Site Protection Measures under the Article 6 of the Habitats Directive
Assessment of plans and projects and compensatory measures
Article 6 (3) is an expression of the precautionary principle. An assessment is necessary where there are doubts as to the existence of significant effects. This could be the case, for example, where plans or projects may not be restrictively defined 
or where the preliminary consent already requires an assessment, such as land plan use. The assessment itself is a core mechanism of site protection and therefore the best scientific knowledge in the field must be used.
Generally, the assessment must precede the project’s approval and it has to be conform with conservation objectives. Its aim is to provide complete, precise and definitive findings and conclusions capable of removing all reasonable scientific doubts as to the work proposed.
The provisions of Article 6 (3) are not restricted to plans and projects which exclusively occur in or cover a protected site; they also target developments situated outside the site but likely to have a significant effect on it.
Article 6 (4) applies in cases of negative assessment, i.e. no consent under Article 6 (3) due to adverse effects or uncertainty.
The provisions of Article 6 (4) apply when the results of the preliminary assessment under Article 6 (3) are negative or uncertain. The sequential order of its steps has to be followed.
In exceptional circumstances, a plan or project may still be allowed to go ahead, provided that there are no alternative solutions and that the plan or project is considered to be of overriding public interest, such as health or public safety.
An overriding public interest only exists where it is of such importance that it can be weighed up against the conservation objective. Irrigation and the supply of drinking water can meet this importance; the construction of a management centre, however, does not.
European Commission: it is reasonable to consider that the ‘imperative reasons of overriding public interest, including those of a social and economic nature’ refer to situations where plans or projects envisaged prove to be indispensable:
- within the framework of actions or policies aiming to protect fundamental values for citizens’ lives (health, safety, environment);
- within the framework of fundamental policies for the state and society;
- within the framework of carrying out activities of an economic or social nature, fulfilling specific obligations of public service.