Transport Sector Briefing

1. Risks to infrastructure networks (water, energy, transport, ICT) from cascading failures (I1)

Vulnerabilities on one infrastructure network can cause problems on others, and transport infrastructure represents a significant part of this system.

Recent research conducted to support the CCRA has indicated that the vulnerability of interconnected systems may be significantly underestimated. The risk of network failures is already high, potentially affecting hundreds of thousands or millions of people per year.

Examples of cascading failures for transport include flooding of electricity substations disrupting air travel, heatwave impacts on IT and communications services causing freight and travel delays, and (recently) impacts on one transport system e.g. canal breaches, damaging another e.g., flooding of railways.

Transport networks are critical during emergency management and recovery, providing access to hospitals and for repairs to other infrastructure assets.

Adaptation actions tend to tackle individual risks on individual networks, rather than addressing the interconnected nature of infrastructure systems.

The magnitude of this risk is high both now and in the future across all four countries.

2. Risks to infrastructure services from river, surface water and groundwater flooding (I2)

Extreme rainfall events cause flooding of transport infrastructure and hubs, resulting in travel and freight delays, accidents and impacts on emergency services.

Currently transport infrastructure faces greater exposure to surface water flooding than river flooding. For example, 596 railway stations and 3,544km of rail network are at risk from surface water flooding across the UK compared to 81 railway stations and 1,144km of rail network at risk from river flooding.

Many high-profile flood events have disrupted transport services, such as the impacts of storms Ciara and Dennis in 2020 on road, rail and air travel.

Between 2006 and 2016 flooding caused an average of approximately £15 million in annual compensation payments between Network Rail and Train Operating Companies (TOCs).

Transport infrastructure of all kinds continues to face an increased exposure to surface water flooding in future. Railways will also increasingly be exposed to river flooding.

The current and future magnitude of risk is high across all four nations.

3. Risks to infrastructure services from coastal flooding and erosion (I3)

Sea levels are currently rising and the rate of rise is accelerating, including around the UK. Coastal flooding and erosion risk to infrastructure services, including those associated with the transport sector, will therefore grow.

The consequences of coastal flooding have been tempered over time due to improvements in flood defences, together with advances in flood forecasting, warning and emergency response and spatial planning. Despite this, notable coastal flooding incidents have still occurred that have significantly impacted infrastructure, and assets remain located in low lying coastal areas which will be threatened in the event of a defence failure. In particular, the railway network is vulnerable at key locations across the four UK nations.

The magnitude of risk is medium both now and in future for all four nations. Analysis shows coastal adaptation is an extremely cost-effective response, reducing residual damage costs down to very low levels. This is especially important as the risk of coastal flooding will increase as sea level continues to rise. Current projections show the likely change to be between 0.27 and 1.12 metres by the end of the century.

4. Risks to bridges and pipelines from flooding and erosion (I4)

Bridges are critical transport assets. Flooding and erosion or scour (the eroding of soil around bridge foundations) due to increased rainfall can lead to travel disruption, significant repair costs and the potential isolation of remote communities.

Bridges also have significant potential for lock-in of climate risks due to their long service lives (often exceeding 100 years), and high cost of retrofitting, making them priority assets for adaptation.

There are significant uncertainties about the structural integrity of road and rail bridges, many of which were built without consideration of future climate change. Greater winter precipitation and river flows will increase scour, potentially increasing the rate of failure of bridges in the UK.

Both bridges and pipelines are also affected by road transport, such as flooding impacting the ability of engineers to access and repair assets.

Currently, there are no quantitative assessments of climate change impacts on pipelines. The magnitude of risk is classified as medium now and in future for all four countries, but confidence in the assessment is low.

5. Risks to transport networks from slope and embankment failure (I5)

There are around 20,000 km of slopes and embankments supporting the UK’s transport infrastructure. Deterioration and failure of these assets have significant negative impacts on transport networks through damage, travel delays and accidents.

A tragic recent example from 2020 was near Stonehaven, where a passenger train hit a landslip following heavy rain and derailed, resulting in loss of life.

It is known that older, less well compacted assets such as those supporting the rail network are deteriorating at a faster rate than newer assets built to more modern standards. Between 2003 and 2014 there were, on average, 67 earthwork failures a year across the rail network in Scotland, England and Wales. Increases in high rainfall and soil moisture fluctuations combined with periods of dry weather and subsequent cracking are expected to lead to an increase in failures across transport assets. There are implications for more rural areas of the UK, where transport infrastructure systems are less resilient, and often follow natural features such as steep-sided river valleys prone to landslides.

The current magnitude of risk is medium now and in future for all four nations. The cost of adaptation measures across rail and road networks is usually offset by reduced repair costs and travel delays.

6. Risks to subterranean and surface infrastructure from subsidence (I7)

Ground subsidence is often due to shrinkage and swelling of clay soils, with damage to infrastructure occurring because of interaction with vegetation and associated water content changes. This form of subsidence is regarded as the most damaging geological hazard in Britain today.

22% of Category 1 rail lines, 29% of major train stations and 9% of the major road network are in areas of high susceptibility for shrink-swell subsidence. This can disrupt rail track alignment, leading to speed restrictions and travel disruption, and damage highway pavements, though this is considered a lower risk due to more modern compaction methods being used for construction of the road network.

Network Rail reported £40m in costs due to subsidence in the period 2006 – 2016 and, whilst subsidence was not one of the most frequent weather-related events, it was amongst the highest in terms of costs per incident.

The formation of sinkholes under road and rail infrastructure can result from prolonged or extreme rainfall, particularly in vulnerable areas underlain by soluble rocks.

Water, gas and electricity pipelines are frequently co-located beneath or alongside transport corridors, which can result in interacting risks.

For example, shrink-swell fracturing can occur in a water pipe, leading to local flooding and erosion, potentially forming a sinkhole impacting on nearby roads.

The current overall risk is deemed low rising to medium from the 2050s across the UK.

7. Risks to transport from high and low temperatures, high winds, lightning (I12)

Evidence that demonstrates the impacts of extreme temperatures, high winds and lightning strikes on rail, road, air and water transport networks is plentiful. Documented impacts include:

• High temperatures: buckling of rail lines, line sag and rail speed restrictions, damage to bridges and pavements, deterioration of airport runways, road surfaces and disruption of communications and IT services leading to transport delays. The impact of high temperatures on the rail network was responsible for over £20 million in compensation payments to TOCs between 2006 and 2016. High temperatures also result in exposure of outdoor transport staff to heat stress.
• High winds leading to disruption of rail operations due to debris on lines, damage to road infrastructure, closure of bridges, and suspension of port and vessel operations. Wind accounted for approximately £145 million in compensation payments between Network Rail and TOCs between 2006 and 2016. High-sided vehicles also become unstable in gusts of wind over 45mph, particularly on exposed bridges.
• Lightning strikes on railways damaging electronic equipment, line-side trees and buildings, and causing line-side fires. £40 million was paid in compensation payments to TOCs due to the impact of lightning on the rail network between 2006 and 2016.

Modelling suggests a worsening of many of these risks under future climate change scenarios, though the changing risks from extreme winds and lightning are difficult to estimate. Local roads are particularly vulnerable as they make up the vast majority of the UK’s road network, cover a wide range of geographic locations with more varied microclimates. The magnitude of the risk is considered medium at present, rising to high across the UK from the 2050s. Although there are examples of good practice within individual transport modes, the approach to managing climate risks across transport infrastructure is not yet being undertaken from a mobility or whole-systems perspective.

Assessment of the risk for future electrified transport systems that will be required to meet the UK’s Net Zero emissions commitments will be important.