6.1.1. Goals of monitoring and evaluation

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Last update: June 2023

Monitoring must be a continuous process interspersed with evaluation events defined during the design phase and applied during construction and operation to enable adaptive management of the infrastructure and the mitigation measures. Some specific monitoring activities provide information to evaluation for determining the effectiveness, or ineffectiveness, of mitigation actions. Other monitoring activities need to be maintained for the long-term because of changes in traffic, infrastructure and landscape conditions. Such variations increase due to climate and land use change and must be assessed to undertake corrective actions or adaptation of the infrastructure to increase its resilience and mitigate any new impacts in biodiversity.

Identifying the real impact of transport infrastructure on target species, habitats and ecosystems is therefore one of the main goals of monitoring and evaluation. This means, all negative impacts such as habitat loss and fragmentation, fauna traffic mortality, disturbance, pollution or the spreading of invasive alien species could be subject to monitoring and evaluation on long term period (even more than 10 years), as long as these impacts remain significant according to recurrent evaluation.

On the other hand, identifying whether mitigation measures fulfil their expected objectives is also a key goal that may require a specific monitoring design focused on results achieved by a specific measure, or by a set of them. Evaluation based on key performance indicators is also recommended.

In practice, the main goals for evaluation are usually:

  • To identify and measure what effects are caused by the infrastructure on biodiversity.
  • To evaluate whether the mitigation actions applied provide long term mitigation or compensation for the species and habitats concerned.
  • To detect failures in mitigation measures installation, construction or maintenance which reduce its effectiveness (see Chapter 7 – Maintenance). If failures are detected corrective measures must be applied, and also evaluated to identify if they are being effective.

Appropriate monitoring and evaluation along the infrastructure’ life cycle is therefore crucial to achieve the following benefits:

  • Ensuring long term viability of wildlife populations and the preservation of healthy ecosystems and the services they provide.
  • Improving future design and maintenance of transport infrastructure, identifying actions with an optimal cost-effectiveness ratio and avoiding the repetition of mistakes and use of ineffective measures.
  • Ensuring a more efficient use of funds invested to mitigation measures.

Evaluating the impact of transport infrastructure on biodiversity

Evaluating the impact of transport infrastructure on nature using monitoring means defining clear goals and methods to be applied and collecting data on habitats and on the presence, abundance and diversity of species and populations before construction, during construction and, at least, in the first phases of operation (e.g., in some EU countries monitoring is mandatory over a period of 3 years but long term monitoring could be needed in some conditions).

Monitoring continues the biological survey process carried out during the planning phase (EIA, documentation for planning and building proceedings) and provides the results for further evaluation after a longer period of operation (3, 5, 10 years or longer). The description of changes in ecosystems, habitats and distribution and density of species during the design, construction, and operation provides information about the effects of transport infrastructure on wildlife. It is necessary to consider all relevant groups of species as well as habitats when proposing a monitoring plan.

Evaluating the impact of transport infrastructure on nature is a complex task which often requires using metrics on biodiversity state, but also other considerations such as meteorological data or information about the socio-economic transport infrastructure surrounding which may affect biodiversity independently or in interaction with other transport infrastructures (cumulative effects). If relevant, the way to collect existing data from external monitoring programmes such as meteorological surveys must also be considered or complemented if it is not sufficient or missing during the monitoring program duration (see Chapter 4 – Integration of infrastructure into the landscape for some examples).

Evaluating the effectiveness of mitigation measures

Measures to ensure the permeability of transport infrastructure for fauna and to reduce wildlife mortality (wildlife passages combined with fencing) are considered by many countries in recent decades as standard for most transport infrastructure projects. However, verification of whether the measures fulfil their purpose is often missing, poorly undertaken, or carried out with inadequate methods which lead to non conclusive results. These gaps in information are caused mostly by not clearly setting goals for the implementation of mitigation measures, which results in no possibilities to undertake appropriate assessment of their success. Authorities responsible for infrastructure design and construction usually perceive the implementation of mitigation measures as a formal obligation and do not prioritise monitoring their effectiveness. Consequently, failures in measures implemented go undetected and measures which are not fulfilling their purpose are often applied elsewhere. A key objective of evaluating effectiveness is to provide feedback to avoid errors and malfunctions.

Examples of goals for monitoring the effectiveness of implemented measures could be to evaluate:

  • Use of wildlife passages by target species.
  • Effects of wildlife passages on population size (which requires additional information to the example above)
  • Reduction of number of wildlife vehicle collisions after the installation of fences or use of artificial deterrents
  • Reduction of bird mortality from the application of measures to prevent collisions with powerlines.

Monitoring and evaluating the effectiveness of mitigation measures must be based on the identification of an initial state or biodiversity baseline which provides sufficiently precise information and is adapted to the context that will exist after the installation of the measure being evaluated. Measuring the effectiveness of fauna passages, for example, is often only focused on providing list of the species that use the passage and daily or monthly numbers using it. In this case, there will be little data to assess whether the number of individuals using the structure can guarantee a long-term conservation of a target species’ population. If the effectiveness of a wildlife passage at population level is to be measured in terms of gene flow, then the genetics of the populations on either side of the crossing must be assessed before the transport infrastructure is built, and after its construction for a period of time appropriate to the longevity of the species concerned.


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