expressed concerns about the effects of drilling into the ageing brickwork.

Faced with a potentially serious delay in obtaining consent, Amey produced a revised design for a structure sited at the side of the viaduct. However, this created new issues, due to the viaduct’s location next to a road and river. Highway closures would have been required for the construction phase, and the river presented a flood risk. The proposal also called for the design and manufacture of bespoke brackets that would have meant a further significant delay.

Our approach

Amey Consulting worked collaboratively with the Amey Civils Examinations Framework Agreement (CEFA) team to devise a new, more viable OLE solution. The designers consulted historic records for the viaduct and conducted calculations that took account of prevailing wind speeds, the curve of the track and the span lengths involved.

The resulting design comprises two twin track cantilever (TTC) structures on either side of the viaduct that support the electrification wires without connection to the viaduct. The solution uses standard equipment, eliminating the need for bespoke steelwork. The length of the span across the tracks was a potential obstacle to compliance, which was surmounted by skewing the structures to achieve a shorter span.

The presence of the road and river, along with other factors such as a buried gas main, meant that the steel pile foundations had to be carefully sited. The designers conducted a site survey in conjunction with Amey Rail’s construction team to identify the best locations, ensuring easy access for plant and personnel.


The new OLE solution removes the uncertainties of drilling into ageing brickwork and satisfies the local council’s concerns. With no need to obtain planning consent or commission bespoke steelwork, up to six months of delays have been avoided.

The judicious siting of the OLE structures reduces the need for highways closures, saving time and money, and is also safer for construction workers.

This approach has been applied to other CVL structures such as Heath Viaduct where increasing the span length has avoided having to fit a bespoke civils structure to the viaduct.


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