Transport infrastructure has a wide array of effects on terrestrial and aquatic ecosystems, and road and railway networks are increasingly being associated with a loss of biodiversity worldwide. Environmental Impact Assessment (EIA) and Strategic Environmental Assessment (SEA) are two legal frameworks that concern physical planning, with the potential to identify, predict, mitigate and/or compensate transport infrastructure effects with negative impacts on biodiversity. The aim of this study was to review the treatment of ecological impacts in environmental assessment of transport infrastructure plans and projects. A literature review on the topic of EIA, SEA, biodiversity and transport infrastructure was conducted, and 17 problem categories on the treatment of biodiversity were formulated by means of a content analysis. A review of environmental impact statements and environmental reports (EIS/ER) produced between 2005 and 2013 in Sweden and the UK was then conducted using the list of problems as a checklist The results show that the treatment of ecological impacts has improved substantially over the years, but that some impacts remain problematic; the treatment of fragmentation, the absence of quantitative analysis and that the impact assessment study area was in general delimited without consideration for the scales of ecological processes. Actions to improve the treatment of ecological impacts could include improved guidelines for spatial and temporal delimitation, and the establishment of a quantitative framework including tools, methods and threshold values. Additionally, capacity building and further method development of EIA and SEA friendly spatial ecological models can aid in clarifying the costs as well as the benefits in development/biodiversity tradeoffs.

Transportation infrastructure has a wide range of effects on ecological processes, which result in both positive and negative impacts for biodiversity. However, the treatment of biodiversity in planning and environmental assessment have been criticized, especially regarding habitat loss and fragmentation effects, the low use of quantitative methods and that of assessments being descriptive rather than analytical and predictive. The aim of this study was to assess the impacts of the Swedish road network by spatial modelling of road effects, to explore potential impacts of fragmentation and disturbance effects of roads on habitat networks for selected ecological profiles, and to discuss the utility of applying quantitative methods for environmental assessment purposes. Habitat and landcover data was used for creating habitat networks for six ecological profiles. Fragmentation and disturbance effects were modelled in GIS and FRAGSTATS was used to quantify ecologically important landscape metrics on habitat amount and connectivity. The results showed that natural grasslands and southern broadleaved forest were substantially more exposed to road effects in Sweden, compared to old coniferous and trivial broadleaved forest. Furthermore, habitat loss was a main consequence of road effects, and forest species with high area demands were most prone to be adversely impacted. Suggestions on method development in order to increase the quality of the analysis methods for environmental assessment are discussed. The potential is seen as high for use of quantitative ecological methods to generate baseline environmental information as well as coarse predictions on likely consequences of development options, useful for environmental assessment.

Transport infrastructure is closely linked to several sustainability issues of main policy relevance, and significant impacts on biodiversity as well as resource use and construction costs relate to the corridor design and location in the landscape. The aim of this study was to develop methods for railway corridor planning, in which corridor design and location would be based on important ecological and geological sustainability criteria. The method, an MCA framework including both spatial and non-spatial MCA, was demonstrated on a railway planning proposition in an urbanising area north of Stockholm, Sweden. Alternative spatial alignments for 6 railway corridors were derived based on criteria representing biodiversity, resource efficiency and costs, developed from ecological and geological knowledge, data and models. The method identified a study area specific positive synergy between ecological and geological sustainability criteria. The evaluation part of the methodology could furthermore identify uncertainties in the input data and assumptions and conflicts between ecological criteria. In order to arrive at a well-informed decision support system, the criteria as well as the decision rules employed could be further elaborated. Other relevant sustainability issues would also need to be integrated, such as cultural landscapes, recreation, and other ecosystem services. Still, arriving at a corridor design informed by the ecological and geological conditions in the planned area, as demonstrated by this study, could improve the sustainability performance of transport infrastructure planning.

Transport infrastructure can impose significant barriers to movements to many, if not most terrestrial animals. Barrier effects can lead to increased isolation of wildlife populations, which in turn might have demographic effects and even increase genetic differentiation between neighbouring populations. This study attempted to clarify the role of fauna passages and generic landscape patterns for connectivity in fragmented landscapes, and to improve the theoretical basis for future experimental approaches to evaluate the effectiveness of barrier mitigation strategies. Specifically, the issue of whether it would be more effective to construct a single large rather than several small crossing structures (SLOSS) was addressed by this study. Three hypotheses were formulated on the relationship between habitat connectivity, as a prerequisite for genetic exchange, and habitat aggregation and contrast between habitat types. Random landscapes with different combinations of aggregation, contrast and number and size of fauna passages were created in a GIS. Connectivity was then quantified as a function of movement resistance using circuit theory and related methods, and measurements from the random landscapes were statistically analysed. The results indicate that in any landscape, it would be more effective to construct several small fauna passages instead of a single large one to mitigate the effect of a barrier. The level of aggregation appeared to have no influence per se on connectivity, and increasing the level of contrast increased the variance in the results. Results indicate that the effectiveness of a fauna passage will to a large extent rely on the location of a fauna passage relative to how the mitigation target species perceive the landscape in terms of contrast between different habitat types. A predefined interval between fauna passages could therefore result in highly ineffective mitigation, in a situation where a fauna passage would be located in habitat perceived as of high resistance. It is recommended that barrier effect mitigation strategies focus on the location and design of several small fauna passages rather than a single large one. Future research should focus on the development of dispersal and movement models for a set focal species that perceive a minimum degree of contrast between habitat types.