HS2 finishes Westbury viaduct, built with a design it says cuts carbon 39–59%

The 320-metre HS2 Westbury viaduct over a River Great Ouse floodplain near Brackley is complete, and contractor EKFB says it is the first of five double composite viaducts finished.

HS2 Ltd announced the completion on 1 October 2026. Set low in the landscape east of the town, the structure will carry the high-speed line across the floodplain. No other viaduct around Brackley is as long as Westbury, which is among fifteen that EKFB is delivering.

Steel beams between two concrete slabs

The design replaces a conventional all-concrete span, or a steel girder topped by a concrete deck, with a hollow box: steel beams sit between a reinforced concrete slab above and a second one below. HS2 Ltd says this needs less concrete and steel, both carbon-intensive materials, than a traditional viaduct, and that the idea came from recent viaducts on France’s TGV network.

In June 2025 the company put a number on the benefit. It estimated that the double composite approach reduces the carbon footprint of these viaducts by 39% to 59% when compared with spans made from pre-stressed concrete beams lifted into position by crane. It also said the design permits longer spans and shallower beams. The estimate covers the design approach across the group of viaducts rather than a figure measured at Westbury.

EKFB, the joint venture of Eiffage, Kier, Ferrovial Construction and BAM Nuttall that is building the central section of HS2, is using the same structure at Wendover Dean, Small Dean, Lower Thorpe and Turweston.

Westbury is the third-longest of the five and, according to EKFB, the first to be finished. Sources: HS2 Ltd pages on Wendover Dean, Small Dean, Westbury, Lower Thorpe and Turweston.

Double composite viaducts on French high-speed lines

HS2 Ltd’s announcement does not name the French structures behind the idea. A 2013 technical paper by engineers from SNCF’s structures department, Eiffage TP and Eiffage CM describes how the approach was studied for three viaducts on the Bretagne–Pays de la Loire high-speed line: Vicoin (337 metres), La Courbe (374 metres) and Quartier (263 metres). The authors trace the use of a load-bearing lower slab over the piers to the Las Piedras viaduct on Spain’s Córdoba–Málaga high-speed line, built in 2004–2006. Comparing Vicoin with the Landbach viaduct on the second phase of LGV Est, designed without that lower slab carrying load, they estimated the saving in structural steel at about 18%, with similar concrete quantities. Eiffage is one of the four EKFB partners, and Eiffage Metal led the manufacture and installation of the Westbury beams.

How the Westbury viaduct was built

The build ran in stages. First, steel beams weighing 2,695 tonnes on their own were put together on the north abutment and then pushed out over the piers between March and October 2024. To keep friction down during the slide, they ran across temporary steel bearings on low-friction pads, coated in a material HS2 compares to the surface of a non-stick pan.

With the steelwork in place, engineers cast the concrete deck with a travelling formwork, completing one 42-metre section at a time before moving the mould forward. Prefabricated parapets were then lifted onto the edges of the deck and fixed. EKFB credits Eiffage Metal with making and installing the beams, and Infrasolutions Ltd with the specialist deck finishing.

Next steps near Brackley

Some work remains on site. The temporary hardstanding laid under the viaduct to carry heavy plant will be taken up and the landscaping finished, and HS2 Ltd Senior Project Manager Paul Cooper set out the next priority:

“This section of the railway is now really starting to come together, and with the viaduct complete, our focus will turn to completing the earthworks and other nearby structures.”

Nearby, the Turweston green bridge was finished in April and the A43 realignment in July. Across the wider route, HS2 Ltd reports progress on the viaducts over the M42 and M6 near Birmingham and on the approach into Curzon Street station. The project includes more than 500 bridging structures, among them the Colne Valley Viaduct.

HS2 Ltd says the finished railway will speed up travel between London and Birmingham and release capacity on the West Coast Main Line for additional freight and local trains.

The ranges were published by the Department for Transport in May 2026. Source: HS2 Ltd project update.