Madrid is building a new wildlife overpass, covered in soil and plants, that will span the M-607 so that animals can cross the road without risking their lives. It will have no cars or asphalt, only holm oaks, broom, rosemary, and Mediterranean scrub, and will be one of the most spectacular wildlife crossings in the region, designed for wild boars, roe deer, fallow deer, and other species that move between Tres Cantos and Colmenar Viejo.
The new wildlife crossing is part of the construction of the third lane of the M-607 between these two towns north of Madrid, a project that has been underway since 2024 and which, at the environmental authority’s request, incorporates this elevated ecological corridor as a condition for expanding the road’s capacity. The highway carries heavy traffic and crosses an area of high natural value, which results in a constant risk of wildlife being struck by vehicles. The goal of the wildlife bridge is to reconnect the territory that the highway split in two and provide a safe passage that animals recognize as part of their natural route.
An overpass so wildlife can cross safely
The structure, which will be built in the municipality of Colmenar Viejo, at approximately kilometer marker 0.4 in the direction of Madrid and 7.04 in the direction of Colmenar, will be a true giant: 137 meters long and 56 meters wide, supported by four concrete false tunnels that will cover the M-607’s roadways and service roads. Unlike conventional bridges, the deck will not be paved. About two meters of topsoil will be spread over it, enough to create living ground where plants can take root and which, to the eyes of a wild boar or a roe deer, will appear as just another hill, not an artificial structure.
The “green highway” will not be a simple mound of earth. The project includes a detailed landscaping of the crossing: planting broom, rose hips, rosemary, and other native shrubs, as well as holm oaks on both sides of the wildlife crossing to hide traffic from the animals’ view and reduce noise and glare. This vegetative screen will be complemented by a two-meter-high wooden fence, which will guide wildlife toward the bridge and prevent it from approaching the edge of the roadway. At the ends, large stone blocks—weighing between 400 and 800 kilograms—will block vehicle access but provide shelter and resting spots for crossing animals.
These types of overpasses, common in Central European countries, are also becoming more widespread in Spain as a key tool to prevent wildlife collisions—one of the most frequent types of accidents on roads that traverse forested areas. In the case of the M-607, the wildlife crossing complements other existing crossings along the route, such as the one on the M-501, but at a particularly sensitive point due to the density of wildlife and the planned increase in lanes with the new project. The idea is that, once operational, it will become the preferred corridor for the movement of wild boars, roe deer, and fallow deer—which are abundant in the area—thereby reducing the number of wildlife crossings onto the roadway and, consequently, the number of accidents.
There is still no exact date for the start of construction on the wildlife crossing, but the Community of Madrid has included it in the overall schedule for the third lane project, which has already completed its first two kilometers and will continue through next year.