Green Bridges and Green Tunnels

Green bridges, also known as landscape bridges or wildlife overpasses, allow birds, mammals and insects to keep moving despite a railway or road in their path. At ABG we have developed geosynthetic systems that allow green bridges to attenuate storm water as part of a site wide SuDS plan, while providing protection to waterproofing and preventing the build up of hydrostatic pressure on the structure.

Green Bridges

The report  "Green Bridges - A Literature Review (NECR181)" was commissioned by Natural England and is the first worldwide study of green bridges. It identified that green bridges can make an important contribution to sustainability by:

  • Creating a safe crossing point for wildlife
  • Joining up habitats and connecting colonies
  • Providing a home for wildlife
  • Creating a crossing point for people 
  • Facilitating movement of beneficial pollinators
  • Integrating roads and railways into the surrounding landscape
Green bridge on a moorway highway project

A green bridge can significantly reduce the environmental impact of linear assets such as highways and railways through sensitive design by addressing the severance effect.

ABG's green bridge technology provides structural drainage and physical protection to the structure, and also allows attenuation of rain water to mitigate the effects of storm events. The ABG system is significantly more lightweight than traditional solutions which minimises the dead load loading, and stores water to sustain trees and vegetation during dry periods. Our geosynthetic systems can be applied both to new build and retrofit schemes.

Green Tunnels

Green tunnels, also commonly known as cut and cover tunnels, provide similar environmental benefits to green bridges but over longer stretches.

Cut and cover tunnelling is one of the oldest tunnel construction methods. At a basic level the tunnel is constructed by excavating to the required level, constructing the tunnel and then covering it. 

Cavidrain  drainage  composites  are  used  in  Tunnel  cut  and  cover  projects

ABG Deckdrain geocomposite drainage is used to enhannce and protect the waterproofing and provide drainage for the structure, which removes the need for bulky porous blocks and the logistical challenge of importing granular fill.

The cover over the tunnel becomes "green" when it is designed from an ecological perspective, and to minimise the impact of the structure on the surrounding environment. Part of that design consideration should be the movement of materials during the construction phase which can create a significant carbon cost. Using ABG Deckdrain has been shown to offer a carbon saving of more than 90% when compared to traditional methods.

ABG Cavidrain Invert geocomposite tunnel drainage

Green bridges and green tunnels allow us to integrate our expertise in green infrastructure with our long established background in civil engineering. 

Structural Drainage of Green Bridges and Tunnels

As part of the design of both green bridges and cut and cover or green tunnels, the external surfaces of the structure should be waterproofed and a drainage system required to relieve pore water pressure on the crown of the structure.

Structural drainage for an arched green bridge and tunnel project

A cost effective and quick installation without the need for specialist handling equipment, without overloading the structure or damaging the waterproofing membrane during construction, would be an installation of a drainage geosynthetic. ABG Deckdrain drainage geocomposite is an alternative to the more expensive porous block drainage systems.

Arch tunnel concrete structure units ready to receive waterproofing and Deckdrain drainage/protection geocomposite layers

Click to open some examples where ABG geosynthetics have been used to provide highway and rail green bridges and green tunnel drainage solutions:

Click for more information on our geosynthetic systems for Tunnels, Railways and Highways


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