Roads and traffic affect amphibian populations in four ways: they decrease habitat surface and quality, enhance mortality due to collisions with vehicles, prevent access to resources and habitats on the other side of the road, and subdivide animal populations into smaller and more vulnerable fractions. Amphibians are the most frequently road-killed group, with casualty rates of 60–90% in vertebrate road ecology studies.
Permanent amphibian road mitigation measures consist of 3 basic technical solutions – amphibian underpasses crossing the main road, guiding fence along both sides of road and grid covered tunnels on junctions with less intense traffic. Soultions will be defined in detail in project documentation for each road section, following some general guidelines.
Existing international guidelines prefer rectangular tunnels, where adequate width of the tunnel is important, too. The recommended cross-section dimensions for up to 20 m long rectangular tunnels measure 1 x 0,75 m. Distance between neighbouring tunnels is as well very important and depends of specific target species; for Italian crested newt should not exceed more than 30-50 m.
For the tunnels to be fully functional and effective, guiding fences along the road are needed as they are directing the animals towards tunnel entrances and provide a barrier to the road. Fences will be placed close to the road to minimize the length of the tunnel. The ends of the fences should be U-shaped to turn the animals back in direction to the tunnel. Upper edge of the fence should be curved to prevent animals from climbing over.
Accordingly amphibian tunnels and permanent fences will be installed on 4 (out of 13) most problematic longer road sections identified in Slovenia, all in Natura 2000 sites, for which project documentation will be prepared in A.2:
Road R3-647, section 1368 Mlačevo–Rašica on Radensko polje
Road R3-642, section 1146 Vrhnika–Podpeč in Bistra on Ljubljansko barje
Road R3-642, section 1146 Vrhnika–Podpeč near Pako-Goričica on Ljubljansko barje
Road R3-642, section 1147 Podpeč–Ig between Jezero and Podkraj Ljubljansko barje
Final project documentation from A.2 will serve as baseline for public tender on which the contractors for project executions will be selected.
To avoid disturbing amphibians during migrations all construction works will be executed during non-breeding period of amphibians. The construction will be supervised by construction engineer accountable for adequate project execution, as well as CKFF, who will be supervising amphibian functionality of the executed measures.
After the installation of tunnels and fences, maintenance plans will be prepared by DRSI, as responsible public body, who will ensure that the plan will be part of the concessionaire agreement for the road maintenance for each road sections in years to come.