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There is an urgent need for further development of new urban green infrastructure.

Most cities are growing rapidly and undergo densification processes, thus isolating remaining open spaces. Such urban greenways benefit residents by providing various regulating and cultural ecosystem services (e.g., experience of nature and improved health and wellness) and support biodiversity. To connect these isolated patches linear structures that function as corridors between them are important. Within these cities the provision of open spaces is limited and unevenly distributed, enhancing the need to provide green infrastructure. Urbanization is increasing worldwide with more and more people moving to expanding cities. As important elements of green infrastructure, set-aside railway bridges should be considered in future urban planning. As most animal dispersal was recorded during the night, railway bridges with no (or little) traffic during the night may also contribute to animal dispersal. Our findings indicate an important function of a set-aside railway bridges for connecting urban habitats. We found season- and daytime-dependent differences in the frequency the bridge was used. Many animals, however, were apparently dispersing, using the bridge to cross the busy road.

For some animals it is likely that the gravel bed, at least temporarily, serves as a habitat. We captured more than 1200 animals crossing the bridge: small mammals, reptiles and amphibians as well as numerous invertebrates including snails, woodlice, spiders, harvestmen, millipedes, carabids, rove beetles and ants. We installed drift fences with traps on a single-track, 32 m long and 6 m wide railway bridge with a simple gravel bed, and collected animals daily for 9 months.

We examined the function of a set-aside iron-steel railway bridge crossing a 12 m wide road with high traffic density in Basel (Switzerland) for dispersing animals. It is not known whether dispersing animals use railway bridges to cross roads. They are interrupted when railways cross major roads. As elements of green infrastructure, railway embankments are important corridors in urban environments connecting otherwise isolated habitat fragments.