Future of Bridges

Will the next five years be a golden age for bridge engineering, or will inflation and skills shortages undermine the huge pipeline of work and progress towards net zero?

By 2027, we need to be doing things very differently. That is the central message from bridge engineers as they consider how to navigate the forthcoming raft of decarbonisation, productivity and technical challenges.

Not only will we be five years further down the road to hitting net zero targets, but the introduction in 2027 of the second generation of Eurocodes promises to change the landscape for bridge design.

“In many ways, the sense of urgency is very exciting as it gives us the opportunity to prove what we can do,” says WSP executive director and head of civil and bridge engineering Steve Denton.

In Hertfordshire we are expecting something like a 15% drop in our ability to build things

“We’ve always talked about the need to change and the opportunities for change – what I’m seeing now are some real imperatives. It could be a golden age for engineering.”

The wider economic landscape is one such factor. Denton continues: “We’ve been through a number of downturns in terms of the market. But they have always been demand-side challenges, now they are supply-side. Skilled bridge engineers are in high demand at the moment and I don’t see that diminishing. So we really need to embrace changes we’ve been talking about for years and these relate to productivity.”

He believes that incremental gains are the best way of achieving progress. “It’s not glamorous, but that’s where we will see the greatest gains – in attention to detail, willingness to improve and challenge ourselves – always questioning the ‘value-added’ in what we do and digging out wastefulness.”

Denton highlights the fact that in the medium term – by 2027 – the second generation of Eurocodes will be helping engineers work more efficiently. Ease of use is one of the key requirements for the new codes and he says improvements in clarity will reduce the number of errors and have a beneficial impact on quality of design and productivity.

“Ratification of the second generation Eurocode drafts is targeted to be complete by the end of 2025 and the new Eurocode standards will be with national standards bodies by 2026,” he says.

HS2 will build more than 500 bridge structures, including over 50 major viaducts

“By 2027 we need to have the new national annexes prepared and be deep into the process of educating designers about the changes and the opportunities they provide.”

But if the new Eurocodes can make bridge design more efficient, getting the projects off the drawing board could become more problematic as inflation takes hold.

The pipeline of bridge work is considerable, with the next Network Rail and National Highways five-year delivery plans kicking off in 2025 and 2026 respectively. There are also major projects including High Speed 2, the A66 Transpennine route and the M54/M6 link road.

Local authorities also have a huge portfolio of projects, although inflation is creating uncertainty warns association of directors of environment, economy, planning and transport (Adept) national bridges group chair Keith Harwood. He is also head of bridges at Hertfordshire County Council.

The uncertainty is not just whether the rate of inflation will continue to rise, but whether local authorities will receive more money to cover additional costs.

“The government has said it is committed to investing in infrastructure, but I’m concerned that will simply mean not cancelling projects that are already planned [rather than extra investment for new projects], which won’t help local authorities, won’t help carbon and won’t help maintenance,” he says.

“Every authority will be different but in Hertfordshire we are expecting something like a 15% drop in our ability to build things,” Harwood explains. “Roughly half of that is due to having to save money for other things, including interest on borrowing, and also having to cover our own inflation costs.”

But while inflation is causing some problems, engineers are excited about the challenge of reducing the carbon footprint of bridge projects.

The Net Zero Bridges Group was established in 2021 to check existing decarbonisation guidelines and advice for its relevance to bridge professionals. It also aims to accelerate progress towards net zero in the sector and share knowledge and data more widely.

Existing guidelines are largely aimed at the building sector, where operational performance is a significant factor. Embodied carbon has greater relevance to bridges, but the opportunities for reducing it are also more tightly constrained. The difference in design life is considerable – as much as 120 years for bridges against 30 for buildings.

Clients need to be prepared to reward innovation by allocating larger proportions of their budget to low carbon technologies

Low-carbon materials are available, but are in limited supply. Some, like cement replacement ground granulated blast-furnace slag (GGBS), a by-product of iron and steel making, will never be able to meet demand.

Net Zero Bridges Group chair Brian Duguid says the onus is on engineers to use less. “That could mean building fewer bridges, working harder to retain and conserve existing ones, or it could mean challenging the span – do we need a bridge or could we use a culvert or embankment instead?

“Then the focus is to shave off material by using different forms or better analysis, or by challenging the client brief or specification. We also need to work harder at reusing our existing assets,” he adds.

While reductions in embodied carbon at the design stage can be significant, gains from keeping bridges in service for longer are obvious.

“Managing and maintaining our existing infrastructure well, is one of the biggest contributions to carbon reduction that bridge engineers can make,” Denton claims.

But Harwood says making the case for cutting carbon is not straightforward: “The overriding concern for local authorities at the moment is cost, but the fact that we don’t fully understand the relationship between cost and carbon makes it difficult to make an informed choice.”

Better understanding of the condition of a bridge and the rate at which it is changing is crucial to engineers seeking to make bridge maintenance more efficient.

“There are exciting areas where we have proof of concept around artificial intelligence and digital imaging that can really help us get much better insight into how structures are changing over time,” says Denton.

“This area is ripe for disruption and I will be disappointed if we haven’t taken some significant strides by 2027.”

Harwood agrees: “There’s work to do on digital techniques in monitoring, so we can make more informed decisions about whether to do a full refurbishment, or just do emergency repairs and come back in five years’ time. I’m hopeful that monitoring technology will become a lot cheaper and more available over the next five years, with sensors being part of a bridge inspector’s toolkit, rather than a specialist service.”

By the time projects reach the construction stage, the extent to which contractors can influence carbon emissions tends to be limited to operational efficiencies. FCC Construcción UK business manager Mian Langellier says that construction efficiencies are not the whole story.

“Clients need to be prepared to reward innovation by allocating larger proportions of their budgetto low carbon technologies, including those to reduce embodied carbon in structures as well as those to reduce overall construction carbon footprint.”

Bridge owners dithering over decarbonisation are urged by heritage bridge maintenance body Rochester Bridge Trust (RBT) bridge clerk and chief executive Sue Threader to “just do it”.

The RBT is responsible for three historic bridges across the Medway in Kent. She routinely hears other bridge owners making excuses for failing to measure the carbon footprint of what they do, or insisting their suppliers and contractors do the same. Some claim their procurement procedures prevent it. Others that the tools do not exist yet or they are unable find the carbon factors they need. But Threader insists that these are not valid reasons for not getting started on cutting carbon.

She has every right to insist, having led RBT through its own route to net zero from a standing start in just two years. The realisation that this was something it should be doing only hit when the trust’s major bridge refurbishment contract, which involved the refurbishment of three bridges was already live. The project was completed in 2020.

RBT committed to calculate the carbon footprint of the entire project and plant trees to offset it. This required a steep learning curve but by referring to the available guidance and challenging materials suppliers, the trust was able to pinpoint the impact different decisions at the early stages could have had.

Relating each factor to the number of trees that would be needed to offset it was a hugely effective way of communicating the impact, to engineers as well as the public, Threader says.

Materials choices was one such factor – with aluminium one of the biggest contributors to the carbon footprint, opting for recycled rather than virgin material would have slashed the carbon cost, as would using stone from the trust’s own stores, even if it was not the best colour match.

The carbon cost of workforce travel was another revelation and one that Threader is determined to tackle on future contracts.

A “future ancient woodland” of 8,000 trees was planted on local land owned by the trust – 500 more than the estimated offset, to provide a surplus for future offsetting.

Since then the trust has achieved net zero on its routine bridge maintenance work and the baseline of 116 trees per year to offset its operations has been whittled down to just 11. Many of the changes are simple, Threader reveals. Bridge sweeping had the highest carbon cost, so its frequency was gradually reduced while observing the impact, to find the sweet spot. It is now done three days a week rather than seven. The timing and intensity of bridge lighting was reduced; electrical equipment replaced diesel – including the safety boat – and local staff commute on electric bikes that they charge using the trust’s renewable energy supply.

“If you scale up nationally the number of trees we had to plant on a single refurbishment contract to offset our impact, it gives you an idea of the size of the problem,” says Threader. “The process is not complicated, it’s just a giant spreadsheet, but we cannot afford not to be doing this, we can’t afford to wait for someone to issue a manual or instruct us to get on with it.”

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