https://theurbanprehistorian.wordpress.com/2015/04/20/drive-thru-henge/
A little railway line that appears to have serviced a prisoner of war camp at the end of the valley. This was in use in the First World War and there German prisoners were engaged in building the dam that holds back Camps Reservoir that now lies at the end of the little road which bisects the henge. This is one of only 39 such camps in Scotland associated with the Great War, and like most such camps, almost nothing is known about it and barely any traces survive (it has NMRS number NS92SE 66).
Ironic in a way that the henge was originally bisected by a railway as a hundred years ago there would have been few cars around. He mentions the obvious example of Avebury which seems to have had road going through it via its north and south entrances for centuries with a focal point being the water source/well in the middle - where the Red Lion now stands.