Comment by MrJohz

As I understand it, the issue currently is that there's not really a framework for justifying or balancing those costs. Right now, the bat conservation people point out that the route will potentially eradicate a particular subspecies of bat. That gets sent up to the planning team, who now attempt to figure out a solution that prevents that from happening, and figures out how much that will cost. But what you probably want in between those points is someone to decide how much is too much to spend on the bats.

We do this for other stuff - for example, the NHS in the UK has a system called QALYs (Quality Adjusted Life Years) which represent how much a particular treatment will extend someone's life, adjusted by the quality of that life. You can then calculate a cost per QALY for a new treatment, and make a decision about what costs are worthwhile for the NHS to pay for, and what aren't.

Something like that that could apply to planning permission decisions would be very useful for national infrastructure projects.