Over- and underpasses for larger wildlife

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Background

Several over- and underpasses targeted particularly for larger wildlife has been built or are currently in construction in Sweden. These varies in design, for example dimensions, fencing/screening, and vegetation and other habitat components in and around passages. Some design parameters, most notably size, are highly cost driving, and better knowledge of design details is needed to make future constructions more cost-efficient.

There is generally a lack of rigid scientific support (also internationally) for the available construction guidelines, and there is an obvious risk that wildlife passages are built too small to fulfil their intended function, or conversely that they are built too large for precautionary reason. In either case, money may be wasted.

Monitoring of wildlife passages is largely neglected in Sweden and abroad, or conducted at a very basic level, not allowing to relate to set targets or making cost-efficiency comparisons. Furthermore, monitoring results from different passages cannot be easily compared or scientifically reported. Accordingly, opportunities to gain important knowledge are missed.

However, Trafikverket has now agreed on a standardized monitoring method, that allows the joint analysis of different passages that is necessary to produce new, scientifically founded construction guidelines.

Activities

In this subproject we will monitor wildlife’s use of a number of over- and underpasses, and compare performance depending on size and design, and to a degree on siting and landscape type/geographical region.

Monitoring method will be similar between passages to facilitate direct comparison. As far as possible, data should be gathered from (and in cooperation with) monitoring studies conducted within the respective investment project. 

Field methods should include studies of animal movements and behaviour near and through the crossing (for example photo traps, sand beds and snow tracking), following standardized methods. Effect sizes will be compared with the cost of each improvement type.

The results will be published scientifically. 

Output

This subproject produces values of the efficacy of wildlife over- and underpasses in connecting wildlife between roadsides. Efficacy is separated between species and categories of animals (age and gender) to put light on population level impacts. The most important outcome is that the results enables cost-efficiency comparisons between different crossing types and designs, and ideally (together with previous subprojects) to point out the optimal design for a standard design for wildlife passages.

Study objects/sites

Data collection (photo trapping) is ongoing in and around the following bridges: 

  • Large moose underpass at national road 31 near Tenhult
  • Four minor passages at national road 31 near Tenhult
  • Red deer underpass at national road 11 near Vomb 
  • Moose bridge at national road 73 Älby, Nynäshamn
  • Reindeer bridge over Haparandabanan railway at Sangijärvi
  • Three minor bridges at Haparandabanan railway between Kalix and Haparanda
  • Reindeer bridge over road E10 at Mertainen
  • Ecoduct and cattle tunnel at E20 at Sandsjöbacka

The following existing bridges and tunnels are candidates for study objects (the list is not exhaustive):

  • Four combined fauna/road overpasses at national road 45 between Kungälv and Trollhättan (*Mats Lindqvist)
  • Reindeer bridge over Malmbanan railway at Råtsi (*Katarina Andersson/Malin Delvenne)
  • Reindeer bridge over railway at Aitik mine (*Katarina Andersson/Malin Delvenne)
  • Longer road tunnels, for example at E18 (Ullbro, Frösvi), E20 (Jeriko), road 265 (Löttinge).

New wildlife passages constructed during the project period are also candidate study objects, for example:

  • Fauna overpass and bridge over stream at E20 Hova
  • Fauna underpass under E6 at Hallandsås
  • Red deer bridge over motorway E65 at Lemmeströtorp 
  • Fauna bridge over national road 21 at Ekeberg (between Kristianstad and Hässleholm)
  • Fauna passage at road E22 Norra Binga (east Blekinge)
  • Two fauna underpasses at road E20 Kristineholm-Bälinge
  • Fauna passage at intersection at E20 Tollered-Ingared
  • Smaller fauna passage under national road 23/34 at Hamra (Åtvidaberg)
Photo © PEAB Air