Mitigating impacts of roads on wildlife: an agenda for the conservation of priority European protected species in Great Britain

Abstract

Global increases in road networks have been matched by traffic flows and are implicated in declines of many sensitive species. Impacts on wildlife by linear development features such as roads include mortality due to vehicle collisions and secondary effects such as preventing traditional movements or severing links between populations. European legislation requires development activities to have ‘no detriment’ to the favourable conservation status of European protected species (EPS), including great crested newts (Triturus cristatus), hazel dormouse (Muscardinus avellanarius) and bats (Chiroptera). To protect these and other species, various mitigation measures are available. Within this review, we sought to identify best practice guidance for preventing and mitigating these impacts for EPS in Great Britain, evaluate the evidence underpinning these best practices and identity knowledge gaps that may impede progress in improving practices. Many current practices appear to be implemented at considerable cost despite limited evidence of their effectiveness. This is probably partly due to inadequate definition of effectiveness, which has most frequently been assessed as a reduction in absolute road mortality or increased frequency of safe road crossings. However, challenges in measuring benefits more appropriately, at spatial and temporal scales that are appropriate for population maintenance, may also have contributed. Evidence of the cost-effectiveness of mitigation works could underpin justification for the substantial investment required to implement many of the mitigation methods reviewed, could avoid the potentially wasteful use of ineffective methods and could better safeguard the conservation status of impacted EPS at local and national scales.