Colne Valley Viaduct

The Colne Valley Viaduct stretches for more than 3.4km (2 miles) across a series of lakes and waterways between Hillingdon and the M25 on the northwest outskirts of London. It is the longest railway bridge in the UK and almost a kilometre longer than the Forth Bridge in Scotland.

The Colne Valley is an area of diverse countryside with areas of parks, green spaces, and reservoirs. Along with the River Colne and the Grand Union Canal, the valley is a well-used public space offering recreational opportunities for visitors to enjoy.

Viaduct construction

Building work on the viaduct’s deck began in May 2022. Over the following 28 months a dedicated team of highly skilled engineers used a massive bridge-building machine to lower into place the bridge’s 1,000 uniquely shaped deck segments.

The deck segments were made on-site at a purpose-built factory. Each of the segments are uniquely shaped to enable the structure to curve as its 54 arches span up to 80m to carry the high-speed line up to 10 metres above land and water across the Colne Valley.

Once the main civil engineering phase of construction ends the rail systems installation phase will begin. The factory and surrounding buildings will also be removed and the whole area between the viaduct and HS2’s 10-mile tunnel beneath the Chiltern Hills will be transformed into an area of chalk grassland and woodland as part of HS2’s ‘Green Corridor’ project.

Viaduct design

The design of the Colne Valley Viaduct was inspired by the flight of a stone skipping across the water with a series of elegant spans, some up to 80m long, carrying the railway around 10m above the surface of the lakes, River Colne and Grand Union Canal.

Set low into the landscape, wider spans will carry the viaduct crosses the lakes, with narrower spans for the approaches. This design was chosen to enable views across the landscape, minimise the viaduct’s footprint on the lakes, and help complement views across the natural surroundings.

Key facts

• Length: 3.4km (2miles)
• Height: 10m
• Number of piers: 56
• Construction approach: On-site manufacture – deck segments manufactured on-site at a purpose-built pre-cast factory.