Traffic crashes of motor vehicles with ungulates (UVC) are a safety issue in many European countries where wild ungulates (e.g., roe deer, wild boar) live in large populations. Many preventive measures, in relation to safety of drivers, have been applied along primary roads. Fences, which aim at preventing ungulates from entering a road, are among the most widely used. Their construction and maintenance are, however, costly and time consuming. Overall costs are further increased when underpasses or even overpasses are built in order to secure landscape connectivity.
Secondary roads with lower traffic volumes and speed, than those usually measured on primary roads and motorways, are also places where UVC occur. Due to their extent and rather low benefit when compared to costs of fences accompanied by underpasses or overpasses, effective and affordable measures are needed for these roads.
Olfactory repellents (OR) are widely applied in many European countries in order to prevent UVC. OR are chemical substances, usually injected into a foam and placed on sticks installed with spacing of approximately 10 m along the riskiest road sections. The problem is that these measures have only rarely been reliably tested. Its effectiveness, in terms of roadkill (as well as traffic crash) reduction, have usually not been based on sound data and robust study designs.
Over the last five years, we studied OR effectiveness using two approaches: the change in the number of carcasses (Bíl et al., 2018) and changes in roe deer behaviour near roads (Bíl et al., 2020). Whereas the first study, based on the Before-After-Control-Impact approach, showed the UVC reduction between 26 – 43 %, the second approach, where we studied roe deer behaviour, indicated no clear effect of OR.
We began this year with a large-scale three-year study on Czech roads focused on OR effectiveness. During the first year, ungulate carcasses will be monitored at 133 places along the secondary roads (at both case and control sections). OR will be applied during the next year to case profiles only. Finally, the evaluation of the OR effectiveness will be evaluated. Together with this study, ungulate behaviour will be determined for several individuals equipped with GPS collars, at profiles where OR will be alternately applied. We also plan, as part of this study, to perform a cost benefit analysis related to OR costs and expected effectiveness.