Sorry Nigel, no more info on that one only a terse note at the visitor tent.
The strange "ruts" on the Avenue have sometimes been altered by some means. Should know a lot more when the new trench to the south of Atkinson's is excavated.
BTW I think this vast fence to keep the plebs out http://tinyurl.com/6z8gkq
is just a touch speculative, we will see.
Jim.