Transport networks divide natural habitats into small isolated patches and create barriers between the remaining patches. This can have two primary effects on species; firstly, it can reduce the size of habitat patches so much that they can no longer support viable populations of important species; and secondly, it can result in the remaining patches being so isolated from each other that individuals have a low chance of moving between patches. Being unable to move between patches renders species vulnerable to local and regional extinction. Through these processes, habitat fragmentation by transport networks and consequential secondary developments have become one of the most serious global threats to biological diversity.

Although human activity started to fragment nature many centuries ago, the rapid increase in density of transport networks during the 1900s and the effect of increased accessibility have greatly accelerated this impact