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Impact of extreme weather phenomena on European transport system

First publishedin ITS International
2011 July August
The VTT Technical Research Centre of Finland's Pekka Leviäkangas writes about the initial results of the EWENT project, which was set up to research the effects of severe weather on the European transport network

The European EWENT (Extreme Weather impacts on European Networks of Transport) project, financed by the European Commission under 7th Framework Programme for Research, recently issued its first Work Package (WP1) report. This is a review of extreme weather phenomena and their effects on the European transport system across all modes.

Critical threshold values for the most relevant weather phenomena are listed following an extensive literature review.

The phenomena have impacts and consequences which result in deterioration in the service level of transport systems, and a dozen different impact mechanisms are charted and annexed to this report.

The report finds that precipitation in all its forms (rain, snow and hail) causes the most harmful impacts and that the road transport system seems to be the most vulnerable of modes.

Weather has always been an external factor affecting transport systems however, prior to climate change achieving political prominence, there has been surprisingly little research undertaken into its true effects. Our weather resilience is not perhaps what it should be in a modern society where mobility is a basic need that should be very predictable and reliable.


WP1 stared with a review of literature and the existing body of knowledge. Three sources were used: professional and scientific literature; media-reported cases; and detailed descriptions of extreme weather cases.

The second step was based on those outcomes. Critical weather phenomena and their parameter values were identified and assessed. These values form the decisionmaking criteria for EWENT's analysis on ex ante meteorological conditions. That is, threshold values for extreme weather phenomena are fixed in order to see how much the probabilities of occurrence will change, and future weather scenarios will be derived in EWENT's next stages.

The third set of results was the causal maps starting with weather phenomena and ending with consequences. However, the consequences were not yet quantified.

There are a few impact assessment model types that are available for further analysis (Table 1).

Model Type 


Data need examples
Empirically validated, widely accepted model; produces results in "what-if" scenarios

Known input variables

Empirically validated, but the model validity is discussed or criticised; not widely accepted; can be used for ex ante scenario work

Suggested input variables validated

Continuation of empirical experience e.g. trend models; not valid if the underlying dependencies or mechanisms change

Historical data, time series  unvalidated   

The dependencies can be illustrated or described but not analytically quantified

No explicit or immediate data needs some historical data or prior studies may back the argumentation data serving deduction and induction;
The model appeals to perception of the reality and included associations between associated phenomena.

interviews and gathering of insights and experiences and other qualitative data usually utilised extensively
Table 1: Impact assessment model types (Leviäkangas & Hautala, 2009)

All aspects and functions of the transport system are affected, but in different ways in different parts of Europe and on different timescales when one considers operations and infrastructure.

Operations can always be more or less flexibly adapted to a changed situation, but making infrastructure weather-resilient requires long-term planning.

The research group looked for the weather phenomena which on the basis of media reports, literature and case studies seem to affect the transport system the most. Their summary can be regarded as an empirical-heuristic conclusion: empirical in that it relies on past events and recorded incidents and studies; heuristic in that it cannot be claimed that there will not be other phenomena which require greater attention - it is simply the current presumption of the research group.

The report concludes with an 'extreme weather impact map' which is definitely an oversimplification but is nonetheless adopted to visualise where the top priorities are and what they should be. The consequences are prioritised as follows: 1st priority (accidents leading to casualties and injuries (A)); 2nd priority (Infrastructure collapse or damage (I)); 3rd priority (Time delays (T)); and 4th priority (Sub-optimal operations (O)).
[ Zoom ]
 EWENT project was set up to research the effects of severe weather on transport systems in Europe
Figure 1: Summary of critical weather phenomena in Europe
Figure 1 summarises critical weather phenomena, their occurrence by region, where their effects are the most severe, the most affected modes of transport and the consequences. The weather phenomena symbolised on the map are those identified as the most common extremes with identifiable consequences, for example heavy rain, heavy snowfall, extreme winds, extreme heat, drought and visibility.


Identifying the most critical phenomena is relatively easy: precipitation in all its forms very quickly affects all land transport modes and when precipitation comes as snow, aviation is also affected.

Precipitation also affects inland waterway transport operations significantly. For land transport modes, precipitation has a similar type of impact in all regions.

Excessive rain and snow also block urban transportation more effectively than any other weather phenomena.

When heavy snowfall is encountered, the only essential difference between regions is the availability of snow removal and maintenance equipment (and studded tyres in the Nordic countries). Furthermore, snow and ice in particular cause severe road accidents, the consequences of which should be considered a priority. This being so, the greatest responsibility for mitigation probably falls on road infrastructure owners and managers. How effectively they will be able to answer this challenge in terms of resources and preparedness is another matter. Even relatively modest but frequent flooding quickly deteriorates land structures over the years, although a single event does not in itself appear to be very serious.

There are self-evident reasons for road transportation being the most vulnerable mode. First, the traffic volumes are highest on roads and capacity is usually limited in densely populated areas. One relatively insignificant crash can quickly create chaos.

Second, road traffic is the least controllable and manageable. Where air traffic control or a railway traffic management centre can quickly decide on and execute adaptive and corrective measures, road traffic remains a slowly self-adaptive system that is geographically widespread and scattered.

As to climatological regions, most of the reported cases from both the literature and media reports seem to come from mainland Europe, the UK and Scandinavia. Most likely this is partly dependent on active research and active media in those regions. In this sense, the summary of results could underestimate weather phenomena such as heatwaves and sandstorms, which are common in southern parts of the EU. This bias is considered, however, to be insignificant in terms of the overall conclusions.

Initial thoughts

Two tentative strategic options seem to arise and be distinguishable in a broad sense for decision-makers responsible for adapting to and mitigating extreme weather consequences.

We could focus our efforts on those modes and places that are already quite well controlled, such as railways and aviation, and enhance their resilience.

These modes can then serve as back-up systems when other modes (roads) fail.

This could well be a cost- and resourceefficient option.

Or, we can start working on the road mode, trying to increase its resilience in different ways such as improving maintenance preparedness and road traffic control and information services. Vehicle manufacturers have already been active in developing anti-skid systems that are definitely useful on ice and snow. Relying on driver support systems and information services probably puts the onus (both effort and cost) on the user rather than on the public sector.

The above options are, however, very preliminary thoughts on how to conduct the battle against extreme weather impacts. For both strategies there are pros and cons (Table 2). If both strategies are implemented simultaneously, there is a risk of inefficient division of effort and resource. This risk is enhanced when international joint efforts are considered.

Inland waterways and short-sea shipping are special cases, and without underestimating their importance they are probably in a better position to withstand extreme weather events. Their share of the transportation market could even be increased and improved by recognising them as more weather-resilient modes that have greater reliability.

The role of ITS ITS has a key role to play when attempting to mitigate extreme weather impacts. The first and foremost is to warn those on the move and about to make a trip. The very old friends of ITS engineers, meteorologists, will most likely continue to be the best partners here. Weather-related services are always important and ITS business planners should utilise this everyday need that will not disappear with time; on the contrary, only the technologies, media and channels will change.

Another consideration is that ITS itself will become a victim of extreme weather.

Do we know how resilient our ITS is against extreme weather phenomena? Since ITS is strongly dependent on electricity and communications systems, it will need to be prepared for thunder storms and strong winds for example.

Greater consideration needs to be given to the phenomena most likely to cause problems and which sub-systems are likely to be the most vulnerable.


 Pros Cons
Much of the cost can be borne directly by the users, because users pay for in-vehicle safety systems and possibly also partly for information services.

The road system is the most "connecting" mode of transport - its reliability also serves the other modes best.

Investing in maintenance equipment and more comprehensive resilience traffic management is expensive and possibly not a very cost-efficient strategy.

The road system is a scattered system that is complex to manage and control.

Rail and aviation system resilience.
Rail and aviation systems are concentrated and centralised and manageable.

Mitigation and adaptation strategies are more easily implemented in centralised systems.

Aviation infrastructure owners and the aviation industry are obliged to bear much of the cost (which is then passed on to the consumer).

Both industries are in an economic pinch and introducing more obligations might further aggravate their situation.

For the rail sector some measures might require large public investments, which could be difficult to justify for a sector that already enjoys some public financial support.

Both rail and air travel chains almost without exception include stretches on roads and streets.
Table 2: The pros and cons of alternative strategic emphases

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