Project overview
Knights Brown was appointed by the London Borough of Hounslow to design and construct a new pedestrian footbridge beneath the Grade II-listed Barnes Bridge, reinstating a key missing link in the Thames Path and removing a 500-metre detour that diverted users away from the river. The £3.9 million scheme created a new low-carbon crossing that wraps around the existing railway bridge structure, providing uninterrupted access along one of London’s most important riverside walking routes. It was formally opened to the public in January 2023.
The completed structure is an elegant “half-through” steel truss bridge, supported by reinforced concrete river piers and designed to maximise views along the River Thames while sitting sympathetically beneath the historic railway crossing. The bridge passes directly under the railway deck and through an environmentally sensitive riverside setting, presenting significant engineering, environmental and logistical challenges.
The challenge
Building beneath a listed railway bridge
The project’s most significant challenge was constructing an entirely new pedestrian crossing beneath an operational Grade II-listed railway bridge carrying one of London’s busiest rail routes. Any construction activities needed to protect the historic structure while avoiding disruption to railway operations and passengers. Throughout the works, structural, vibration and crack monitoring was undertaken to safeguard the existing bridge and surrounding assets.
Working within a tidal river environment
The new crossing is located within the fast-moving tidal section of the River Thames. Two of the bridge’s principal support piers were positioned approximately 20 metres offshore beneath the railway arch, requiring marine construction activities to be carefully coordinated around limited tidal working windows. These conditions significantly restricted access and working time, with some operations only possible for approximately four hours at a time.
Delivering large bridge spans in a constrained location
The bridge was fabricated offsite in four separate sections before being transported to site for installation. The most complex element, Span 2, sat directly beneath Barnes Bridge and required millimetre-level positioning accuracy within a narrow tidal installation window. Original proposals involved a dual-crane lift requiring railway possessions, which would have increased cost, disruption and operational risk. Knights Brown therefore needed to develop an alternative installation methodology that eliminated the need for rail closures while maintaining programme certainty and safety.
The solution
Innovative marine construction methodology
To maximise productivity on the tidal foreshore, Knights Brown designed and installed a raised causeway comprising sheet piling and approximately 1,600 tonnes of imported stone. This temporary structure acted as a working platform, crane platform and piling platform, increasing available working windows and enabling the safe construction of the river piers.
The river piers themselves were formed using steel tubular piles up to 27 metres long, driven to depths of approximately 21 metres. Reinforcement cages were installed within the tubes before being filled with a specially designed low-carbon concrete mix. Once cured, precast pier shells were installed and completed to form the permanent support structures.
Precision installation without railway possessions
Rather than lifting the bridge into place from land-based cranes, Knights Brown developed a marine installation solution using a specially adapted floating pontoon and jack-up barge. Extensive planning was undertaken, including:
- Design and construction of bespoke pontoon trestles.
- Sea-fastening, buoyancy and stability calculations.
- Coordination with Tilbury Docks and the Port of London Authority.
- Design of a specialist lifting cradle for Span 2.
- 3D scanning of bridge supports and bridge sections to verify tolerances.
- Installation of locating pins and contingency temporary works to ensure precise bridge placement.
Span 2 was transported along the Thames from Tilbury Docks before being manoeuvred beneath Barnes Bridge on a rising tide. As water levels receded, the bridge section was lowered precisely onto its supports. The installation was completed successfully within approximately 30 minutes, avoiding the need for railway possessions and eliminating disruption to rail services.
Collaborative design and value engineering
Working with COWI, Knights Brown undertook a comprehensive value engineering exercise to improve buildability, reduce material consumption and lower embodied carbon. The bridge’s distinctive diagonal truss members, originally designed as solid steel sections, were redesigned as hollow fabricated sections. This optimisation more than halved the material requirement for these elements while maintaining structural performance and improving constructability.
Further innovations included revising foundation designs, integrating temporary and permanent works where practical, and creating integral deck-to-pier connections that improved resilience to vessel impacts whilst simultaneously reducing foundation material requirements.
Sustainability and carbon reduction
Low-carbon delivery was central to the project from the outset. Engineers used a specialist carbon assessment tool to measure embodied carbon throughout the design development process and assess the impact of value engineering decisions. This enabled the project team to balance cost, buildability and environmental performance at every stage.
The value engineering process delivered significant environmental benefits:
- An estimated reduction of at least 20% in embodied carbon compared with the reference design.
- A further 10% reduction through revised material specifications.
- Total embodied carbon savings estimated between 80 and 120 tonnes CO₂e.
- Reduced environmental impacts during construction through improved foundation solutions and mitigation measures designed to minimise the risk of concrete fines entering the River Thames.
Community engagement
The project team invested heavily in community engagement throughout delivery. Activities included site visits, stakeholder events, “Meet the Contractor” sessions and STEM engagement with local schools. The team also partnered with Thames Tradesmen’s Rowing Club, participating in a fundraising rowing challenge that raised £3,252 for the local Hogarth Community Centre.
The bridge was formally opened with participation from local school pupils, community representatives and London Borough of Hounslow stakeholders, celebrating the creation of a valuable new public asset.
Benefits and outcomes
The Dukes Meadows Footbridge delivers a range of lasting social, environmental and operational benefits:
Improved connectivity
- Reinstates a continuous Thames Path route.
- Removes a 500-metre diversion previously required around Barnes Bridge.
- Improves accessibility and enjoyment for walkers, runners and cyclists.
Reduced environmental impact
- Significant reductions in embodied carbon through value engineering.
- Low-carbon design and construction solutions incorporated throughout delivery.
- Reduced environmental risk to the River Thames ecosystem.
Engineering excellence
- Successful installation of a complex bridge structure in a tidal river environment.
- Millimetre-accurate marine installation completed without railway possessions.
- Zero disruption to approximately two million annual rail passengers using the route.
Quality and stakeholder recognition
- Achieved a maximum Considerate Constructors Scheme score of 45/45.
- Delivered through close collaboration between the client, design team, marine specialists and supply chain partners.
- Created a landmark riverside asset that enhances both the local environment and public realm.
Conclusion
The Dukes Meadows Footbridge demonstrates how innovative engineering, collaborative design and carefully planned construction methodologies can overcome severe site constraints to deliver lasting community benefits. By introducing a pioneering marine installation strategy, reducing embodied carbon through intelligent value engineering and successfully constructing a new crossing beneath a live railway and listed structure, Knights Brown delivered a technically complex project that reconnects the Thames Path while setting a benchmark for sustainable infrastructure delivery.
Commendations
Dukes Meadows Footbridge has been nominated for and won a multitude of awards including a RIBA Regional Award, a Civic Trust Award, the New London Award for Transport and Infrastructure, and was highly commended at the IStructE Structural Awards.
