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Climate change: are our roads resilient?

Last week, the EU’s climate change service reported that for the first time, global warming had reached 1.52 degrees C for the 12 months between February 2023 and January 2024. The world’s average sea surface temperature is at its highest ever level too: 21.05 degrees C on 3 February, above the previous peak of 21.02 degrees C on 23 August 2023.

Although the impacts of these rises are more devastating in poorer parts of the world, we are feeling the effects in the UK too. Storm Henk in January this year was the latest cause of flooding and evacuations. While last September, the Met Office reported a heatwave, with temperatures exceeding 30 degrees C somewhere in the UK for seven consecutive days.

These extreme weather events, together with creeping rises in temperature, will impact on our road networks – which are vital for communities, society and for the economy. To ensure that they remain resilient, road authorities will need to make changes to the way they are designed, maintained and the materials used.

The Mayor of London was so concerned about the issue of resilience that he commissioned an independent review, charged with recommendations on how London should prepare for extreme weather. The London Climate Resilience Review published its interim report on 17 January 2024.

The report is not complimentary about Central Government, calling out a lack of strategic vision. Emma Howard Boyd CBE, chair of the Review, said: “In the absence of national leadership, regional government has a more significant role to play. We need pace not perfection. It’s time for the UK, led by its cities and regions, to take action and prioritise adaptation.”

What is a resilient road?

A resilient road network is one that provides continuity of service, recovering quickly from climate change impacts so that disruption to its users is minimised. If maintenance and whole life costs are already high for a road network, the likelihood is that it is not going to be resilient.

Some of the impacts of our changing climate on our roads are already evident. Higher intensity periods of rainfall accelerate the formation of potholes. For some country roads, the ground beneath the road partially washes away leading to cracking, damage and potholes.

In its Task Force on Climate-related Financial Disclosures Report 2023, National Highways lays out some of the future risks it sees from climate change. For flooding these include over-capacity drains causing roads to flood, excessive water soaking into the road layers, saturated embankments slipping and bridge foundations in rivers washing away. Hot weather risks identified were asphalt surfaces deforming, freshly laid asphalt taking longer to cool and damage to bridge expansion joints.

Very high temperatures can mean that asphalt softens making it more likely to rut or for the bitumen to ‘bleed’ out of the surface. Even if it doesn’t soften, higher temperatures can increase the ageing process where the bitumen oxidises and becomes more brittle, meaning that damage from traffic will accelerate. Increases in intense rainfall can lead to water damage of the asphalt and can reduce the bearing capacity of lower layers of the pavement.

Climate-ADAPT, an information platform set up by the European Commission and the European Environment Agency says that new standards will be needed to increase the resilience of road transport. It suggests adjusting mix designs to use bitumen with a higher softening point, which could be achieved by modifying it with polymers.

Climate-ADAPT also mentions changing the structural design of pavements – how many layers, how thick and how composed. And it says surfaces could be cooled by increasing the reflectance of the road or by cooling them with water.

As for coping with increased amounts of water, Climate-ADAPT mentions the use of permeable pavements or porous top layers - already commonplace in the Netherlands – which direct water to the side of the road. It also calls for the development of hydrophobic coatings at a surface or micro-mechanical level.

But…resilience costs

Of course, creating resilience takes time and money. Local authorities are already stretched on resource and budget, without adding to their workload.

One of the recommendations for Central Government in The London Climate Resilience Review interim report is that it increases fiscal devolution for regional and local governments to accelerate climate adaptation. If climate adaption becomes a statutory requirement, funds should be distributed in line with vulnerability, it says.

However, with both the Government and the Opposition pulling back from investments in decarbonisation, and growing the green economy, it remains to be seen whether anyone will pay attention. Making roads more resilient will require even more investment if we leave it too late. We can already see the evidence of that in the underfunding of road maintenance and the resulting pothole backlog.


Thermal Road Repairs: Decarbonising the asphalt repair industry



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