What Portland’s I-205 bridge cost blowout teaches London about mega-project risk

A major highway bridge project in Portland, Oregon, has seen its price tag balloon from the original £248 million approved in 2018 to an estimated £885 million – a jump of more than 250 percent. The I-205 Abernethy Bridge, operated by the Oregon Department of Transportation (ODOT), is now the fourth most expensive highway project per mile in the United States, behind only the neighbouring Interstate Bridge Project and the Rose Quarter scheme, both of which also face severe cost pressures.

For London readers, the Abernethy Bridge case matters not because of its location on the US West Coast but because it exemplifies a pattern of cost inflation, delayed ground works and strained contractor relations that has repeatedly afflicted large transport projects in the UK. Crossrail, the Elizabeth line, saw its budget rise from £14.8 billion to nearly £19 billion before opening three years late. The Lower Thames Crossing, should it proceed, is already running at an estimated £9 billion and rising. The Abernethy Bridge story offers a compact, well-documented case study of the same dynamics playing out at a smaller scale.

Por que importa

Key facts
| Metric | Value |
|——–|——-|
| Original approved cost (2018) | £248 million |
| Current estimated cost (2026) | £885 million |
| Cost increase | 257 percent |
| National rank (cost per mile) | 4th most expensive US highway project |
| Main contractor | Kiewit |
| Critical delayed component | Soil stabilisation, now estimated at £120 million |

A project that changed shape
The Abernethy Bridge carries Interstate 205 across the Willamette River south of Portland. ODOT originally sold the project as a seismic strengthening and widening scheme. By 2026, the cost had more than tripled. According to City Observatory, which tracks the project closely, ODOT is behind schedule and locked in a contract dispute with the construction firm Kiewit. The soil stabilisation component, a critical element for the bridge’s foundations, has been delayed and is now expected to cost around £120 million on its own.

Contexto

The per-mile cost now places the Abernethy Bridge behind only three other US highway projects, two of which are also in Oregon: the I-5 Interstate Bridge Project and the Rose Quarter widening. City Observatory describes this as a “terrifying precedent” for the likely trajectory of those two even larger schemes.

What this means for London’s infrastructure governance
London has its own history of transport projects that began with optimistic cost estimates and later required substantial top-ups. The Northern Line Extension to Battersea Power Station opened in 2021 at a final cost of £1.2 billion, roughly in line with its later-stage budget but significantly above early concept estimates. The Bakerloo Line Extension, still in development, has been costed at between £5 billion and £8 billion depending on the scope chosen, with no funding package yet in place. Transport for London’s recent financial constraints, combined with rising materials and labour costs, make the Abernethy Bridge pattern directly relevant.

The Portland case highlights three specific risks that London planners and policymakers should watch:

First, ground conditions. The soil stabilisation delay on the Abernethy Bridge is now a £120 million line item. In London, ground risk has been a major factor on projects such as Crossrail, where tunnelling through the capital’s variable geology – London Clay, Thanet Sand, chalk and alluvial deposits – contributed to delays and cost increases. Any major infrastructure scheme in the Thames corridor or along the proposed Crossrail 2 route will face similar subsurface uncertainty.

Second, contract disputes. ODOT and Kiewit are in a dispute that has slowed progress and added cost. In the UK, the collapse of Carillion in 2018 and the ongoing financial difficulties of major contractors have shown how fragile the delivery chain can be. TfL’s recent procurement for the Silvertown Tunnel and the Superloop bus network has been structured to spread risk, but the Abernethy Bridge case is a reminder that even well-capitalised contractors can end up in adversarial relationships with clients.

Third, the gap between initial and final cost. The original £248 million price tag for the Abernethy Bridge was the figure used to win political approval. By the time the project is complete, the final cost will be roughly three and a half times that. In London, the same pattern has been observed on smaller projects too: the Cycle Superhighway programme, the Bank junction upgrade and the Holborn gyratory removal all saw costs rise as detailed design and construction revealed complexities not captured in early estimates.

Access, not mobility
The City Observatory piece also includes a broader argument about transport priorities, citing urbanist Jon Boyd’s case that efficiency should be measured by access, not vehicle speed. Boyd argues that proximity – placing homes, shops, schools and workplaces close together – reduces the need for long trips and is fundamentally more efficient than moving cars faster over greater distances. This is a debate that has direct relevance to London’s current transport strategy, which emphasises active travel, public transport and the 15-minute neighbourhood concept.

The Mayor of London’s Transport Strategy, published in 2018 and updated since, already sets a target for 80 percent of all trips in London to be made by foot, cycle or public transport by 2041. The Abernethy Bridge case, where a highway project has become vastly more expensive while delivering exactly the kind of car-dependent mobility that Boyd critiques, reinforces the case for shifting investment toward local access and sustainable modes.

Parking costs and housing affordability
A separate study summarised by City Observatory examines the cost of mandatory parking minimums in US cities. Underground parking spaces now average £73,000 per space to construct, while aboveground parking averages £52,000 – a 50 percent increase after inflation since 2012. The report, cited by Ellen Schwartz of California YIMBY, finds that parking requirements add over 30 percent to the cost of constructing a studio or one-bedroom apartment in cities like Los Angeles.

In London, parking standards are set at the borough level and vary widely. Central London boroughs such as Camden, Islington and Westminster already restrict car parking in new developments, while outer London boroughs often require a minimum number of spaces. The US data underscores that parking mandates are not a free good: they add tens of thousands of pounds to the cost of every home, and the burden falls disproportionately on smaller, more affordable units. For London’s housing delivery targets – 66,000 homes per year according to the London Plan – reducing parking requirements could be a relatively low-cost way to lower construction costs and speed up delivery.

Built environment emissions
The City Observatory piece also argues that transport and building emissions should not be treated as separate silos. Lloyd Alter, writing in Carbon Upfront!, contends that electrifying vehicles without changing urban form ignores the embodied carbon of the entire system of heavy vehicles, highways and high-rise towers. He calls for eliminating single-family zoning, removing parking requirements and adopting 15-minute neighbourhood standards.

London’s climate targets require net-zero carbon emissions by 2030 for the GLA group and by 2050 for the city as a whole. The current approach separates transport emissions (managed by TfL) from building emissions (managed by borough planning departments and the GLA’s energy strategy). Alter’s argument suggests that this separation may be counterproductive. A planning decision that allows a car-dependent development on the urban fringe, even if the buildings themselves are energy-efficient, locks in high transport emissions for decades.

Source: City Observatory, The Week Observed: October 9, 2026, https://cityobservatory.org/the-week-observed-october-9-2026/

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