Ecoduct over the A1 motorway, Kootwijk

Infrastructure, and especially road traffic, counts as one of the chief causes of the segmentation of wildlife habitats. The survival of entire populations is threatened by the barrier effect of motorways. The genetic diversity of wildlife species is in danger: isolation of too small a population leads to inbreeding within the group.

A number of European countries have taken the initiative to counteract this segmentation. In the Netherlands this intention has been formulated in a government policy known as the Ecologische Hoofdstructuur (‘National Ecological Network’).

The first concrete measures were taken in the forests of the Veluwe, where the A1 motorway cuts through the Hoge Veluwe national park. The plan for an ‘ecoduct’ near Kootwijk arose in order to counteract the barrier effect of this motorway. The ecoduct is meant to stimulate the exchange of genetic material between wildlife populations rather than to make busy animal routes safe.

The use of the ecoduct by red deer was used as a guideline for the design. The plan of the ecoduct has the form of an hourglass and works like a trap (though not for entrapment). At the edge of the forest the ecoduct is about 80 metres wide, while in the middle of the span it is 30 metres wide. In order to limit the traffic nuisance for the animals and in order to make the crossing-point seem as natural as possible the bridge deck is lined by an earthen wall measuring 1.50 metres high which is planted with trees and shrubs.

The walls of the ecoduct are made from terre armé, roughly translated as ‘reinforced earth’, which is a technique that involves stacking up a wall of prefab concrete elements that are anchored in the earthen wall behind. The span of the ecoduct is made from concrete cast on site, with a 1.50-metre layer of soil on top for grass and shrubs to grow.