Climate proofed standards for road design, construction and maintenance

Road transport is essential for the economy and society worldwide. In 2017, road transport in the EU28 accounted for 73.3% of the total volume of land freight transport and 80.1% of passenger transport. In order to ensure uninterrupted availability of the road network, measures need to be taken to increase the resilience of road transport infrastructure to weather extremes and climate change, which should address, in parallel and in synergy, the other challenges road transport is facing, such as its gradual growth and the decrease of carbon intensity of transport in line with the carbon-neutral strategy.

An effective way to increase the resilience of road transport is to identify, develop or revise and subsequently implement construction and design standards. These activities should be incorporated into a standardized and well-described process aiming at increasing the overall resilience of the road network. The adaptation framework for road infrastructure has been described and piloted by the ROADAPT (Roads for today, adapted for tomorrow) project. The adaptation framework is also addressed in the PIARC report (2015), which defines four main stages:

1. Identifying scope, variables, risks and data with the focus on climate change scenarios for the given territory and exposure and sensitivity analysis of road assets to climate change.
2. Assessing and prioritizing risks. This stage includes vulnerability analysis carried out to identify critical elements of road infrastructure.
3. Developing and selecting adaptation responses and strategies. This stage outlines the identification, selection and prioritization of adaptation responses identified within stages 1 and 2.
4. Integrating results into decision making processes. Namely, the results of the stages 1-3 should be effectively incorporated into asset management plants, investment plans, traffic management strategies and other strategic documents and standards.

Road transport assets requiring revised proofed standards can be grouped into the following categories.

Road pavement

The main risks to the road surface associated with climate change are, depending on the climate zone, extreme heat and insolation, higher occurrence of heavy rain and temperature fluctuation around the freezing point.

Very high temperatures are manifested by an increased risk of asphalt rutting, flushing and bleeding of bituminous surfaces and/or cracking. As the temperature of the asphalt mixture increases, the binder phase loses stiffness and the irreversible deformations caused by static or dynamic traffic loading will accumulate at a faster rate. Possible solutions include following ones:

• Adjustment of bituminous mixture design (using of binders with higher softening point, including polymer modification of bitumen, selection of stronger aggregate skeleton);
• Adjustment of structural design of the pavement (flexible, semi-rigid and rigid/composite designs);
• Greater use of concrete due to its higher temperature resistance and other advantages (longer lifetime, possibility of increased load, lower need for maintenance) albeit slightly higher purchase costs.
• Changing the design of the concrete pavement mixture to reduce the amount of water required.
• Increase the reflectance (albedo) of the road surface e.g. by means of using bright, coloured elements on the road or reflective coatings of road surfaces.
• Cooling pavements with water.

The primary impacts of an increase in frequency in intense precipitation include water damage to asphalt, reduced bearing capacity of lower pavement layers and reduced safety and comfort for the user (less friction, less comfort). Possible adaptation responses, similar to those coping with temperature fluctuation and higher frequency of freeze/thaw cycles are:

• Use of permeable/reservoir pavements. Water is stored in the pavement structure and infiltrated into the soil or discharged by a drainage system.
• Use of porous top layers that can facilitate the drainage of the water to the sides of the road and prevent aquaplaning.
• For concrete surfaces higher cement contents and lower water cement ratios are recommended.
• Development of hydrophobic coatings suitable for use at the micro-mechanical and or pavement surfacing level.

Road drainage systems

Drainage system capacity should be adapted to higher intensity and frequency of extreme rainfall events and complemented with water retaining facilities (e.g. dams, reservoirs) and structural protection measures (dikes, embankments). The design for culverts should be adjusted to accommodate higher water volumes within a short period of time. In terms of defining the capacity design of the drainage system, the intensity-duration-frequency curves (IDF curves) should be used, taking into account the influence of climate change and updating these IDF curves with the rainfall characteristics projected in future climate scenarios.

Bridges and similar infrastructure

The main climate change concerns relevant to design, construction and management of existing bridge structures are higher occurrence of flooding, higher river discharge, erosion and slope instabilities and temperature fluctuation. The standards for bridge structures which are currently used show considerable resistance to these effects; nevertheless, the research of new climate-proofed standards is ongoing.

Vegetation along roads

Vegetation along roads contributes to environment protection, in particular reducing noise and pollution, and can also have an adaptation function, for example protecting road from direct sunlight. On the other hand, improper use of vegetation along road can be a risk factor of traffic disruption when extreme weather events occur and may also influence road safety. The recommendations towards building up climate resilient roads therefore include replacement of mature trees with hedges (using elastic woody plants suitable for and more adapted to a given climate zone) and planting the vegetation at a sufficient distance from the road.

Climate change will also affect road maintenance, which therefore must be taken in into account when dealing with climate-resilient road infrastructure. Attention shall be paid to all maintenance services, like cleaning and maintenance of drainage systems, removing of storm damage, cleaning of roads, pruning of brushes and snow and ice removal. The efficiency of adaptation measures and maintenance planning can be suitably complemented with traffic telematics elements, in particular online cameras, weather stations, road load sensors, and advanced telematics systems which are able to regulate traffic flow and prevent traffic congestion.

IPCC categories

Structural and physical: Engineering and built environment options, Structural and physical: Technological options

Stakeholder participation

The identification, development and implementation of climate-proofed standards for road transport infrastructure require the involvement of a wide range of stakeholders. The process is normally triggered and coordinated by the administrations and/or agencies responsible for road transport management. These subjects are scientifically supported by research institutions working in the field of sustainable development transport, as for example FEHRL (Forum of European National Highway Research Laboratories), as well as by research institutes specialized in climate research, which provides input data for risk and vulnerability assessment. Once identified, the new construction standards are implemented by construction companies working in the field of engineering constructions.

Success and Limiting Factors

As the implementation of new or revised standards takes place mainly within reconstruction of existing or construction of new infrastructure, the effectiveness of adaptation responses is dependent on road infrastructure development plans. Other important success factors are the availability and quality of detailed background knowledge on climate change risk and vulnerability of the road network in a given area and sufficient institutional, financial and human resources.

The construction of new roads or the adaptation of existing ones according to new climate proofed standards can be in conflict with territorial development plans (e.g. for housing), other sectoral strategies or environmental protection objectives. Identification and resolution of potential conflicts is therefore needed in the initial phase of the road design and construction.

Costs and Benefits

Costs depend on the size of the area of interest, the length of the road network the adaptation intervention is dealing with, the level of climate change risks the road transport infrastructure is facing and the specific typologies of adaptation measures considered. Financing resources are normally provided by road authorities; they might be co-funded from public budgets aimed at climate change adaptation and infrastructure development with possible use of European financial instruments.

Main benefits are expected to be related to ensuring connectivity and operation of the road transport network also in case of extreme weather events and in changed climatic conditions, with positive implications for economic prosperity, safety and welfare. Moreover, long-term savings in operating and maintenance costs of transport infrastructure are expected.

Legal Aspects

The main strategic document of the EU relevant for the climate change adaptation of transport is the White Paper on Transport “Roadmap to a single European transport area – towards a competitive and resource-efficient transport system”. One of the objectives of this strategy is to ensure, that the EU-funded transport infrastructure takes into account energy efficiency needs and climate change challenges (climate resilience of the overall infrastructure), At the national level, the development of road transport, its sustainability and adaptation to climate change are addressed by national transport strategies, and in some cases by national climate change adaptation plans setting out the priorities and measures for each sector. Design and operation technical standards for road transport infrastructure are set out by national legislation.

Implementation Time

The time needed for the implementation of a full revision of climate-proofed standards for road infrastructure can vary between 1-3 years, depending on the country and the scope. The on-site implementation can take from months to several years, according to the size and the level of complexity of the construction works.

Life Time

The revised standards applied to the construction of new road infrastructure and the upgrading and maintenance of existing one normally have a life spans ranging between 25 and 100 years. The lifetime of the road infrastructure is several decades depending on the level of maintenance and operating conditions (e.g. traffic load, natural conditions, etc.).

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