When motorways are constructed, the barrier effect may be so great that no further exchange of genes between populations on either side of the road takes place. This may result in a very small gene-variation, which in turn could threaten survival of the species in a given area. For some species the extinction of a given population can have major consequences, and it is therefore important to ensure that it is possible to cross the road.

Different guidelines of how to achieve this exist in different countries. This report examines the guidelines from Denmark, Austria and California. However, it is difficult to apply the lessons learned from other countries in Denmark, because nature reserves in Denmark are more affected by humans, and many natural habitats are highly fragmented.

This report takes the motorway between Ikast and Låsby as its starting point. Here, the fauna passages are investigated. From these studies, the quality of the fauna passages, the location of them and the need for placement of additional fauna passages are all analyzed. On the basis of both these analyses and relevant literature, new recommendations are given.

Although it is possible to detect an improvement in the development of fauna passages along the new route compared to older stretches, it is clear that there is still a lack of knowledge in order to place the fauna passages as optimal as possible. In this connection, behavioral studies of the different species in relation to motorways are of particular interest, yet still lacking.