Local roads and the climate challenge

 

The local road network has little resilience against the impacts current weather conditions let alone the extreme weather events resulting from predicted climate change.

Under Review

The Government has recently undertaken a consultation on the UK’s infrastructure resilience, commissioned by chancellor Philip Hammond and carried out by the National Infrastructure Commission earlier this year.

”Local
Mike Harper, RSTA chief executive and director

It examined what needs to be done to ensure that the UK’s infrastructure can cope with the impacts of climate change, increased capacity demands and new digital technology developments. The information and evidence gained will be used to develop a new resilience framework that will be used for the next National Infrastructure Framework, due later this year.

ALARMing Evidence

The evidence for the local road network will show a transport system that, despite its importance to the national economic and social wellbeing, suffers from long-term under-investment, the result of which means it can barely cope with the climate pressures of today let alone those predicted for the future.

The poor state of the local road network was underlined by the latest Asphalt Industry Alliance ALARM Survey which found that it would cost £9.79bn the bring the  network up to a reasonable standard and that one in five roads – 20% – in England and Wales may need to be replaced within the next 5 years due to their poor structural condition.

The survey also reported that the total number of potholes filled in jumped by 24%, from 1.5 million in 2017, to more than 1.86 million in 2018. This is nothing to cheer about – we are essentially only managing the extent to which we have failed to effectively maintain our highway assets.

Given that roads are only resurfaced every 67 years on average it is not surprising that the local road network continues to deteriorate and has little resilience to the severe weather events predicted as a result of climate change.

Maintaining the asset

Potholes are symptomatic of roads that cannot be retained to the required standard due to insufficient funding for planned programmes of maintenance. They are formed by water entering the asphalt surface and the subsequent effect of both traffic load and frost action.

Surface dressing has been used in the UK with great effect for over 100 years to seal local roads against water ingress and to protect them from deterioration – this is the only reason that roads can last as long as 67 years between major resurfacing work.

However, the effectiveness of surface dressing (both in terms of cost and performance) is being forgotten with the race to fill holes to appease road users and cabinet members, rather than do the preventative work in the first place.

Surface dressing volumes have decreased from around 80 million square metres per annum three years ago, to around 65 million square metres of roads treated last year. During the same period, there has been an explosion in potholes.

These two things are directly related. If we want to provide better service to road users, and deliver on the Well-managed Highway Infrastructure code of practice and the guidance from the sector-led Highways Maintenance Efficiency Programme (HMEP), we need to get back to planned programmes of surface treatments that provide cost-effective and long-term protection to our highway surfaces.

For the cost of filling a single pothole of half square metre pothole reactively, we could proactively treat 15 square metres of road surface (30x the area) and protect it from pothole formation for 10 years.

Whatever the weather

Recent years have shown just how disruptive severe weather events can be. The winter of 2009/2010 was the coldest for 37 years. The cold, lengthy winter compounded the problem of the backlog of structural maintenance and renewal of roads. This left many roads less resilient and more prone to damage. Last winter was not particularly severe, yet over 1.8 million potholes were filled in.

Heavy rain and flooding also test the resilience of roads. It is predicted that climate change will result in increased heavy rainfall events. If roads are not structurally sound then flooding can weaken their foundations and the road surface will be damaged.

Heatwaves too are a potential problem for roads. The heatwave of 2003 cost £49.6m of necessary road repairs, £3.6m of which was needed for Oxfordshire alone.

Most roads will not begin to soften until they hit a temperature of around 50°C. However, even a sunny day in the 20°C can be enough to generate 50°C on the ground as the dark asphalt road surface absorbs a lot of heat and this builds up during the day with the hottest period between noon and 5pm.

When temperatures regularly reach the high 20°C, the bitumen in some road surfaces may soften and rise to the top. This makes the road surface sticky and more susceptible to pressure loads from heavy vehicles, resulting in surface ridging and rutting. The response from local highway authorities is to send out gritters to spread granite dust to absorb the soft bitumen and so stabilise the road surface and make it less sticky.

New specifications and management

Following a heatwave in 1995, the road industry introduced a new asphalt specification, introducing the use of polymer modified binders in hot rolled asphalt. These polymers raise the asphalt road surface softening point to around 80°C, which prevents it from softening under extreme hot weather.

Other asphalt products such as thin surface course systems also normally contain polymer modified binders. However, such modified asphalts tend to be more expensive and are generally only used on heavily-trafficked roads such as the motorway and trunk network of which only 50% is surfaced with the most heat resilient material. The percentage of local roads treated with heat resilient asphalts is much less at an estimated 5%.

The widespread adoption of asset management principles by local authorities should provide them with a better understanding of the condition and resilience of its road network. The data gathered by asset management plans should be used to develop an associated Resilience Plan, which would highlight potential problem roads, the need for structural or road surface interventions or alternative traffic management arrangements.

The resilience plan should also include a ‘critical network’ of those roads that have an economic and social priority to keep open. Unfortunately, given the lack of government funding for local road maintenance, it will be inevitable that there be less focus on less important ‘B’, ‘C’ and unclassified roads.

Conclusion

The Government must understand that the local road network is too economically and socially important not to have the necessary investment to make it more resilient to future extreme weather events. Yet funding is only £21,000 per mile for local roads compared with £1.1m per mile for the strategic road network.

In addition, the strategic road network has a five-year funding settlement allowing for the longer term planning necessary to plan for resilience whereas the local road network still relies on annual funding allocations from councils that can divert the cash to other local authority needs like social care.

If we are going to ensure resilience for the local road network, we need a five-year funding settlement that is ringfenced, so that the work can be planned and carried out accordingly.

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