The Aarhus Convention (in full here in English, in full here in many other languages) aims in its 22 Articles
The Convention covers explicitly "Construction of lines for long-distance railway traffic".
Unfortunately for badgers, not only has The Convention nothing to say about the management of wildlife, it contains an exclusion for short-term research and development under which current badger culling would probably fall.
In summary, we have a UN Convention, to which the UK is fully signed-up, that guarantees "rights of access to information, public participation in decision-making, and access to justice in environmental matters".
In my view that means plentiful, accessible and factually accurate data and interpretation backed-up by scientific research, together with procedures to ensure public participation. This goes further than the recent call for public disclosure on shale gas developments that was made to the Prime Minister and its follow-up.