First, any concept of reasonable noise should be discarded. Second, as my colleagues as well as the people from the West have said, we would prefer the term “as little noise as possible”.
We took a look at what was being done in Europe, where rail transportation is light years ahead of ours. In England, particularly, noise is regulated according to decibel levels. Unfortunately, I don't have these documents with me, but I would suggest that you ask your researchers to take a look at what is being done in Europe, where a lot of good things are happening.