Tony
There is a Drovers Route from South Wales that runs through Wessex and on to London. If the stones were moved by Human effect from Wales to Salisbury Plain (And that is a big if) I wonder if it was the Route taken. I have no idea if it would be at all practical for stone transport only that it is the route that cattle took...
How the stones would have gotten to this 'Main' Route I have again, no idea..
As far as I know the Stones came from some sites that were 15 kilometers apart. and given that there were 15 or more sites (I have read 20) that is a lot of ground to cover (Pun intended) What type of ground it was is probably unknown at this moment in time or how practical it would have been to move stones across it..
We do need a map..
Tony