Annex 1: Development of the Trunk Road Adaption Plan
This project developed a Trunk Road Adaptation Plan (TRAP) with the aim of enabling a well-adapted Trunk Road Network that is safe for all users, reliable for everyday journeys and resilient to weather-related disruption.
The approach is rooted in UK Climate Impacts Programme methods, and structured around the standard climate risk management project cycle with the following stages (below), with clear and early definition of the adaptation problem, followed by a series of screening, risk assessment and adaptation planning steps to inform the TRAP.
Figure 4 - Climate risk and adaptation development cycle with the following stages:
- Problem Definition
- Climate Screening
- Climate risk assessment
- Adaption planning
- Adaption monitoring
Supporting information, including present-day and future climate risk assessments, is drawn from a series of the three internal reports:
- Part I – Present-day climate screen, 2023
- Part II – Climate change risk assessment, 2024
- Part III – Climate adaptation plan, 2024
Present-day climate screen
The climate baseline assessment was predominantly undertaken as a GIS screening exercise of climate hazards (Met Office ‘HadUK-grid’ historical climate data, SEPA flood map layers and British Geological Survey geology layers) overlaid with TRN assets (roads, bridges and culverts) to understand exposure. Vulnerability was also considered in the screening based on asset management information including age of road surface and condition scores of structures.
Engagement with Transport Scotland stakeholders, analysis of Transport Scotland’s incident database, and previously identified vulnerable structures were all tasks undertaken as validation for the independent baseline screening approach.
The present-day screening assessment was undertaken to determine which areas of the Trunk Road Network are currently most exposed to climate hazards. The assessment considered hazard exposure and asset vulnerability to assign a high-level risk score to areas of the Scottish Trunk Road Network at a 2km hex resolution.
The identified geographical extents of flooding, scour and landslide (localised risks), by management area, provides useful information to inform decisions on proactive monitoring and prioritised management. This is also true for the identification of “hotspots” of higher risk associated with extreme hot and cold days and high winds; directing adaptation actions to the identified areas of higher risk provides an informed approach and will improve efficiency.
The primary findings of the present-day climate screening are presented in the table below, based on the length of road or number of structures within an identified risk area and a percentage of the network affected. A risk score has been assigned based on an assessment of past disruption events, the spatial analysis and stakeholder engagement outputs.
Table 2 - Present-day climate screen
Although the respective classifications are “Very High” and “High”, this assessment considers actual risk of extreme heat to the TRN to be significantly lower due to the low threshold value used in the screening assessment (days >25⁰C).
From the risk screening outputs, areas exposed to several climate hazards were assessed to identify potential Vulnerable Locations Across the network. Risk scores for eight climate hazards, considering hazard, exposure, and asset vulnerability, assessed across 2km side ‘hexes’, present the areas of the network subjected to the most risks in the figure below.
Figure 5 - Trunk Road Network multi-hazard score
Climate change risk assessment
To build on the assessment of exposure and vulnerability in the present-day screening assessment, the future climate change risk assessment utilised climate model (UKCP18) datasets, focused on medium (RCP6.0) and high (RCP8.5) emissions pathways for the 2050s and 2080s.
The risk assessment was further informed based on engagement with Transport Scotland’s stakeholders, flood map data (SEPA), Dynamic Coast (University of Glasgow) and literature review. Assessments were completed for nine key hazards, surface water flooding, river flooding, coastal flooding, river scour, landslides, extreme heat, cold spells, high winds, and cascading risks.
The future climate risk assessment was undertaken to determine the frequency of hazardous climatic conditions and the magnitude of impact. The assessment considered hazard likelihood and impacts to assign climate risk scores for the Scottish Trunk Road Network.
The assessment estimated the likelihood and impact of each hazard affecting the trunk road network. Summary scoring for each risk was undertaken with regard to the following risk scoring matrix, consistent with the Transport Scotland Roads Corporate Risk Register approach (Likelihood x Impact = Risk).
Table 3 - Risk assessment scoring matrix
| Risk | Perceived Materiality | Summary | % of cells in risk class >15 |
|---|---|---|---|
| River Flooding | High | 161.7km of road in SEPA medium fluvial floodplain 609 bridges and 105 culverts exposed. | 11% |
| Surface Flooding | High | 355.1km of road in SEPA medium fluvial floodplain 412 bridges and 85 culverts exposed. | 17% |
| Landslides | High | 786.3km of road in BGS Geosure "significant" landslide risk area | 7% |
| Coastal Flooding | Medium | 44.1km of road in SEPA medium fluvial floodplain 81 bridges and 2 culverts exposed. | <1% |
| River Scour | Medium | 147 structures identified within a SEPA >2.0m/s scour zone | 1% |
| Cold Spells | Medium | The North West and South East Management Areas most exposed | 26% |
| High Winds | Medium | The South West Management Area and coastal exposures were found to be most exposed | 24% |
| Warm Days* | Low | The South West and South East Management Areas, and around Glasgow were found to be most exposed. | 27% |
The assessment built on the transport risks identified in the Climate Change Committee’s Independent Assessment of UK Climate Risk (CCRA3), and Transport Scotland’s Roads Risk Register. A summary of key risks is presented below for the 2050s, based on a medium to high emissions scenario (RCP6.0).
Table 4 - Climate risk scorecard for the 2050s
| Risk description | Risk in 2050s |
|---|---|
| An increase in surface water flooding in Scotland due to heavy rainfall causing damage to assets, network disruptions and safety risks. | Very High |
| An increase in river flooding in Scotland due to heavy rainfall causing damage to assets, network disruptions and safety risks. | Very High |
| An increase in river scour conditions in Scotland due to climate change causing damage to assets, network disruptions and safety risks. | Very High |
| An increase in landslide events in Scotland due to increased likelihood of intense rainfall events with antecedent rainfall causing damage to assets, network disruptions and safety risks. | Very High |
| An increase in coastal flooding and erosion in Scotland due to sea level rise and storm events causing damage to assets, network disruptions and safety risks. | High |
| An increase in cascading failures due to climate change in Scotland triggering impacts across the TRN including damage to assets, network disruptions and safety risks. | High |
| A decrease in heavy snow fall and ice events in Scotland due to climate change, though an increase in event magnitude causing damage to assets, network disruptions and safety risks. | High |
| An increase in extreme wind conditions in Scotland due to climate change causing damage to assets, network disruptions and safety risks. | Moderate |
| An increase in extreme heat days (>30°C) in Scotland due to climate change causing damage to assets, network disruptions and safety risks. | Very Low |
Key risks included the risk of increased surface water flooding, river flooding, river scour and landslides due to climate change damaging assets, causing network disruption, and resulting in safety risks. It has been assumed in the risk ratings that current levels of adaptation continue in future e.g. the investment on flood defences and Transport Scotland maintenance of drainage systems.
Future climate risk scores were largely informed by threshold analysis of UKCP18 climate projections. An example of the mapped outputs that informed the future climate risk scores is presented in the figure below. This shows a gridded count of heavy and persistent rainfall that may lead to unstable ground conditions and landslide events.
Figure 6 - Number of days meeting landslide threshold between 2040 and 2059 (RCP6.0).
Estimated annual damages of future flooding events was also estimated for surface, river, and coastal flooding to inform the potential cost of future climate hazard events.
Climate adaptation plan
The adaptation plan brings together adaptation options to respond to the major risks, assessing options using multi-criteria analysis. Impacts and adaptation monitoring were also explored, suggesting practical adaptation indicators for monitoring adaptation progress.
The adaptation plan was informed by the present-day climate screen and future climate change risk assessment to identify priority areas for adaptation and recommend actions to build resilience across the Scottish Trunk Road Network.
The approach to delivering the TRAP included the following steps:
- Review of risks and vulnerabilities identified in the Climate Vulnerability and Risk Assessment.
- Stakeholder engagement to understand current actions and develop future recommendations.
- Definition of clear themes aligned with ACCAR Vision (Safe, Reliable, Resilient).
- Identify barriers to adaptation and enabling actions to overcome barriers.
- Consideration of co-benefits across all actions throughout the TRAP development.
Engagement consisted of collaborative workshops and targeted interviews, with multiple rounds for review. Stakeholders included Transport Scotland officials, Operating Companies representatives and other government agencies including representatives from Scottish Network Rail and Scottish Environmental Protection Agency (SEPA).
The Climate Adaptation Plan Report presents a full list of recommended actions, mapped against prioritised co-benefits. It also provides Transport Scotland with suggestions for developing a comprehensive adaptation monitoring framework and guidance for implementing site-specific dynamic adaptive pathways planning to improve adaptive management.
The results can inform and be integrated into the Transport Scotland Roads Corporate Risk Register, to ensure that climate resilience of the road network is outlined with greater confidence, supported by data and stakeholder engagement.
A description and consideration of the Adaptation and Enabler themes is presented below.
Adaptation themes
Recommendations that contribute toward improving adaptation have been grouped into three action themes: safety enhancement, reliability improvement and resilience building.
Table 5 - Adaptation Themes:
Safety Enhancement – 8 Recommendations
Recommendations for improving road safety related to climate change sit across ensuring road infrastructure is fit for purpose, properly maintained and in safe locations. Actions such as integration of weather forecasting systems to deliver early warning alerts, and robust communications with stakeholders, including the public, in the form of roadside messaging, text alerts and social media are also considered. By prioritizing adaptation measures and integrating climate resilience into road safety strategies, Transport Scotland can better safeguard lives and infrastructure in the face of climate change.
Reliability Improvement – 5 Recommendations
Reliability recommendations look to ensure a consistent and uninterrupted transport network, especially in the face of climate change. Actions include investing in proactive maintenance strategies to prevent road deterioration, implementing intelligent transportation systems that provide real-time information on road conditions and management of alternative routes to bypass closures or hazards. Furthermore, developing coordinated response to address disruptions swiftly and effectively when they do occur is a priority. By promoting reliability in road network management, transportation systems can better withstand the challenges posed by climate change and ensure uninterrupted mobility for people and goods.
Resilience Building – 11 Recommendations
Improving the overall resilience of road networks is a critical undertaking in safeguarding transportation infrastructure and ensuring the continued functionality of essential routes in the face of climate change. Recommendations for improving resilience include upgrading drainage systems or elevating critical infrastructure and promotion of catchment-scale flood management solutions. By prioritizing resilience, Transport Scotland can ensure the continued functionality of transportation systems.
Enabling themes
Recommendations that contribute toward enabling adaptation across Transport Scotland and its partners have been grouped into three Themes: Engagement and Partnership, Research and Understanding, and Monitoring and Evaluation.
Table 6 - Enabling themes:
Engagement and Partnership – 10 Recommendations
Collaboration between transportation agencies, urban planners, engineers, and environmental experts is essential for developing comprehensive resilience strategies and emergency response that address the multifaceted challenges posed by climate change. For example, collaboration with forecasting experts, government agencies and local authorities during Storm Babet ensured all the right expertise were together, with the best information, to make risk informed decisions and manage the impact on the TRN.
Research and Understanding – 7 Recommendations
The TRN climate risk assessment identified several gaps in understanding that would further inform the assessment in the future. Investing in research to further understand the location and impact of climate hazards is considered an important factor of this plan. Furthermore, innovation to develop new technologies and materials that better withstand extreme weather conditions helps to future-proof road infrastructure.
Monitoring and Evaluation – 4 Recommendations
A comprehensive monitoring framework, assessing both climate impacts and adaptation recommendations, allows for a baseline performance indicator to be established against the themes of Safety Enhancement, Reliability Improvement and Resilience Building. This shows Transport Scotland, and other parties outside the organisation, the direct effects of adaptation actions and indicates stepwise improvements in moving the TRN toward a well-adapted and prepared transport system.