Using production thinking to extend life of London flyover by more than 50 years

Client: Transport for London

Date: 2024-present

Costain is working with Transport for London (‘TfL’) to deliver safety critical works as part of the A40 Westway Structures Refurbishment project. The key section of the elevated A40 runs approximately 4.5km through the London boroughs of Kensington and Chelsea, Hammersmith and Fulham, and the City of Westminster. 

In 2025, Costain completed a package of works using production thinking, which combines modern methods of construction with new technologies, to successfully extend the life of the critical section of the east-west London artery. The work is supporting local economic growth and prosperity by minimising disruption to the 96,000 vehicles that use the road each day.

The challenge – replace ageing joints to navigate variable UK weather

The bridge structures that support the carriageway and slip roads along the elevated route were built in the 1960s using reinforced concrete, and needed major maintenance to keep the road network running safely and reliably.

Extensive joint gap monitoring revealed that cantilever expansion joints along the route were expanding and contracting, and risked exceeding a movement range of up to 600mm in response to the UK’s variable weather, presenting a critical risk to the bridge structure.

Costain has overseen targeted interventions to replace the ageing joints on the flyover and slip roads, as well as undertaking concrete repairs, waterproofing the deck, resurfacing the road and various other ancillary works.

The approach – offsite manufacturing and bespoke, temporary bridging cover plates

As part of the joint replacement process, Costain’s supply chain partner COWI created bespoke, temporary bridging cover plates using a design pioneered for the M25.

COWI’s design provides a temporary steel bridging plate over the expansion joint, which can carry traffic but is removable during road closures to allow access. This system enables the expansion joint works, which typically take several weeks, to be undertaken outside of peak times in a series of short closure windows. The solution therefore significantly reduces potential disruption to the road network and mitigates the risk of delays or overruns in the works.

Each cover plate weighs up to 5 tonnes and is typically 4m long and 90mm thick. The system is modular and the width across the carriageway can be adjusted, which meant that the plates could be used along the Westway at different joint locations. The plates offer future efficiency and economic benefits for TfL since the solution can be reused for future asset work.

Costain completed the complex installation of seven expansion joints using production thinking. Credit - Costain

“Costain and its supply chain worked efficiently and innovatively to replace the joints that will ensure the road can continue to run safely and reliably for years to come. This was achieved with the least disruption possible to people using the road and living in the area.”

Charlotte Day Project Manager at TfL

Creating a lighter, flexible and more efficient solution

The design of the comb joints was optimised through close supply chain collaboration and design for manufacture and assembly (DfMA). Offsite manufacture and trial assemblies de-risked the installation process, significantly reducing disruption to the road users and allowing the road to reopen on time every weekend. This included the complex completion of a joint replacement, which ran over the A404 and required live traffic to operate continuously on the carriageway.

“The A40 is one of London’s busiest routes and vital to regional prosperity and economic growth, so we wanted to ensure minimal disruption to residents and road users while maintaining our high standards of safety and predictable, best-in-class delivery.

"Our production thinking approach meant we were able to design and deliver a solution that not only removed a critical risk from the programme, but also extended the lifespan of this section of the A40 by more than 50 years.”

Emma Curran Project Manager at Costain

Costain will deliver additional upgrades in 2026

Costain has now installed eight cantilever expansion joints on the A40 Westway, and this year Costain is due to commence the next package of work on the A40 Westway Structures Refurbishment project, which will see it deliver additional improvements and maintenance upgrades at the Marylebone Flyover and on the A40 Westway.

ENDS

Contact

Andy Denman
[email protected]

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