Resilience in transport infrastructure

Well-functioning and efficient roads and other transport infrastructure are essential for society to enable the delivery of goods and transport for work and leisure. With modern logistics chains based on just in time deliveries, this is more important still. Yet, roads and other transport systems do not cope well with extreme weather, whether through significant events such as the destruction of the sea wall and railway line in 2014 or through localised events such as small-scale flooding or damage to asphalt or buckling of railway tracks during hot weather.

Projections of climate change in Europe for the period 2071 to 2100 compared to the 1971 to 2000 period undertaken by the European Environment Agency in 2014 suggest that the whole of Europe will become warmer, with the greatest increases in temperature in the Mediterranean region, mountainous regions and the far north of Europe. For precipitation, whilst the Mediterranean region might become drier all year, perhaps by as much as 30% in southern Spain, much of Europe will have increased annual precipitation. However, with the exception of  Scandinavia and some Baltic states which are projected to have increased precipitation in the summer, the general trend is the increase in precipitation will not be evenly spread; for example much of France shows little of no change in annual precipitation but with a decrease of between 10 and  over 30% in summer; the UK and Ireland are predicted to have an increase of 5 – 10% annual precipitation but as much as a 20% decrease in summer precipitation in the south, with little change in the north. If the projections are correct and there are to be drier summers but increased overall precipitation, then logically the other seasons will be wetter. Some caution is required as not only are these long-term predictions, but there will remain natural variation in weather, so even if the general trend is correct, it doesn’t necessarily follow that every year will be wetter, or that every summer will be drier.

If the projections are correct, then there could be the following impacts on transport infrastructure:

  • Flooding from precipitation, rapid snow or ice melt, groundwater or sea level increase causing operational disruption, bridge scour, inundations of tunnels and increased landslides.
  • Saturation of unbound layers could lead to a loss of fine material and settlement or failure, whilst saturation of the subgrade could cause a reduction in strength.
  • Hotter, drier summers could lead to shrinkage in the sub-surface and induce cracking. Significant changes in soil moisture from very dry in the summer to extended saturation in the winter could be particularly damaging to road structures and embankments.
  • Other factors could be reduced vegetation on embankments due to higher temperatures followed by intense storm events increasing erosion or the potential for landslides.
  • Higher temperatures might make asphalt layers more susceptible to rutting and deformation or make newly laid asphalt workable for a longer time making it difficult to maintain profile during compaction.
  • A milder climate might cause an increase in the freeze-thaw processes in some northern or mountainous regions where the ground is currently frozen during winter which could damage the road infrastructure. Conversely, it might cause a reduction in freeze-thaw events in other areas which would be positive, and milder temperatures generally should lead to a reduction in winter maintenance requirements.

A warmer atmosphere holds more moisture – around 7% more per 10C increase in temperature[1], and can lead to an increase in the frequency and severity of storm events. Another longer-term impact of rising temperatures is sea-level rise caused by the melting of ice-sheets and glaciers. the European Environment Agency[2] predicts that sea-level rise will continue for many centuries even if greenhouse gas emissions and temperature are stabilised. The potential of storm surges and higher sea levels will threaten transport infrastructure in coastal and estuarine areas, and is of particular importance bearing in mind how many cities have been built up as a direct result of these locations for trade.

A quick look at the globe will identify many cities with populations of many millions that fall into this category, for example; the North Eastern Seaboard of the USA comprising Boston, New York, Philadelphia, Baltimore and Washington DC has a population of around 50 million, the wider Tokyo region has a population of around 40 million, the Pearl River Delta megacity including Guangzhou, Shenzen, Hong Kong has around 45 million inhabitants, and cities such as Shanghai (24.3 million), Mumbai (18.4 million) and low lying Dhaka (14 million). Whilst many of these already have protection measures in place, e.g. the Thames barrier in London to prevent storm surges, or have such strategic and economic importance such that investment would be forthcoming.

The challenge for all areas and for transport infrastructure is to understand the vulnerability identified by the Intergovernmental Panel on Climate Change as being an integrated measure of exposure, sensitivity and adaptive capacity. Adaptation efforts are difficult to predict in part because of a lack of clarify on the response of international governments in limiting greenhouse gas emissions, as well as industrial development and future technologies.

Whilst adaptation requirements over the long-term are difficult to predict, in the shorter-term there is a significant amount of R&D and also implementation of measures to assess the vulnerability, and improve the response of transport infrastructure to extreme weather events that occur today and are likely to increase.

The Forum of European Highway Research Laboratories (FEHRL) as part of its Forever Open Road (FOR) programme has published its Roadmap for the Resilient Road element of FOR, which is an update on the original 2013 document.

The document focusses on R&D requirements in three broad areas:

  1. Vulnerability Assessment and Identification of Adaptation Solutions
  2. Specific technical requirements for drainage, geotechnics, pavements and bridges and tunnels
  3. Changes to operational management and the regulatory framework

The original 2013 document set milestones for 2015, 2020 and 2025 focussing on development of single technologies, sub-system proving and implementation on a system level respectively. This update reflects on progress made against the 2015 milestones and resets the vision for 2020 and 2025 and looks towards demonstration projects and implementation of solutions.

The document provides information on four national projects that address various elements of the Resilient Road, namely R5G – the 5th Generation Road (France), R21C – Roads in the 21st Century (Germany) the E39 Coast Highway Route (Norway) and the Exploratory Advanced Research Programme (USA). Additionally, it lists over 30 projects identified that respond to various innovation themes of the Resilient Road as well as identifying a number of demonstration projects.

The FOR Programme doesn’t have any specific funds to undertake research but rather influences national and European research calls in the area and uses the FEHRL network to disseminate widely.

The 2017 Resilient Roadmap is available as a free download from the FEHRL website (www.fehrl.org). The Adaptable Road and Automated Road Roadmaps will be published in 2018.

[1] http://www.climatesignals.org/climate-signals/increased-atmospheric-moisture

[2] EEA (2017) Climate change, impact and vulnerability in Europe 2016. An indicator-based report