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Adaptation option

Floating or elevated roads

Road transport infrastructure prone to flooding needs to be flood proofed to reduce the potential negative impacts of these events on transport routes and ensure connectivity of the road network, accessibility to or - if necessary - evacuation from flooded areas. Available options to reduce the negative impacts of flooding include use of appropriate design and materials, structural protection measures (flood protection barriers) and regular careful maintenance. The construction of floating and elevated roads represents an alternative option, which also provides additional benefits other than climate-proofing of road transportation. 

Floating roads are roads that float on water or are built on a very unstable substrate, like peat. These roads can represent both temporary and permanent solution in areas where standard roads are difficult or even impossible to build due to unfavourable natural conditions. Floating roads were for example used in Scotland to make windfarm areas lying on peat bog accessible. They can be used in permanently or intermittently flooded areas or in areas particularly prone to flooding, thus playing a role in disaster risk management and climate change adaptation. Floating roads are more flexible than bridges and can also be used as a bypass in case of road blockages due to reasons other than flooding, e.g. due to roadwork on a bridge or on a road along a waterway. This measure can be quickly assembled and easily relocated. Moreover, floating roads take less space than traditional alternatives. Technically, floating roads build on water are placed on floating pontoons, so they can move accordingly to the change in the water level. On unstable solid substrate, two layers of geogrid are used as structural elements of the road.  

Contrary to floating roads, elevated or flyover roads are normally used in the road network. Due to their designed elevation they can ensure connection to the wider road network also in case of flooding events. Elevated roads can look like a fixed bridge, but they are usually longer and rise above the ground for their entire length. Elevated roads can also be constructed for other reasons than flood protection: optimization of the traffic flow (e.g. in urban areas, to avoid too many road crossings), construction on hilly terrain impeding ground level roads or minimization of direct environmental impacts on precious ecosystems (although elevated roads can still significantly alter the local landscape). An elevated road can also be constructed on top of an embankment; in this case it is also called a causeway. For example, Afsluitdijk is a 30 kilometres long dike and causeway heading across a large bay in the northwest of the Netherlands. The dike is equipped with shipping locks and sluices to enable discharge of water between the Inselmeer and the sea and make the water route navigable. The construction of elevated roads is usually more expensive than that of ground level road infrastructure. However, the increased transport resilience to climate change is usually an added value and not the main purpose for their construction. 

Additional Details
Reference information

Adaptation Details

IPCC categories

Structural and physical: Engineering and built environment options

Stakeholder participation

The main actors involved in the design, construction and maintenance of floating or elevated roads are similar to those involved in the development of other road transport infrastructure. They include territorial planners and urban developers, national or subnational administration bodies responsible for road network, and construction companies and institutions and organisations in charge of environmental protection. The involvement of research institutions is also highly important both on technological aspects and to deal with climate change vulnerability and risk analyses. Citizens and users of the transport infrastructures must be correctly informed on the location of floating and elevated roads and their use in case of flooding or any other emergency event. 

Success and Limiting Factors

Funding availability, support of administration bodies in charge of transport infrastructure and involvement of stakeholders including transport and environment experts in the process of designing and constructing elevated or floating roads are some of the major success factors. 

Major limiting factors are related to conflicts with other land uses (agricultural, residential and recreational uses), mismatch with regional transportation strategies and insufficient financial resources to ensure the proper maintenance of the road infrastructure after the construction. As for any other road infrastructure, environmental impacts (e.g. noise and air pollution, destruction or fragmentation of habitats, etc.) during construction and operation phases and related mitigation measures must be carefully taken in consideration in the assessment of the alternatives. Impacts on ecosystems can be lower than those due to ground level roads, while elevated roads can more significantly affect the integrity of the landscape.  

Costs and Benefits

Floating roads are less expensive than bridges, while elevated roads on top of an embankment are generally cheaper than constructing a bridge-like road. After construction, both floating and elevated roads do not need more maintenance than any other road. 

Elevated roads are effective against storm water runoff related flooding because they are normally situated higher than water levels. Floating roads and related accessing ramps can adjust to the fluctuating water level. In case of floods, the most important benefits of these infrastructures include: ensuring the accessibility to the area for rescue services, making the connection to the overall road network climate proof and therefore preserving the mobility of inhabitants, enabling the evacuation from the area when needed and necessary. Elevated roads in the urban areas also serve for redirecting the traffic beyond densely populated areas and therefore help in keeping cyclists and pedestrians safe on roads. 

Local, regional and national authorities are responsible for the realization and management of floating and elevated roads. The legal aspects related to the design, building and maintenance of elevated and floating roads are very similar to those of standard road transport infrastructure. 

Implementation Time

The preparatory phase for the construction of floating or elevated roads includes several expert analyses (including a cost-benefit evaluation), designing and dimensioning, administrative processes including environmental impact assessment and evaluation focused on climate change proofing. This phase lasts approximately 1-2 years. The construction phase duration varies between several months to several years depending on the scope, size and complexity of the construction. 

Life Time

If up to date technologies are used in construction and the proper and regular maintenance of the infrastructure is ensured, the lifetime of elevated and floating roads is in the order of decades. However, over time there might be a need to rebuild or adapt the roads to better cope with changing transportation needs or climate change.  

Reference information


Forestry Civil Engineering, Scottish Natural Heritage (2010). Floating roads on peat.  

Published in Climate-ADAPT Jun 07 2016   -   Last Modified in Climate-ADAPT Aug 17 2023

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