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About the project


Roads may have a negative impact on bat populations. Roads induce increased mortality rates in the populations due to collisions with road traffic. Roads may also impact bats indirectly by acting as barriers in the landscape or by reducing habitat suitability through noise and lighting pollution.Some bat species fly relatively close to the ground, forest edges or hedgerows, and may attempt to cross roads at low altitudes and experience a high collision risk. Bridges, elevated road stretches and roads near roosting sites may also pose a risk to other bat species which normally commute and hunt at higher altitudes.

There are more than 50 bat species in Europe. Generally, all bats are protected by national legislation and international treaties (Bern and Bonn Conventions and the EUROBATS Agreement). Within the European Union all bat species are strictly protected by the Habitats Directive, according to which the construction of transport infrastructures must not have detrimental effects on the conservation status of strictly protected species. Therefore, effective mitigation and compensation strategies for bats are needed when expanding or upgrading road infrastructures. As all bat species have a relatively low reproductive rate, long life expectancy and show high site fidelity, their population status is very sensitive to increased mortality rates and habitat changes.

A range of measures has been employed to mitigate and compensate for the potential negative effects of roads on bat populations, e.g. gantries, hop-overs, green bridges, viaducts, culvert underpasses, adapted road bridges and technical structures, but the evidence of these measures' effectiveness is limited.

Many descriptive studies have just recorded bats' use of the measures but not the effectiveness, and often the studies have not paid sufficient consideration to differences between species and the large plasticity in the bats' behaviour. In the latest years some outstanding studies have been made on the British Isles, but there is still an urgent need to document the effectiveness of different bat mitigation strategies.

The Conference of European Directors of Roads (CEDR) has commissioned this project to evaluate bat mitigating strategies on roads in Europe and the evidence of effectiveness of the mitigation and compensation measures. The results of the project will benefit road and nature agencies and managers, bat researchers and consultants by provide better evidence for decision making on cost-effective methods to reduce the impact by roads on bats and improve the conservation status of bats.


The project aims to elucidate the status and effectiveness of bat mitigation on roads by:

  • identifying mitigating measures for bats constructed at roads across Europe,
  • reviewing literature on the effectiveness of bat mitigation measures,
  • evaluating the effectiveness of hop-overs for bats,
  • identifying future research needs on bat mitigation on roads,
  • providing up-dated guidelines for authorities, consultants and developers.