The term Green Bridge has slightly different meanings depending on the policy area referred to, or stakeholders concerned. For example, within active travel groups Green Bridges can mean any crossing that allows pedestrians or cyclists to cross a road unimpeded. In the Scottish Green Infrastructure Forums view, a Green Bridge is a structure that is designed in a way that allows wildlife to cross a manmade impediment, such as a road or railway line; increase rain water retention; and reduce surface water flow when compared to the equivalent “grey bridge”. In some cases these benefits can be combined with active travel crossing points as long as this does not restrict the use of the bridge for wildlife.
Good examples of the types of infrastructure that SGIF consider as Green Bridges can be found here: http://ec.europa.eu/environment/nature/ecosystems/illustrations.htm
There are several examples of this kind of Green Bridge around the world, but very few in the UK.See some inspirational examples here: http://twistedsifter.com/2012/07/animal-bridges-around-the-world/. Natural England recently published an inverview of good examples of Green Bridges across the world which can be downloaded here
In Scotland, the Glasgow Clyde Valley Green Network are in the process of developing a Green Bridge crossing for the M73 at the Seven Lochs Wetland Park: http://www.centralscotlandgreennetwork.org/news-and-events/news/626-connecting-the-seven-lochs-wetland-park