To be honest this is the worst possible time to view it as it is covered in growth.
The left side has been altered by flytipping but the right side curves back into itself so would be no good as a buttress for the road.
I recently found this
"Topographical sketches of North Wiltshire by John Britton, 1826.
p306
This shows Silbury hill was ancienter than the Roman road. The makers of the same Roman road cut through another barrow, of smaller dimensions, east of Silbury hill. "
If you get the chance to visit in Jan/feb then it looks a lot better.