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Outline

The resilience of transport infrastructures aims to ensure that road networks can resist possible impacts produced by external events (including climatic ones) without suffering major damage; and if they do occur, being able to recover as quickly as possible. Impacts resulting from climatic events are frequent on the road network. The region of Cantabria, located in the north of Spain, has a great deal of experience in programming actions to increase the resilience of the network (Collazos et al, 2022). This experience continues to grow and is allowing the validation and fine-tuning of the methodology for the assessment of risks associated with climate change in the state road network RCE (Alonso et al, 2022), contributing significantly to the identification of impacts and implementation of adaptation measures, as well as their quantification (sensitivity, probability, severity and criticality).

The pilot study in which we analysed two assets is in the Autonomous Community of Cantabria (see Figure 1): A67 (Cutting_A67_km175) and N623 (Cutting_N623_km117) roads.

Figure 1.- Location of the two assets studied within the region of Cantabria

Analysis of climate hazards

Hazard assessment refers to the identification and analysis of the different variables that might affect a road element or road service. In a broad sense, within the scope of the Spanish methodology, a hazard would be any event triggered by a climatic variable (e.g. flood; snow avalanche) or combination of climatic circumstances (e.g heat wave; intense rainfall after a drought period). A hazard will cause a potential impact (e.g. rock fall caused by intense rainfall; traffic disruption caused by river flooding).

The hazard assessment will be performed by:

• Analyzing relevant climatic variables that affect failure modes for the road elements or road sections studied (present and future projections).
• Checking or developing hazard maps (also present and future projections).

In this case study, the most important hazard identified is landslides due to intense rainfall. The main reference for carrying out these studies is AdapteCCa, although there are other sources of information, such as, Copernicus and the National Flood Zone Mapping System (SNCZI), that enable the characterisation of impacts and threats. In this pilot study the climate variable analysed is precipitation, specifically PMax24h (Figure 2).

Figure 2.- Maximum P24h Hazard map

Resilience assessment

The vulnerability assessment is based on the exposure, sensitivity and adaptive capacity of the assets or services. The concept of sensitivity refers to the intrinsic characteristics of the asset or service, including its adaptive capacity. A specific assessment of the sensitivity within the case study has been done, by using the matrixes that have been developed within the methodology. Both slopes were classified as “high vulnerable”. Assessing exposure consists of determining the extent to which an asset or service, by virtue of its geographical location, may be affected by the different potential threats that are being assessed. This has been done considering the hazard map (Figure 2). The exposure for both assets was “Very high”.

Because the vulnerability levels were high, a risk assessment was undertaken. The risk assessment is based on the probability and severity of the impact on the assets or services.  In this case study, probability was studied by considering the return periods for P24h in the zone. Severity was calculated by using the criteria established in the methodology, considering the population affected and average daily traffic, amongst others. The result was that the risk level was high for the A-67 km 175 and medium for the N-623 km 117.

Finally, for those assets or sections that present a high level of risk, an adaptation plan should be defined. The information obtained will provide road managers (administrations and companies) with analytical tools to help increase the network’s resilience, in order to prevent accidents or reduce the impact that meteorological conditions (both normal and extreme, and both now and for the time frames assessed) are having on the road infrastructure. During this phase we aim to identify and select a number of adaptation measures for particular case studies, while remaining aware of the fact that for each risk there are adaptation measures that may be specific or, in some cases, complementary.

How are adaptation solutions considered?

Adaptation measures have been implemented by choosing the best technical solution, given the hazards. In the figure below (Figure 3) it can be seen the landslide occurred in the asset studied (N-623 km 117).

Figure 3.- Landslide caused by heavy rains, causing the total cut of the N-623 and N-623a road in the afternoon of 10 March 2016. PK 117+300 left side

In the case of the A-67, the solution consisted of securing the head of the slope of a green wall with a reinforcement system consisting of a volumetric three-dimensional geogrid, triple reinforcement mesh and 16 mm diameter steel cable, forming 8×3 m triangulations, all anchored to the ground by means of self-drilling bolts and cable nets (Figure 4).

Figure 4.- Green wall with self-drilling bolts in A-67 highway

It should be desirable to consider a handbook of adaptation measures, describing benefits, places where it has been implemented, costs and possible disadvantages. Also, a CBA (Cost Benefit Analysis) should be undertaken to select the best option.

Co-benefits

One of the main benefits after the implementation of the dynamic screens has been the reduction in some sections of up to 74% of rockfall, as well as the increase in road safety due to the reduction of aquaplaning in some areas.

How is the adaptation strategy implemented in practice?

In practice, this is not an adaptation strategy as such. The NRA is responsible for the maintenance and exploitation of certain road networks. Therefore, they are aware of the main hazards and impacts and they design and plan the road maintenance with the purpose of reducing them.

Currently, the NRA is in the process of initiating specific studies aimed at proposing an adaptation strategy for the main road network in Spain.

Lessons learned?

Over the last few years, technicians of the Spanish Road Directorate in the region of Cantabria have identified through their expert judgment those elements most exposed in their network and have experience in preventive maintenance and emergency actions. Different mitigation and adaptation measures have been used, but it has been identified that data should be properly recorded. This would contribute to creating a database of climate-related events that would help to improve vulnerability and risk assessments. It has also been detected that Asset inventories have great room for improvement. Moreover, this would facilitate information management, and quantifying and monetizing measures, by collecting economic data from costs of different actions carried out, which would help influence, and objectify, from an economic point of view, the importance of increasing network resilience from the basis of a cost-benefit analysis based on lessons learnt.

In the future, the implementation of monitoring, early warning systems, and tools for sharing information with end users will be required, which will contribute to transparency and dissemination of information, ultimately facilitating civil society engagement.

These actions, if evaluated at a network level and counting on the participation of all the stakeholders affected, will set the basis for a more resilient road transport system. To achieve this goal, the following additional actions are proposed:

• Creation of a database of climate-related events in the road network. This database will contain information related to the road asset affected, the climatic event that caused the impact and the consequences.
• Creation of a repository where the different adaptation measures implemented are documented, together with periodic updates on its efficiency.
• Dissemination of the results achieved so far.