I was wondering if it is possible for you to tell whether these are new visitors or not.
Not easy ... and it probably depends on what you mean by "new". I would guess that the extra traffic's going to be a mixture of
* brand new guests who have never been to the site before
* guests who come only rarely (and if someone last visited in 2010, how "new" is (s)he this time)
* members who only come occasionally, and perhaps often visit as guests anyway
* frequently visiting members
Very hard to look way, way back for people who have been before - they may be using a different device on a different connection ... and even if they're cookie'd somewhere, cookies get deleted and timed out and we don't do them very long term anyway.
Is the increased traffic those of us who read here already checking that much more for updates and/or is there new traffic from people looking for the cause of the trouble and picking up the relevant threads in searches?
I would suspect that there is not a lot from new searches ... we're not indexed (to my knowledge) as a "news" site so that content gets offered within a few minutes - rather it takes time for it to make the indexes. Further more, we really don't have a sales and marketing / promotional pitch for what we've got here. There are questions that follow from that thought like "what is the forum for" and "how does the forum interact / relate to our train operator"; it has certainly changed over the years ...