Workshop Minimizing road effects through the bundling of infrastructures: Current state of practice guidelines and research needs

One of the most fundamental measures to minimize the detrimental effects from transport infrastructures on nature and wildlife is considerate siting. The siting of a road or a railroad often determines both the magnitude and character of the final effects, and sets the stage for all further mitigation and remedial efforts. New infrastructures should be avoided in the most valuable or sensitive habitats and landscapes, and fitted into the existing infrastructure network to cause a minimal increase in the total impact.

A measure assumed to keep the effects of the road network at a minimum is to bundle infrastructures, i.e. to locate them close together. Bundling has the goal to keep as large areas as possible free from roads and traffic, and it also creates synergies in the construction of technical mitigation structures such as wildlife passages, fencing, and audio-visual screening. It may, however, be argued that bundling results in stronger barriers and higher disturbances that are above critical thresholds, and if these impacts are not well mitigated the end-result may be worse than if the impacts were distributed more evenly among several roads across the landscape. Moreover, interaction between bundled infrastructures may bring about special circumstances for wildlife mitigation, such as complex road crossings and fencing, and isolation of habitat strips.

The bundling of transport infrastructure is a planning principle in several countries in Europe, but it is not clear to what extent this principle actually affects decisions about road siting. Previous modelling results suggest that, in most cases, concentrating traffic onto fewer infrastructure corridors minimizes the overall isolation and mortality effects. Yet, the potential importance of bundling of transport infrastructures has generally received little attention in research. Therefore, we currently have rather weak evidence for guiding decisions in the planning of road networks to reduce impacts on wildlife in real landscapes. Road ecology needs further development of network theory and underpinning by empirical studies. There may also be a need for development of technical mitigation structures that can handle bundled infrastructures, and their effectiveness needs to be monitored.

This workshop will highlight the pros and cons of infrastructure bundling, in the light of network theory, technical limitations, and the importance of creating functional movement corridors for wildlife. We aim at reviewing the current state of practice in selected European countries, leading to a cross-country comparison. Theoretical and practical examples are presented that will provide a foundation for a discussion among workshop participants of the research needs and guidelines for planning at the scale of road networks.

Bundling, Cross-country comparison, Movement corridors, Network theory, Workshop