Climate change and road traffic infrastructure
(Photo: Deutscher Wetterdienst)
In contrast to what many of us believe, our planet has never had a stable climate. In recent years, however, there has been a significant increase in average temperatures, and since the CO2 content in the atmosphere is continuing to increase, a further rise in temperatures is to be anticipated. The key issue is therefore: How will the climate change?
It is only possible to answer this question by using emission scenarios and climate models. Emission scenarios represent differing assumptions relating to the future economic development in the world, which are fed into the global climate models. The climate models are then used to quantify the effects of the scenarios. Although the climate projections created in this manner are thus subject to uncertainties, climate researchers agree that that the number of extreme weather events, such as heatwaves or heavy rainfall will increase in Germany.
An interdisciplinary working group has been set up in the BASt for the purpose of addressing the effects of climate change on road infrastructure and road traffic.
First of all, four pilot projects have been initiated in an initial approach to describe the influences of the changes to be expected in structures, the subsurface, embankments, road surfaces, traffic sign installations and drainage facilities.
What are the risks involved with the extreme weather conditions (heatwaves, storms) associated with climate change for bridge structures? Bridges possess a particularly long renewal cycle. It is not too early, however, to already consider climate forecasts both in forthcoming renewals and the planning of new bridges.
When turning, the road gradient swings from one side to the other. In the event of heavy rainfall, the thickness of the water film can exceed critical values at such "transverse gradient turns". The risk of accidents in wet conditions is up to five times higher than in dry conditions – particularly at curves in wide road surfaces, as is the case, for example, on motorways. It remains to be clarified whether more sections of road and critical places will be subject to the risk of aquaplaning due to heavy rainfall in the future than today.
According to climate projections, 30 percent more rainfall is expected in winter – while there will be longer heatwaves in summer. Both factors can lead to instabilities in embankments and slopes. It is intended to examine in an example region whether increases in earth slippages on roads can happen under the impact of the precipitation conditions to be expected.
Regionalised climate projections have to be mapped to the road network. For this purpose, queries to databases with different data formats have to ensue and linked via a geographical information system. This project provides an initial model to link technical data from road information systems with raster data from regional climate data. It allows the first queries on road equipment at specific locations taking account of the climatic changes projected there as a basis for corresponding risk analyses.
The results of these four pilot projects reveal that further research relating to the required adaptation measures for roads and engineering works are required into the consequences of climate change. Therefore a multi-stage approach with defined goals encompassing a period of 20 years has been developed in the Federal Highway Research Institute.
BASt roadmap milestones to adapt road traffic infrastructure to climate change
The complete implementation of this roadmap represents an extremely complex task, which is being developed in the overall research programme "Adapting road traffic infrastructure to climate change" ("AdSVIS" for short). The AdSVIS research programme currently consists of 15 sub-projects aimed at achieving the first milestones in 2014.
AdSVIS research programme
The project "Risk analysis of key freight and transit traffic axes taking seaports into account" (RIVA) is the central AdSVIS project. The aim of this project is to develop instruments for identifying, analysing and assessing the risks involved due to projected climate changes.
The project follows up on the ERA-NET ROAD Project RIMAROCC (Risk Management for Roads in a Changing Climate), in which conceptual foundations for consideration of such risks in relation to road infrastructure are drawn up. It has been necessary, however, to further develop this methodology for the complex road network existing in Germany. For this purpose, an MS-Excel-based tool was developed, into which standardised collected data (e.g. situation data) as well as data from climate projections were fed. This tool has, for example, been applied to some 10 percent of the German section of the Trans-European Transport Network (TEN-T).
The evaluation results generated using the RIVA methodology initially enable the climate-related risks to be prioritised. They can, however, also be drawn upon for a comparison with other risks for road infrastructure. The RIVA Project thus provides an important contribution both for the debate on risk management strategies and the decision-making on the measures necessary.
Investigation scope of the RIVA Project (source: Alfen Consult)
Networking and communication of the AdSVIS projects
All the AdSVIS projects are intended to be networked to each other so that both the results and interim results can already be exchanged during the duration of the individual projects, thus enabling these results to flow into the other projects. For example, areas, in which slope slippages are to be expected in the future (project: Assessment of slope slippages and creation of a hazard warning map), already flow into the RIVA Project risk analysis. All the results from the AdSVIS projects are intended to be presented at national and international events on a cross-project basis.
AdSVIS - Server
Practically all the AdSVIS projects require network data from the road infrastructure and climate projection data. Both the network data and the data for engineering works are contained in various databases. In order to avoid all the researchers having to familiarise themselves with various databases while still receiving the same project-relevant data, a central database is being set up to contain all this data. The climate projection data from various climate scenarios will be maintained here. This will enable all projects to draw on uniform underlying data and the results to be compared with each other. A further step is the integration of a digital terrain model. The integration of the digital terrain model is intended to allow a linking with data from projected rainfall events. This combination will enable the outflows from the projected rainfall events to be collected by the digital terrain model and endangered infrastructure identified.
Matching of meteorological measurement variables with raster data from climate projections
Weather stations are rarely to be found near roads and even climate projections only provide mean values for specific rasters, which are not dependent on the topography, land use or development works. This project is intended to create algorithms to match the data from weather stations (temperature rainfall) with the data on the roads, while taking account of the type of structure and circumstances of the road. A further step will be to make use of the algorithms to determine the climate influencing factors for the road traffic infrastructure elements from the raster-related climate projection data. In this manner, it will be possible to assess the effects of, say, a projected increase in mean annual temperature on the temperature behaviour of roads.
Development of influence models and input parameters for bridges and tunnel structures
The pilot project "Effects of climate change on existing prestressed concrete bridge structures" has revealed adjustment requirements – particularly for prestressed concrete frame bridges constructed before 1981. The project "Development of influence models and input parameters for bridges and tunnel structures" is intended to determine location-related and design-relevant climate parameters to enable a mapping of climate impact on structures in regions especially strongly affected by climate change under near-realistic conditions.
Vulnerability analysis of bridge and tunnel structures
This project is designed to produce a vulnerability analysis of bridge and tunnel structures, incorporating the various structural types and constructions as well as typical equipment elements. Operation-related situations, such as in tunnel structures, which can lead to critical operating situations due to extreme weather events, will also be taken into account. This investigation is designed to enable the identification of critical structures, so that appropriate measures can be undertaken to reduce the vulnerability of the structure. This can hereby lower the costs of repairing or replacing a damaged or destroyed structure.
Measures analysis to reduce the vulnerability of bridge and tunnel structures
Here it is intended to create a measures catalogue to reduce the vulnerability of bridge and tunnel structures for the structures identified in the project "Vulnerability analysis of bridge and tunnel structures". This analysis should take account of measures both for existing and future structures (constructional and organisational measures) as well as serve the measures catalogue of the federal states' road administration departments as a decision-making aid for new construction, repair or adaptation measures.
Assessing earth slippages and creating a hazard warning map
The pilot project "Assessing the risks of landslides and slope failures due to the increase in extreme weather events" consists of investigating earth slippages already occurred in three typical regional case studies, and conducting an exemplary assessment of the causes taking account of the climatic influences. In the current project, earth slippages in the whole of Germany are examined – incorporating not only the slope inclination but also other slippage-relevant factors, such as geology, geomorphology, groundwater, exposition and vegetation. Together with the climatic parameters, a climatic, geological engineering model to assess potential landslide-endangered areas up to 2100 is undergoing development, and a nationwide hazard warning map (risk map) created with designation of particularly landslide-endangered regions along the Federal Highway Network.
Assessing the dimensioning of road drainage facilities
The aim of this project is to test the current drainage facilities dimensioning approaches in accordance with the "Directives for Road Construction - Drainage Section" (RAS-Ew): and the "Directives for Construction Measures on Roads in Water Protection Areas" (RiStWag) in relation to the hydraulic performance for safeguarding soil and preventing water pollution and to the constructional work. The results of this research project will serve as the basis for revising the set of regulations.
Inventory of drainage facilities at selected TEN-T sections
As part of this project, information on drainage (open/closed), treatment and retention systems as well as pumping stations is being compiled and prepared in such a manner that it can be incorporated into the AdSVIS server and thus serve as underlying data for other projects, such as the RIVA Project. For the purpose of undertaking the risk analysis, it is necessary for the information on the drainage systems along the selected TEN-T sections to be taken into account.
Adapting the dimensioning of asphalt and concrete road surfacing
The methods used today to take account of the influence of weather when dimensioning road surfacing (both in new construction and in maintaining existing roads) are based on long-standing meteorological observation series. This project investigates the extent that climate change is changing the weather-dependent input parameters. In this context, it is a question of the parameters, which are incorporated into both the "Directives for the Standardisation of Road Surface Structures of Traffic Infrastructures" (RStO) and the calculational dimensioning (RDO Asphalt and RDO Concrete). Corresponding adjustment proposals for dimensioning (usually 30 years) will be formulated.
Checking standardised asphalt surfaces under changed boundary temperature conditions
Asphalt exhibits a strongly temperature-dependent elastic-plastic-viscous behavious with a tendency to form cracks in winter and permanent ruts in summer. The aim of this project is use the "Directive for the Calculational Dimensioning of Traffic Infrastructures with Asphalt Wearing Courses" to investigate the extent of the rise in mean annual temperature and impact of traffic, up to which the use of standard asphalt construction/dimensioning to achieve normal periods of use is possible. If, as a result, the periods of use become shorter, then material adaptation specifications have to be provided or alternative binding concepts developed.
Asphalt surfacing and extreme temperatures
With the introduction of the Directive for the Calculational Dimensioning of Asphalt Surfacing (RDO Asphalt), a procedure has been included for the first time in the set of regulations, with which the layer thickness of asphalt surfacing corresponding to individual stress situations (temperature and traffic loads) has been determined taking mechanical material properties as a basis. In the course of the dimensioning process, an optimisation of the structure ensues by means of layer thickness adjustment and/or a controlling of the material properties. At the present time, the latter variant neglects the thermophysical material properties of asphalt. It is intended to identify and examine the potential for optimisation possibly arising from adjusting the dimension process. By means of a targeted optimisation of the mix proportioning/mixing recipe with the aim of systematically changing the thermophysical material properties and hence thermal conditions occurring in the structure, a sustainable possibility to adjust the asphalt road structure was seen.
Effects of extreme weather on concrete roads
The aim of this project is to investigate possible effects of various climate scenarios on concrete roads in the federal trunk road network, and determine whether the periods of use normally set are reached. This investigation is intended to identify critical structures or endangered areas in the route network and undertake appropriate measures to reduce the vulnerability of the structures. The investigation is necessary since an unforeseen failure in the road structure, such as the sudden blow-up of the road surface, can result in a high-grade threat to road safety.
Effects of climate change on the operation of services
In order to be able to react to climate events expected in the future, these events must be known and the effects on the road maintenance services determined using climate scenarios. In the process, attention is to be paid to all services provided in accordance with the requirements specifications, such as snow clearing, de-icing, grass-mowing, wood and tree management, road surface cleaning, drainage systems cleaning and maintenance as well as storm damage clearance. Conversely, however, road traffic itself provides for a not insignificant contribution to climate change. Traffic congestion or traffic jams cause an increase in pollutant emission. In this regard, it is not known to what extent pollutant emission can be reduced by means of an increase in operational services. This project is expected to result in findings, which will provide the basis for a targeted development of road maintenance services with the aim of reducing the consequences and effects of climate change.