Councillors in Hammersmith and Fulham have formally backed a transformative plan to replace the ageing Hammersmith flyover with an underground tunnel, a move designed not only to free up valuable land for development but also to enhance traffic flow and reduce the mounting maintenance challenges posed by the existing structure. Originally constructed in the 1960s, the flyover extends 622 metres and serves as a vital artery linking central London with Heathrow Airport and the western parts of the capital. However, inspections as far back as 2011 revealed serious corrosion issues that led to an emergency closure before the landmark 2012 Olympics, prompting a complex £100 million reinforcement project supervised by engineering firm Ramboll.

The latest council report highlights concerns about the long-term viability of the elevated road, citing escalating costs for upkeep and increasing risks of structural failure. The proposed tunnel, now supported by local residents, the Mayor of London, and Transport for London, could be financed in part by the value of residential and commercial developments made possible by reclaiming the land after the flyover’s removal. This land, the council suggests, offers an opportunity to create sustainable communities with new affordable homes and office spaces, alongside green areas that would reconnect Hammersmith with the River Thames, currently divided by the imposing flyover. Additionally, tunnelling the A4 could address chronic congestion at the Hammersmith Gyratory system, notorious for long queues and bottlenecks during disruptions.

This visionary plan is part of a draft local development strategy slated for public consultation, carrying ambitious environmental benefits. By moving roads underground, the council aims to significantly lower pollution levels and introduce green spaces planted with thousands of trees, which would naturally filter toxins and reduce urban heat by up to 40% during heatwaves. The initiative has historical precedent; Boris Johnson, while Mayor of London a decade ago, identified the potential for such a tunnel as part of the area's regeneration.

This concept, known as the "flyunder," is not new. The Borough first proposed the tunnel in 2014 with detailed feasibility studies presenting three main construction options, ranging from a 15-metre deep cut-and-cover tunnel priced at £218 million to extensive twin-bore tunnels costing upwards of £1.7 billion. At that time, the council anticipated that land released from demolishing the flyover could generate up to £1 billion through development deals. The project received backing from Transport for London and then-Mayor Boris Johnson, who described it as a "brilliant" idea, though its progression was linked closely to securing funding conditioned on the land’s development potential.

The Hammersmith flyunder proposal aligns with broader trends in London’s significant tunnelling and infrastructure upgrades, highlighting the capital’s ongoing efforts to modernise and ease urban pressures. Recent large-scale tunnel projects such as High Speed 2’s Northolt tunnel, which completed its excavation phase in mid-2025, showcase the city’s advanced tunnelling capabilities. This HS2 project, employing sophisticated tunnel-boring machines through challenging geology, reflects the technical proficiency available for ambitious undertakings such as the Hammersmith flyunder.

Additionally, Transport for London has experience managing major river crossings underscored by the Silvertown Tunnel project—a £1 billion twin-bore tunnel under the Thames, awarded to the Riverlinx consortium and expected operational by 2025 after delays. Similarly, Highways England’s Lower Thames Crossing, a £6.8 billion to £8.2 billion project involving 23 kilometres of new road including twin 4.2-kilometre tunnels, reflects the scale and complexity of modern river tunnel projects supporting London’s transport network.

London's infrastructural evolution is further supported by ongoing ground engineering frameworks initiated by TfL to bolster geotechnical design and investigations across the capital, facilitating a range of urban development projects.

Thus, replacing the Hammersmith flyover with a tunnel not only addresses immediate concerns about ageing infrastructure and traffic congestion but also forms part of a wider vision to reconnect urban spaces, promote sustainable living, and demonstrate London's leadership in modern urban engineering. The project, while ambitious, mirrors a broader commitment across the city to place critical road networks underground, freeing the surface for greener, more vibrant communities.

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Source: Noah Wire Services